National Instruments Computer Accessories NI cDAQ 9172 User Manual

USER GUIDE AND SPECIFICATIONS  
NI cDAQ-9172  
This user guide describes how to use the National Instruments cDAQ-9172  
chassis and lists specifications. For an interactive demonstration of how to  
install the NI cDAQ-9172, go to ni.com/info and enter daqinstall.  
The NI cDAQ-9172 is an eight-slot USB chassis designed for use  
with C Series I/O modules. The NI cDAQ-9172 chassis is capable of  
measuring a broad range of analog and digital I/O and sensors using a  
Hi-Speed USB 2.0 interface. For module specifications, refer to the  
documentation included with your C Series I/O module(s) or go to  
ni.com/manuals.  
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NI cDAQ-9172  
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ON  
Ready  
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Active  
OFF  
11-30 VDC  
15 W  
4
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Power Switch  
5
6
7
Empty Module Slots  
Installed C Series I/O Modules  
Screw for Ground Connection  
Ready/Active LEDs  
Power Connector  
USB Connector  
Figure 1. NI cDAQ-9172  
Installing the NI cDAQ-9172  
Figure 2 shows the dimensions of the NI cDAQ-9172 chassis.  
19.0 mm  
(0.75 in.)  
165.1 mm  
(6.50 in.)  
NATIONAL  
INSTRUMENTS  
36.4 mm  
NI cDAQ-9172  
(1.43 in.)  
88.1 mm  
(3.50 in.)  
ON  
Ready  
Active  
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2
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OFF  
59.6 mm  
(2.35 in.)  
51.7 mm  
(2.04 in.)  
11-30 VDC  
15  
W
4.10 mm  
(0.16 in.)  
254.0 mm  
(10.00 in.)  
23.7 mm  
(0.94 in.)  
44.1 mm  
(1.74 in.)  
20.3 mm  
(0.80 in.)  
25.0 mm  
(0.98 in.)  
53.8 mm  
(2.12 in.)  
44.1 mm  
(1.74 in.)  
63.1 mm  
(2.49 in.)  
46.0 mm  
(1.81 in.)  
24.8 mm  
(0.98 in.)  
59.6 mm  
(2.35 in.)  
31.7 mm  
(1.25 in.)  
19.1 mm  
(0.75 in.)  
23.2 mm  
(0.91 in.)  
Figure 2. NI cDAQ-9172 with Dimensions in Millimeters (Inches)  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
Mounting the NI cDAQ-9172  
You can mount the NI cDAQ-9172 chassis using a desktop, a 35 mm  
DIN-Rail, or a panel mount accessory kit. For accessory ordering  
information, refer to ni.com.  
Caution Your installation must meet the following requirements:  
Allows 25.4 mm (1 in.) of clearance above and below the NI cDAQ-9172 chassis for  
air circulation.  
Allows 50.8 mm (2 in.) of clearance in front of modules for common connector  
cabling, such as the 10-terminal detachable screw terminal connector.  
NI 9901 Desktop Mounting Kit  
The NI 9901 Desktop Mounting Kit includes two metal feet you can install  
on the sides of the NI cDAQ-9172 chassis for desktop use. With this kit,  
you can tilt the NI cDAQ-9172 chassis for convenient access to the I/O  
module connectors. When you put on the two metal feet, the two existing  
screws on the power switch side of the chassis must be removed. After  
removing the screws, replace them with the two longer screws included in  
the NI 9901 Desktop Mounting Kit.  
Figure 3. NI 9901 Desktop Mounting Kit  
NI cDAQ-9172 User Guide and Specifications  
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ni.com  
Mounting the NI 9910 DIN-Rail Kit  
The NI 9910 DIN-Rail kit contains one clip for mounting the chassis on a  
standard 35 mm DIN-Rail. To mount the chassis on a DIN-Rail, fasten the  
DIN-Rail clip to the chassis using a number 2 Phillips screwdriver and  
two M4 × 16 screws. The screws are included in the DIN-Rail kit. Make  
sure the DIN-Rail kit is installed as illustrated in Figure 4, with the larger  
lip of the DIN-RAIL positioned up. When the DIN-Rail kit is properly  
installed, the NI cDAQ-9172 chassis is centered on the DIN-Rail.  
Caution Remove the I/O modules before removing the chassis from the DIN-Rail.  
Figure 4. DIN-Rail Dimensions and Installation on the NI cDAQ-9172  
Mounting the NI 9905 Panel Mount Kit  
To mount the chassis on a panel, align the chassis on the panel mount  
accessory. Attach the chassis to the panel mount kit using two M4 × 16  
screws (as pictured in the following diagram). National Instruments  
provides these screws with the panel mount kit. You must use these screws  
because they are the correct depth and thread for the panel. These slots in  
the panel mount kit can be used with M4, M5, No. 8, or No.10 panhead  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
screws. Figure 5 illustrates the panel dimensions and installation on the NI  
cDAQ-9172 chassis. Refer to the documentation included with the NI 9905  
shipping kit for more detailed dimensions.  
330.2 mm  
(13.00 in.)  
NATIONAL  
INSTRUMENTS  
NI cDAQ-9172  
ON  
88.1 mm  
(3.47 in.)  
Ready  
Active  
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4
5
6
7
8
OFF  
11-30 VDC  
15  
W
48.1 mm  
(1.90 in.)  
28.1 mm  
(1.11 in.)  
Figure 5. Panel Mount Dimensions and Installation on the NI cDAQ-9172  
NI cDAQ-9172 User Guide and Specifications  
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ni.com  
 
Setting Up the NI cDAQ-9172  
Complete the following steps to prepare the NI cDAQ-9172 chassis for use:  
1. Before connecting the hardware, install NI-DAQmx software,  
VI Logger, and the NI-DAQ Device Documentation Browser. Refer to  
the DAQ Getting Started Guide for more information about software  
installation.  
Note The NI-DAQmx software is included on the CD shipped with your kit and is  
available for download at ni.com/support. After you install it, the NI-DAQ Device  
Documentation Browser is available from Start»Programs»National Instruments»  
NI-DAQ»Browse Device Documentation. The DAQ Getting Started Guide is available  
after installation from Start»Programs»National Instruments»NI-DAQ»DAQ Getting  
Started Guide.  
2. If you are not using any mounting accessories, attach the provided  
rubber standoffs to the back of the NI cDAQ-9172 chassis.  
3. Make sure the NI cDAQ-9172 chassis power switch is turned off.  
4. Attach a ring lug to a 14 AWG (1.6 mm) wire. Connect the ring lug to  
the ground terminal on the side of the chassis using the ground screw.  
Attach the other end of the wire to the system safety ground.  
1
1
Attached to System Ground  
Figure 6. Ring Lug Attached to Ground Terminal  
Note Additionally, attach a wire with a ring lug to all other C Series I/O module cable  
shields. You must connect this wire to the ground terminal of the chassis using the ground  
screw.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
5. Remove the plastic cover from the connector in any empty module slot.  
6. Squeeze both C Series I/O module latches, insert the I/O module into  
the module slot, and press until both latches lock the module in place.  
7. Connect the NI cDAQ-9172 chassis with the supplied USB cable to  
any available USB port on your computer.  
8. Connect the power source to the NI cDAQ-9172 chassis. The  
NI cDAQ-9172 chassis requires an external power supply that meets  
the specifications in the Power Requirements section.  
Note The NI cDAQ-9172 chassis uses a DC input jack with a locking ring. Use only this  
connector with the NI cDAQ-9172 chassis. Refer to the Specifications section for more  
information about the connector.  
9. Secure the power supply and USB cables, as depicted in Figure 7,  
using the two tie wraps and adhesive tie wrap mounts included in the  
shipping kit. The tie wraps and adhesive mounts help secure the  
non-latching USB connection. They can also be used to route the  
cables to a desirable position.  
Q-9172  
A
NI cD  
Figure 7. cDAQ Chassis With Secured Cables  
10. Power on the NI cDAQ-9172 chassis.  
11. Double-click the Measurement & Automation icon, shown at left,  
on the desktop to open MAX.  
NI cDAQ-9172 User Guide and Specifications  
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ni.com  
 
12. Expand Devices and Interfaces, and then expand NI-DAQmx  
Devices.  
13. Check that your device appears under Devices and Interfaces. If your  
device does not appear, press <F5> to refresh the view in MAX. If your  
device is still not recognized, refer to ni.com/support/install for  
troubleshooting information.  
14. Right-click your device and select Self-Test.  
If you need help during the self-test, select Help»Help Topics»  
NI-DAQmx and click MAX Help for NI-DAQmx.  
When the self-test finishes, a message indicates successful verification  
or an error. If an error occurs, refer to ni.com/support/install  
for troubleshooting information.  
Note When in use, the NI cDAQ-9172 chassis may become warm to the touch. This is  
normal.  
Understanding LED Indications  
Active LED  
The Active LED indicates whether the NI cDAQ-9172 chassis is  
communicating over the USB bus.  
Table 1. Active LED  
LED  
Definition  
Amber  
Power is applied, but USB connection is not  
established  
Green  
Off  
USB traffic present  
No USB traffic present  
Ready LED  
The Ready LED is lit when the NI cDAQ-9172 chassis is ready for use. The  
color indicates whether the USB connection is Full-Speed or Hi-Speed.  
Table 2. Ready LED  
LED  
Definition  
Hi-Speed (480 Mbit/sec)  
Amber  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
Table 2. Ready LED (Continued)  
Definition  
LED  
Green  
Off  
Full-Speed (12 Mbit/sec)  
USB connection is not established  
Using the NI cDAQ-9172  
The cDAQ system consists of three parts: C Series I/O modules, the cDAQ  
module interface, and the USB-STC2. These components digitize signals,  
perform D/A conversions to generate analog output signals, measure and  
control digital I/O signals, and provide signal conditioning.  
C Series  
I/O Module  
cDAQ Module  
Interface  
USB-  
STC2  
USB  
2.0  
C Series  
I/O Module  
C Series  
I/O Module  
Figure 8. NI cDAQ-9172 Block Diagram  
C Series I/0 Modules  
National Instruments C Series I/O modules provide built-in signal  
conditioning and screw terminal, spring terminal, BNC, D-SUB, or  
RJ-50 connectors. A wide variety of I/O types are available, allowing  
you to customize the cDAQ system to meet your application needs.  
C Series I/O modules are hot-swappable and automatically detected by the  
NI cDAQ-9172 chassis. I/O channels are accessible using the NI-DAQmx  
driver software.  
Because the modules contain built-in signal conditioning for extended  
voltage ranges or industrial signal types, you can usually make your  
NI cDAQ-9172 User Guide and Specifications  
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ni.com  
 
wiring connections directly from the C Series I/O modules to your  
sensors/actuators. In most cases, the C Series I/O modules provide isolation  
from channel-to-earth ground.  
For more information about which C Series I/O modules are compatible  
with the NI cDAQ-9172 chassis, refer to the KnowledgeBase document,  
C Series Modules Supported in the NI cDAQ-9172. To access this  
KnowledgeBase, go to ni.com/info and enter the info code rdcdaq.  
Correlated vs. Static DIO Modules  
Digital I/O module capabilities are determined by the type of digital signals  
that the module is capable of measuring or generating. Static Digital I/O  
modules are designed for signals that change slowly and are accessed  
by software-timed reads and writes. Correlated Digital I/O modules are  
for signals that change rapidly and are updated by either software or  
hardware-timed reads and writes. Correlated Digital I/O modules can  
perform the following tasks:  
Used in any slot—software-timed reads and writes.  
Used in slots 1 though 4—Digital Waveform Generation and  
Acquisition (Correlated Input/Output)  
Used in slots 5 and 6—Counter/Timer  
Used in slots 5 and 6—Access PFI signals  
To determine the capability of digital I/O modules supported by the  
NI cDAQ-9172 chassis, refer to the KnowledgeBase document, C Series  
Modules Supported in the NI cDAQ-9172. To access this KnowledgeBase  
document, go to ni.com/info and enter the info code rdcdaq.  
cDAQ Module Interface  
The cDAQ Module Interface manages data transfers between the  
USB-STC2 and the C Series I/O modules. The interface also handles  
autodetection, signal routing, and synchronization.  
USB-STC2  
The USB-STC2 features independent High-Speed data streams; flexible  
AI and AO sample timing; triggering; PFI signals for multi-device  
synchronization; flexible counter/timers with hardware gating; digital  
waveform acquisition and generation; and static DIO.  
AI and AO Sample Timing  
The USB-STC2 contains advanced analog input and analog output timing  
engines. A wide range of timing and synchronization signals are available  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
through the PFI lines. Refer to the Analog Input Timing Signals and  
Analog Output Timing Signals sections for more information about the  
configuration of these signals.  
Triggering Modes  
The NI cDAQ-9172 supports different trigger modes, such as start trigger,  
reference trigger, and pause trigger with analog, digital, or software  
sources. Refer to the Analog Input Triggering and Analog Output  
Triggering sections for more information.  
Independent Data Streams  
The NI cDAQ-9172 supports four independent high-speed data streams;  
allowing for up to four simultaneous hardware timed tasks, such as analog  
input, analog output, buffered counter/timers, and correlated digital  
input/output.  
PFI Signals  
The PFI signals, available through correlated digital input and output  
modules installed in slots 5 and 6, provide access to advanced features such  
as triggering, synchronization, and counter/timers. Refer to the PFI section  
for more information.  
The PFI pins have a digital filter circuit at the inputs that is configurable on  
a per-line basis. The filters allow the rejection of noise caused by noisy  
environments, bounces on switches, and so on.  
Flexible Counter/Timers  
The NI cDAQ-9172 includes two general-purpose 32-bit counter/timers  
that can be used to count edges, measure pulse-widths, measure periods and  
frequencies, and perform position measurements (encoding). In addition,  
the counter/timers can generate pulses, pulse trains, and square waves with  
adjustable frequencies. You can access the counter inputs and outputs using  
correlated digital I/O modules in slots 5 and/or 6. Refer to the Counters  
section for more information.  
Analog Input  
To perform analog input measurements, insert a supported analog input  
C Series I/O module into any slot on the cDAQ chassis. The measurement  
specifications, such as number of channels, channel configuration, sample  
rate, and gain, are determined by the type of C Series I/O module used. For  
more information and wiring diagrams, refer to the documentation included  
with your C Series I/O modules.  
NI cDAQ-9172 User Guide and Specifications  
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ni.com  
The NI cDAQ-9172 has one AI timing engine, which means that only  
one analog input task may be running at a time on a chassis. However, the  
analog input task can include channels from multiple analog input modules.  
Analog Input Triggering  
A trigger is a signal that causes an action, such as starting or stopping the  
acquisition of data. When you configure a trigger, you must decide how  
you want to produce the trigger and the action you want the trigger to cause.  
The NI cDAQ-9172 chassis supports internal software triggering, external  
digital, and analog triggering.  
Three triggers are available: start trigger, reference trigger, and pause  
trigger. An analog or digital trigger can initiate these three trigger actions.  
Any C Series correlated digital input module can supply a digital trigger  
when installed in slots 5 or 6, and some C Series analog modules can supply  
an analog or digital trigger in any slot. The start, reference, and pause  
triggers can come from three separate modules if desired. To find your  
module triggering options, refer to the documentation included with your  
C Series I/O modules. For more information about using digital modules  
for triggering, refer to the Digital I/O section.  
AI Start Trigger Signal  
Use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement  
acquisition. A measurement acquisition consists of one or more samples. If  
you do not use triggers, begin a measurement with a software command.  
Once the acquisition begins, configure the acquisition to stop in one of the  
following ways:  
When a certain number of points is sampled (in finite mode)  
After a hardware reference trigger (in finite mode)  
With a software command (in continuous mode)  
An acquisition that uses a start trigger (but not a reference trigger) is  
sometimes referred to as a posttriggered acquisition. That is, samples are  
measured only after the trigger.  
When you are using an internal sample clock, you can specify a delay from  
the start trigger to the first sample.  
Using a Digital Source  
To use ai/StartTrigger with a digital source, specify a source and an edge.  
Use the following signals as the source:  
Any PFI terminal  
Counter n Internal Output  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
The source also can be one of several other internal signals on your  
NI cDAQ-9172 chassis. Refer to Device Routing in MAX in the  
NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more  
information.  
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
You also can specify whether the measurement acquisition begins on the  
rising edge or falling edge of ai/StartTrigger.  
Using an Analog Source  
Some C Series I/O modules can generate a trigger based on an analog  
signal. In NI-DAQmx, this is called the Analog Comparison Event.  
When you use an analog trigger source for ai/StartTrigger, the acquisition  
begins on the first rising or falling edge of the Analog Comparison Event  
signal, depending on the trigger properties.  
Routing AI Start Trigger to an Output Terminal  
You can route ai/StartTrigger to any output PFI terminal. The output is an  
active high pulse.  
AI Reference Trigger Signal  
Use a reference trigger (ai/ReferenceTrigger) signal to stop a measurement  
acquisition. To use a reference trigger, specify a buffer of finite size and  
a number of pretrigger samples (samples that occur before the reference  
trigger). The number of posttrigger samples (samples that occur after the  
reference trigger) desired is the buffer size minus the number of pretrigger  
samples.  
When the acquisition begins, the NI cDAQ-9172 chassis begins to fill the  
buffer. After the specified number of pretrigger samples are captured, the  
NI cDAQ-9172 begins to look for the reference trigger condition. If the  
reference trigger condition occurs before the NI cDAQ-9172 captures the  
specified number of pretrigger samples, the NI cDAQ-9172 ignores the  
condition.  
If the buffer becomes full, the NI cDAQ-9172 continuously discards the  
oldest samples in the buffer to make space for the next sample. This data  
can be accessed (with some limitations) before the NI cDAQ-9172 discards  
it. Refer to the KnowledgeBase document, Can a Pretriggered Acquisition  
NI cDAQ-9172 User Guide and Specifications  
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ni.com  
be Continuous?, for more information. To access this KnowledgeBase,  
go to ni.com/info and enter the info code rdcanq.  
When the reference trigger occurs, the NI cDAQ-9172 continues to write  
samples to the buffer until the buffer contains the number of posttrigger  
samples desired. Figure 9 shows the final buffer.  
Reference Trigger  
Pretrigger Samples  
Posttrigger Samples  
Complete Buffer  
Figure 9. Reference Trigger Final Buffer  
Using a Digital Source  
To use ai/ReferenceTrigger with a digital source, specify a source and an  
edge. Either PFI or one of several internal signals on the NI cDAQ-9172  
chassis can provide the source. Refer to Device Routing in MAX in the  
NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more  
information.  
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
You also can specify whether the measurement acquisition stops on the  
rising edge or falling edge of ai/ReferenceTrigger.  
Using an Analog Source  
Some C Series I/O modules can generate a trigger based on an analog  
signal. In NI-DAQmx, this is called the Analog Comparison Event.  
When you use an analog trigger source, the acquisition stops on the first  
rising or falling edge of the Analog Comparison Event signal, depending  
on the trigger properties.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
Routing AI Reference Trigger Signal to an Output Terminal  
You can route ai/ReferenceTrigger to any output PFI terminal.  
AI Pause Trigger Signal  
The Pause Trigger signal can be generated from internal or external  
sources. Any time the signal deasserts, you can use the Pause Trigger signal  
to pause the acquisition.  
You can use the AI Pause Trigger (ai/PauseTrigger) signal to pause and  
resume a measurement acquisition. The internal sample clock pauses while  
the external trigger signal is active and resumes when the signal is inactive.  
You can program the active level of the pause trigger to be high or low.  
Using a Digital Source  
To use ai/PauseTrigger, specify a source and a polarity. The source  
can be either from PFI or one of several other internal signals on  
your NI cDAQ-9172 chassis. Refer to Device Routing in MAX in the  
NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more  
information.  
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
Using an Analog Source  
Some C Series I/O modules can generate a trigger based on an analog  
signal. In NI-DAQmx, this is called the Analog Comparison Event.  
When you use an analog trigger source, the internal sample clock pauses  
when the Analog Comparison Event signal is low and resumes when the  
signal goes high (or vice versa).  
Note Pause triggers are only sensitive to the level of the source, not the edge.  
Analog Input Timing Signals  
AI Sample Clock  
A sample consists of one reading from each channel in the AI task.  
ai/SampleClock signals the start of a sample of all analog input channels  
in the task. ai/SampleClock can be generated from external or internal  
sources.  
NI cDAQ-9172 User Guide and Specifications  
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PFI  
Analog Comparison Event  
Ctr n Internal Output  
ai/SampleClock  
Sigma-Delta Module Internal Output  
PFI  
ai/SampleClock  
Timebase  
Analog Comparison  
Event  
Programmable  
Clock  
Divider  
20 MHz Timebase  
100 kHz Timebase  
Figure 10. Sample Clock Timing Options  
Routing AI Sample Clock to an Output Terminal  
You can route ai/SampleClock to any output PFI terminal.  
AI Sample Clock Timebase  
The AI Sample Clock Timebase (ai/SampleClockTimebase) signal is  
divided down to provide a source for ai/SampleClock. ai/SampleClock  
Timebase can be generated from external or internal sources.  
ai/SampleClockTimebase is not available as an output from the chassis.  
Convert Behavior For Analog Input Modules  
Scanned  
Scanned C Series analog input modules contain a single A/D converter and  
a multiplexer to select between multiple input channels. When the cDAQ  
Module Interface receives a Sample Clock pulse, it begins generating a  
Convert Clock for each scanned module in the current task. Each Convert  
Clock signals the acquisition of a single channel from that module. The  
Convert Clock rate depends on the module being used, the number of  
channels used on that module, and the system Sample Clock rate.  
The driver chooses the fastest conversion rate possible based on the speed  
of the A/D converter for each module and adds 10 µs of padding between  
each channel to allow for adequate settling time. This scheme enables the  
channels to approximate simultaneous sampling. If the AI Sample Clock  
rate is too fast to allow for 10 µs of padding, NI-DAQmx selects a  
conversion rate that spaces the AI Convert Clock pulses evenly throughout  
the sample. NI-DAQmx uses the same amount of padding for all the  
modules in the task. To explicitly specify the conversion rate, use the  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
ActiveDevs and AI Convert Clock Rate properties using the DAQmx  
Timing property node or functions.  
Simultaneous Sample-and-Hold  
Simultaneous sample-and-hold (SSH) C Series analog input modules  
contain multiple A/D converters or circuitry that allows all the input  
channels to be sampled at the same time. These modules sample their  
inputs on every Sample Clock pulse.  
Sigma-Delta  
Sigma-delta C Series analog input modules function much like SSH  
modules, but use A/D converters that require a high-frequency oversample  
clock to produce accurate, synchronized data. Sigma-delta modules in  
the cDAQ chassis automatically share a single oversample clock to  
synchronize data from all sigma-delta modules.  
This clock is used as the AI Sample Clock Timebase. While most modules  
supply a common oversample clock frequency (12.8 MHz), some modules,  
like the NI 9234, supply a different frequency. When sigma-delta modules  
with different oversample clock frequencies are used in an analog  
input task, the AI Sample Clock Timebase can use any of the available  
frequencies; by default, the fastest available is used. The sampling  
rate of all modules in the system is an integer divisor of the frequency  
of the AI Sample Clock Timebase.  
When one or more sigma-delta modules are in an analog input task, the  
sigma-delta modules also provide the signal used as the AI Sample Clock.  
This signal is used to cause A/D conversion for other modules in the  
system, just as the AI Sample Clock does when a sigma-delta module is not  
being used.  
When sigma-delta modules are in an AI task, the chassis automatically  
issues a synchronization pulse to each sigma-delta modules that resets their  
ADCs at the same time. Both the synchronization pulse and the oversample  
clock can be routed from or to any PFI line to allow synchronization  
between multiple chassis. Because of the filtering used in sigma-delta A/D  
converters, these modules usually exhibit a fixed input delay relative to  
non-sigma-delta modules in the system. This input delay is specified in the  
C Series I/O module documentation.  
Slow Sample Rate Modules  
Some C Series analog input modules are specifically designed for  
measuring signals that vary slowly, such as temperature. Because of their  
slow rate, it is not appropriate for these modules to constrain the AI Sample  
Clock to operate at or slower than their maximum rate. When using such a  
NI cDAQ-9172 User Guide and Specifications  
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module in the cDAQ chassis, the maximum Sample Clock rate can run  
faster than the maximum rate for the module. When operating at a rate  
faster than these slow rate modules can support, the slow rate module  
returns the same point repeatedly, until a new conversion completes. The  
first point is acquired when the task is committed. The second point is  
acquired after the start trigger.  
ai/StartTrigger  
1st A/D Conversion  
2nd A/D Conversion  
3rd A/D Conversion  
Data from  
A/D Conversion  
(Slow Module)  
A
B
C
C
ai/SampleClock  
Data Returned  
A
A
A
B
B
B
to AI Task  
Figure 11. Sample Clock Timing Example  
For example, if running an AI task at 1 kHz using a module with a  
maximum rate of 10 Hz, the slow module returns 100 samples of the first  
point, followed by 100 samples of the second point, etc. Other modules in  
the task will return 1,000 new data points per second, which is normal.  
When performing a single-point acquisition, no points are repeated.  
Refer to the KnowledgeBase document, C Series Modules Supported in the  
NI cDAQ-9172, for more information. To access this KnowledgeBase,  
go to ni.com/info and enter the info code rdcdaq.  
Getting Started with AI Applications in Software  
You can use the NI cDAQ-9172 chassis in the following analog input  
applications:  
Single-Point  
Finite  
Continuous  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
For more information about programming analog input applications and  
triggers in software, Refer to the NI-DAQmx Help or the LabVIEW Help in  
version 8.0 or later for more information.  
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
Analog Output  
To generate analog output, insert an analog output C Series I/O module in  
any slot on the NI cDAQ-9172 chassis. The generation specifications, such  
as the number of channels, channel configuration, update rate, and output  
range, are determined by the type of C Series I/O module used. For more  
information, refer to the documentation included with your C Series I/O  
modules.  
You can run one hardware-timed (waveform) analog output task at a time  
on the NI cDAQ-9172 chassis, with up to 16 waveform channels. At the  
same time, you can also run one or more software-timed (single-point or  
immediate) tasks.  
For each analog output module, you can either:  
Assign all of the channels on the module to the hardware-timed task.  
Assign all of the channels on the module to one or more  
software-timed tasks.  
On a single AO module, you cannot assign some channels to a  
hardware-timed task and other channels (on the same module) to  
a software-timed task.  
Analog Output Data Generation Methods  
When performing an analog output operation, you either can perform  
software-timed or hardware-timed generations. Hardware-timed  
generations must be buffered.  
Software-Timed Generations  
With a software-timed generation, software controls the rate at which data  
is generated. Software sends a separate command to the hardware to initiate  
each DAC conversion. In NI-DAQmx, software-timed generations are  
referred to as on-demand timing. Software-timed generations are also  
NI cDAQ-9172 User Guide and Specifications  
20  
ni.com  
referred to as immediate or static operations. They are typically used for  
writing out a single value, such as a constant DC voltage.  
The following considerations apply to software-timed generations:  
If any AO channel on a module is used in a hardware-timed  
(waveform) task, no channels on that module can be used in a  
software-timed task.  
You can configure software-timed generation to simultaneously  
update.  
Only one simultaneous update task can run at a time.  
Simultaneous update is not restricted to 16 channels.  
A hardware-timed AO task and a simultaneous update AO task cannot  
run at the same time.  
Hardware-Timed Generations  
With a hardware-timed generation, a digital hardware signal controls the  
rate of the generation. This signal can be generated internally on the chassis  
or provided externally.  
Hardware-timed generations have several advantages over software-timed  
acquisitions:  
The time between samples can be much shorter.  
The timing between samples is deterministic.  
Hardware-timed acquisitions can use hardware triggering.  
Hardware-timed AO operations on the NI cDAQ-9172 chassis must be  
buffered.  
Buffered Analog Output  
A buffer is a temporary storage in computer memory for generated  
samples. In a buffered generation, data is moved from a host buffer to the  
NI cDAQ-9172 onboard FIFO before it is written to the C Series I/O  
modules.  
One property of buffered I/O operations is sample mode. The sample mode  
can be either finite or continuous.  
Finite sample mode generation refers to the generation of a specific,  
predetermined number of data samples. Once the specified number of  
samples is written out, the generation stops.  
Continuous generation refers to the generation of an unspecified number of  
samples. Instead of generating a set number of data samples and stopping,  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
a continuous generation continues until you stop the operation. There are  
three different continuous generation modes that control how the data  
is written. These modes are regeneration, onboard regeneration, and  
non-regeneration.  
In regeneration mode, you define a buffer in host memory. The data from  
the buffer is continually downloaded to the FIFO to be written out. New  
data can be written to the host buffer at any time without disrupting the  
output.  
With onboard regeneration, the entire buffer is downloaded to the FIFO and  
regenerated from there. After the data is downloaded, new data cannot be  
written to the FIFO. To use onboard regeneration, the entire buffer must fit  
within the FIFO size. The advantage of using onboard regeneration is that  
it does not require communication with the main host memory once the  
operation is started, which prevents problems that may occur due to  
excessive bus traffic or operating system latency.  
With non-regeneration, old data is not repeated. New data must continually  
be written to the buffer. If the program does not write new data to the buffer  
at a fast enough rate to keep up with the generation, the buffer underflows  
and causes an error.  
Analog Output Triggering  
Analog output supports two different triggering actions:  
Start trigger  
Pause trigger  
An analog or digital trigger can initiate these actions. Any C Series  
correlated digital module in slots 5 and/or 6 can supply a digital trigger, and  
some C Series analog modules can supply an analog trigger. For more  
information refer to the AO Start Trigger Signal section of this document  
or to the documentation included with your C Series I/O module(s).  
Analog Output Timing Signals  
The NI cDAQ-9172 chassis features the following AO (waveform  
generation) timing signals:  
AO Sample Clock  
AO Start Trigger  
AO Pause Trigger  
NI cDAQ-9172 User Guide and Specifications  
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AO Sample Clock  
The AO sample clock signals when all the analog output channels in the  
task update. ao/SampleClock can be generated from external or internal  
sources.  
PFI  
Analog Comparison Event  
ao/SampleClock  
Ctr n Internal Output  
PFI  
ao/SampleClock  
Analog Comparison  
Event  
Timebase  
Programmable  
Clock  
Divider  
20 MHz Timebase  
100 kHz Timebase  
Figure 12. Analog Output Timing Options  
Routing AO Sample Clock to an Output Terminal  
You can route ao/SampleClock to any output PFI terminal.  
AO Sample Clock Timebase  
The AO Sample Clock Timebase (ao/SampleClockTimebase)  
signal is divided down to provide a source for ao/SampleClock.  
ao/SampleClockTimebase can be generated from external or internal  
sources, and is not available as an output from the chassis.  
AO Start Trigger Signal  
Use the AO Start Trigger (ao/StartTrigger) signal to initiate a waveform  
generation. If you do not use triggers, you can begin a generation  
with a software command. If you are using an internal sample clock,  
you can specify a delay from the start trigger to the first sample. For  
more information, refer to the NI-DAQmx Help. The NI-DAQmx Help is  
available after installation from Start»Programs»National Instruments»  
NI-DAQ»NI-DAQmx Help.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
Using a Digital Source  
To use ao/StartTrigger, specify a source and a rising or falling edge. The  
source can be one of the following signals:  
A software pulse  
Any PFI terminal  
ai/ReferenceTrigger  
ai/StartTrigger  
The source also can be one of several internal signals on the NI cDAQ-9172  
chassis. Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW Help in version 8.0 or later for more information.  
The NI-DAQmx Help is available after installation from Start»  
Programs»National Instruments»NI-DAQ»NI-DAQmx Help. To  
view the LabVIEW Help, in version 8.0 or later, select Help»Search the  
LabVIEW Help in LabVIEW. Alternately, to download the LabVIEW  
Help, go to ni.com/manuals.  
You also can specify whether the waveform generation begins on the rising  
edge or falling edge of ao/StartTrigger.  
Using an Analog Source  
Some C Series I/O modules can generate a trigger based on an analog  
signal. In NI-DAQmx, this is called the Analog Comparison Event,  
depending on the trigger properties.  
When you use an analog trigger source, the waveform generation begins on  
the first rising or falling edge of the Analog Comparison Event signal,  
depending on the trigger properties. The analog trigger circuit must be  
configured by a simultaneously running analog input task.  
Routing AO Start Trigger Signal to an Output Terminal  
You can route ao/StartTrigger to any output PFI terminal. The output is an  
active high pulse.  
AO Pause Trigger Signal  
Use the AO Pause trigger signal (ao/PauseTrigger) to mask off samples in  
a DAQ sequence. When ao/PauseTrigger is active, no samples occur, but  
ao/PauseTrigger does not stop a sample that is in progress. The pause does  
not take effect until the beginning of the next sample.  
NI cDAQ-9172 User Guide and Specifications  
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When you generate analog output signals, the generation pauses as soon as  
the pause trigger is asserted. If the source of the sample clock is the onboard  
clock, the generation resumes as soon as the pause trigger is deasserted, as  
shown in Figure 13.  
Pause Trigger  
Sample Clock  
Figure 13. ao/PauseTrigger with the Onboard Clock Source  
If you are using any signal other than the onboard clock as the source of  
the sample clock, the generation resumes as soon as the pause trigger is  
deasserted and another edge of the sample clock is received, as shown in  
Figure 14.  
Pause Trigger  
Sample Clock  
Figure 14. ao/PauseTrigger with Other Signal Source  
Using a Digital Source  
To use ao/PauseTrigger, specify a source and a polarity. The source can be  
a PFI signal or one of several other internal signals on the NI cDAQ-9172  
chassis.  
You also can specify whether the samples are paused when ao/PauseTrigger  
is at a logic high or low level. Refer to Device Routing in MAX in the  
NI-DAQmx Help or the LabVIEW Help in version 8.0 or later for more  
information.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
   
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
Using an Analog Source  
Some C Series I/O modules can generate a trigger based on an analog  
signal. In NI-DAQmx, this is called the Analog Comparison Event,  
depending on the trigger properties.  
When you use an analog trigger source, the samples are paused when the  
Analog Comparison Event signal is at a high or low level, depending on  
the trigger properties. The analog trigger circuit must be configured by  
a simultaneously running analog input task.  
Minimizing Glitches on the Output Signal  
When you use a DAC to generate a waveform, you may observe glitches  
on the output signal. These glitches are normal; when a DAC switches from  
one voltage to another, it produces glitches due to released charges. The  
largest glitches occur when the most significant bit of the DAC code  
changes. You can build a lowpass deglitching filter to remove some of  
these glitches, depending on the frequency and nature of the output signal.  
Go to ni.com/support for more information about minimizing glitches.  
Getting Started with AO Applications in Software  
You can use the NI cDAQ-9172 chassis in the following analog output  
applications:  
Single-Point (On-Demand) Generation  
Finite Generation  
Continuous Generation  
Waveform Generation  
For more information about programming analog output applications and  
triggers in software, refer the LabVIEW Help, in version 8.0 or later, or to  
the NI-DAQmx Help.  
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
NI cDAQ-9172 User Guide and Specifications  
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Digital I/O  
To use digital I/O, insert a digital C Series I/O module into any slot on  
the NI cDAQ-9172 chassis. The I/O specifications, such as number of lines,  
logic levels, update rate, and line direction, are determined by the type  
of C Series I/O module used. For more information, refer to the  
documentation included with your C Series I/O modules.  
Correlated vs. Static DIO Modules  
Digital I/O module capabilities are determined by the type of digital signals  
that the module is capable of measuring or generating. Static Digital I/O  
modules are designed for signals that change slowly and are accessed by  
software-timed reads and writes. Correlated Digital I/O modules are  
for signals that change rapidly and are updated by either software or  
hardware-timed reads and writes. Correlated Digital I/O modules can  
perform the following tasks:  
Used in any slot—software-timed reads and writes.  
Used in slots 1 though 4—Digital Waveform Generation and  
Acquisition (Correlated Input/Output)  
Used in slots 5 and 6—Counter/Timer  
Used in slots 5 and 6—Access PFI signals  
To determine the capability of digital I/O modules supported by the  
NI cDAQ-9172 chassis, refer to the KnowledgeBase document,  
C Series Modules Supported in the NI cDAQ-9172. To access this  
KnowledgeBase document, go to ni.com/info and enter the info code  
rdcdaq.  
Available features, such as trigger and counter/timer, are determined by the  
slot containing the digital C Series I/O module and the capabilities of the  
module.  
Table 3. Digital Module Slot Features  
Digital  
Waveform/Change  
Slots  
Static DIO  
Yes  
PFI1  
Counter/Timer1  
Detection1  
1
2
3
4
Yes  
Yes  
Yes  
Yes  
Yes  
Yes  
Yes  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
Table 3. Digital Module Slot Features (Continued)  
Digital  
Waveform/Change  
Detection1  
Slots  
Static DIO  
Yes  
PFI1  
Yes  
Yes  
Counter/Timer1  
5
6
7
8
Yes  
Yes  
Yes  
Yes  
Yes  
1 Requires the use of a correlated digital I/O module.  
Static DIO  
Each of the DIO lines can be used as a static DI or DO line. You can use  
static DIO lines to monitor or control digital signals on some C Series I/O  
modules. Each DIO line can be individually configured as a digital input  
(DI) or digital output (DO), depending on the C Series I/O module being  
used.  
All samples of static DI lines and updates of static DO lines are  
software-timed.  
Digital Waveform Acquisition (Correlated Input)  
You can acquire digital waveforms using correlated digital modules in  
slots 1 through 4. The DI waveform acquisition FIFO stores the digital  
samples. The NI cDAQ-9172 chassis samples the DIO lines on each rising  
or falling edge of the di/SampleClock signal.  
DI Sample Clock Signal  
Use the DI Sample Clock (di/SampleClock) signal to sample digital I/O on  
slots 1 through 4, using correlated digital modules, and store the result in  
the DI waveform acquisition FIFO. The NI cDAQ-9172 chassis does not  
have an independent DI Sample Clock circuit. Therefore, you must route  
an external signal or one of many internal signals from another subsystem  
to function as the DI Sample Clock. For example, you can correlate digital  
and analog samples in time by setting the AI Sample Clock or AO Sample  
Clock as the source of the DI Sample Clock. To sample a digital signal  
independent of an AI, AO, or DO operation, you can configure a counter  
to generate the desired DI Sample Clock or use an external signal as the  
source of the DI Sample Clock.  
If the NI cDAQ-9172 chassis receives a di/SampleClock signal when the  
FIFO is full, it reports an overflow error to the host software.  
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Using an Internal Source  
To use di/SampleClock with an internal source, specify the signal source  
and the polarity of the signal. Use the following signals as the source:  
AI Sample Clock  
AI Convert Clock  
AO Sample Clock  
Counter n Internal Output  
Frequency Output  
DI Change Detection Output  
Several other internal signals can be routed to di/SampleClock. Refer to  
Device Routing in MAX in the NI-DAQmx Help or the LabVIEW Help in  
version 8.0 or later for more information.  
The NI-DAQmx Help is available after installation from Start»Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help. To view the  
LabVIEW Help, in version 8.0 or later, select Help»Search the LabVIEW  
Help in LabVIEW. Alternately, to download the LabVIEW Help, go to  
ni.com/manuals.  
Using an External Source  
You can route the following signals as di/SampleClock:  
Any PFI terminal  
Analog Comparison Event (an analog trigger)  
You can sample data on the rising or falling edge of di/SampleClock.  
Routing DI Sample Clock to an Output Terminal  
You can route di/SampleClock to any output PFI terminal. The PFI  
circuitry inverts the polarity of di/SampleClock before driving the PFI  
terminal.  
Digital Waveform Generation (Correlated Output)  
With a hardware-timed generation, a digital hardware signal controls the  
rate of the generation. This signal can be generated internally on the chassis  
or provided externally.  
Hardware-timed generations have several advantages over software-timed  
acquisitions:  
The time between samples can be much shorter.  
The timing between samples can be deterministic.  
Hardware-timed operations must be buffered.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
Buffered Digital Waveform Generation  
A buffer is a temporary storage in computer memory for generated  
samples. In a buffered generation, data is moved from a host buffer to  
the NI cDAQ-9172 onboard FIFO before it is written to the C Series I/O  
modules. Buffered generations typically allow for much faster transfer  
rates than nonbuffered generations because data is moved in large blocks,  
rather than one point at a time. The DO sample clock causes all lines in the  
task to update at the same time.  
One property of buffered I/O operations is the sample mode. The sample  
mode can be either finite or continuous.  
Finite sample mode generation refers to the generation of a specific,  
predetermined number of data samples. Once the specified number of  
samples has been written out, the generation stops.  
Continuous generation refers to the generation of an unspecified number of  
samples. Instead of generating a set number of data samples and stopping,  
a continuous generation continues until you stop the operation. There are  
several different methods of continuous generation that control what data  
is written. These methods are regeneration, onboard regeneration, and  
non-regeneration modes.  
In regeneration mode, you define a buffer in host memory. The data from  
the buffer is continually downloaded to the FIFO to be written out. New  
data can be written to the host buffer at any time without disrupting the  
output.  
With onboard regeneration, the entire buffer is downloaded to the FIFO and  
regenerated from there. After the data is downloaded, new data cannot be  
written to the FIFO. To use onboard regeneration, the entire buffer must fit  
within the FIFO size. The advantage of using on board regeneration is that  
it does not require communication with the main host memory once the  
operation is started, thereby preventing any problems that may occur due to  
excessive bus traffic or operating system latency.  
With non-regeneration, old data is not repeated. New data must be  
continually written to the buffer. If the program does not write new data  
to the buffer at a fast enough rate to keep up with the generation, the buffer  
underflows and causes an error.  
NI cDAQ-9172 User Guide and Specifications  
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Change Detection Event  
The Change Detection Event is the signal generated when a change on the  
rising or falling edge lines is detected by the change detection task.  
Routing Change Detection Event to an Output  
Terminal  
You can route ChangeDetectionEvent to any output PFI terminal.  
Change Detection Acquisition  
You can configure lines on correlated digital modules in slots 1 through 4  
to detect rising or falling edges. When one or more of these lines sees the  
edge specified for that line, the NI cDAQ-9172 chassis samples all the lines  
in the task. The rising and falling edge lines do not necessarily have to be  
in the task.  
Change detection acquisitions can be buffered or nonbuffered.  
Nonbuffered Change Detection Acquisition  
In nonbuffered acquisitions, correlated digital input modules in any slot  
may be in the task, but the rising/falling edge detection lines must be in  
slots 1 through 4.  
Buffered Change Detection Acquisition  
A buffer is a temporary storage in computer memory for acquired samples.  
In a buffered acquisition, data is stored in the NI cDAQ-9172 onboard  
FIFO then transferred to a PC buffer. Buffered acquisitions typically allow  
for much faster transfer rates than nonbuffered acquisitions because data  
accumulates and is transferred in blocks, rather than one sample at a time.  
With buffered acquisitions, all modules in the task must be in slots 1  
through 4.  
Digital Input/Output Configuration for NI 9401  
When you change the configuration of lines on a NI 9401 digital I/O  
module between input and output, NI-DAQmx temporarily reserves all  
of the lines on the module for communication to send the module a line  
configuration command. If another task or route is actively using the  
module, to avoid interfering with the other task, NI-DAQmx generates an  
error instead of sending the line configuration command. During the line  
configuration command, the output lines are maintained without glitching.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
PFI  
You can configure channels of a correlated digital module in slots 5 and 6  
as Programmable Function Interface (PFI) terminals.  
You can configure each PFI individually as the following:  
Static digital input  
Static digital output  
Timing input signal for AI, AO, DI, DO, or counter/timer functions  
Timing output signal from AI, AO, DI, DO, or counter/timer functions  
Each PFI input also has a programmable digital filter circuit that is  
configurable on a per-line basis. The filters allow the rejection of noise  
caused by noisy environments, bounces on switches, and so on. Refer to the  
NI-DAQmx Help for more information. The NI-DAQmx Help is available  
after installation from Start»Programs»National Instruments»  
NI-DAQ»NI-DAQmx Help.  
Counters  
The NI cDAQ-9172 chassis has two general-purpose 32-bit counter/timers  
and one frequency generator, as shown in Figure 15. The general-purpose  
counter/timers can be used for many measurement and pulse generation  
applications.  
Some counter/timer signals may be routed to PFI signals. To access PFI  
signals, you must use a correlated digital C Series I/O module in slot 5 or 6.  
Note For more information about C Series signal connections for counters, refer to  
the NI-DAQmx Help. The NI-DAQmx Help is available after installation from Start»  
Programs»National Instruments»NI-DAQ»NI-DAQmx Help.  
NI cDAQ-9172 User Guide and Specifications  
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Input Selection Muxes  
Input Selection Muxes  
Input Selection Muxes  
Counter 0  
Counter 0 Source (Counter 0 Timebase)  
Counter 0 Gate  
Counter 0 Internal Output  
Counter 0 Aux  
Counter 0 HW Arm  
Counter 0 A  
Counter 0 TC  
Counter 0 B (Counter 0 Up_Down)  
Counter 0 Z  
Counter 1  
Counter 1 Source (Counter 1 Timebase)  
Counter 1 Gate  
Counter 1 Internal Output  
Counter 1 Aux  
Counter 1 HW Arm  
Counter 1 A  
Counter 1 TC  
Counter 1 B (Counter 1 Up_Down)  
Counter 1 Z  
Frequency Generator  
Frequency Output Timebase  
Freq Out  
Figure 15. NI cDAQ-9172 Counters  
Counters have seven input signals, although in most applications only a few  
inputs are used.  
For information about connecting the counter signals, refer to the Default  
Counter/Timer Routing section. The following sections describe various  
counter applications.  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
 
Counter Input Applications  
Counting Edges  
In edge counting applications, the counter counts edges on its Source after  
the counter is armed. You can configure the counter to count rising or  
falling edges on its Source input. You also can control the direction of  
counting (up or down).  
The counter values can be read on demand or with a sample clock.  
Single-Point (On-Demand) Edge Counting  
With single-point (on-demand) edge counting, the counter counts the  
number of edges on the Source input after the counter is armed. On-demand  
refers to the fact that software can read the counter contents at any time  
without disturbing the counting process. Figure 16 shows an example of  
single-point edge counting.  
Counter Armed  
SOURCE  
Counter Value  
0
1
2
3
4
5
Figure 16. Single-Point (On-Demand) Edge Counting  
You also can use a pause trigger to pause (or gate) the counter. When the  
pause trigger is active, the counter ignores edges on its Source input. When  
the pause trigger is inactive, the counter counts edges normally.  
NI cDAQ-9172 User Guide and Specifications  
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You can route the pause trigger to the Gate input of the counter. You can  
configure the counter to pause counting when the pause trigger is high or  
when it is low. Figure 17 shows an example of on-demand edge counting  
with a pause trigger.  
Counter Armed  
Pause Trigger  
(Pause When Low)  
SOURCE  
0
0
1
2
3
4
5
Counter Value  
Figure 17. Single-Point (On-Demand) Edge Counting with Pause Trigger  
Buffered (Sample Clock) Edge Counting  
With buffered edge counting (edge counting using a sample clock), the  
counter counts the number of edges on the Source input after the counter is  
armed. The value of the counter is sampled on each active edge of a sample  
clock. The NI cDAQ-9172 transfers the sampled values to host memory.  
The count values returned are the cumulative counts since the counter  
armed event. That is, the sample clock does not reset the counter.  
You can route the counter sample clock to the Gate input of the counter. You  
can configure the counter to sample on the rising or falling edge of the  
sample clock.  
Figure 18 shows an example of buffered edge counting. Notice that  
counting begins when the counter is armed, which occurs before the  
first active edge on Gate.  
Counter Armed  
Sample Clock  
(Sample on Rising Edge)  
SOURCE  
Counter Value  
Buffer  
0
1
2
3
4
3
5
6
7
3
6
Figure 18. Buffered (Sample Clock) Edge Counting  
© National Instruments Corporation  
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NI cDAQ-9172 User Guide and Specifications  
   
Controlling the Direction of Counting  
In edge counting applications, the counter can count up or down. You can  
configure the counter to do the following:  
Always count up  
Always count down  
Count up when the Counter n B input is high; count down when  
it is low  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
Pulse-Width Measurement  
In pulse-width measurements, the counter measures the width of a pulse on  
its Gate input signal. You can configure the counter to measure the width  
of high pulses or low pulses on the Gate signal.  
You can route an internal or external periodic clock signal (with a known  
period) to the Source input of the counter. The counter counts the number  
of rising (or falling) edges on the Source signal while the pulse on the Gate  
signal is active.  
You can calculate the pulse width by multiplying the period of the Source  
signal by the number of edges returned by the counter.  
A pulse-width measurement is accurate even if the counter is armed while  
a pulse train is in progress. If a counter is armed while the pulse is in the  
active state, it waits for the next transition to the active state to begin the  
measurement.  
Single Pulse-Width Measurement  
With single pulse-width measurement, the counter counts the number of  
edges on the Source input while the Gate input remains active. When the  
Gate input goes inactive, the counter stores the count in a hardware save  
register and ignores other edges on the Gate and Source inputs. The  
software then reads the stored count.  
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Figure 19 shows an example of a single pulse-width measurement.  
GATE  
SOURCE  
Counter Value  
0
1
2
HW Save Register  
2
Figure 19. Single Pulse-Width Measurement  
Buffered Pulse-Width Measurement  
Buffered pulse-width measurement is similar to single pulse-width  
measurement, but buffered pulse-width measurement takes measurements  
over multiple pulses.  
The counter counts the number of edges on the Source input while the Gate  
input remains active. On each trailing edge of the Gate signal, the counter  
stores the count in a hardware save register. The NI cDAQ-9172 transfers  
the stored values to host memory.  
Figure 20 shows an example of a buffered pulse-width measurement.  
GATE  
SOURCE  
0
1
2
3
1
2
Counter Value  
Buffer  
3
3
2
3
2
Figure 20. Buffered Pulse-Width Measurement  
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occur between each active edge of the Gate signal. This condition ensures that correct  
values are returned by the counter. If this condition is not met, consider using duplicate  
count prevention, described in the Duplicate Count Prevention section.  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
Period Measurement  
In period measurements, the counter measures a period on its Gate input  
signal after the counter is armed. You can configure the counter to measure  
the period between two rising edges or two falling edges of the Gate input  
signal.  
You can route an internal or external periodic clock signal (with a known  
period) to the Source input of the counter. The counter counts the number  
of rising (or falling) edges occurring on the Source input between the  
two active edges of the Gate signal.  
You can calculate the period of the Gate input by multiplying the period of  
the Source signal by the number of edges returned by the counter.  
Single Period Measurement  
With single period measurement, the counter counts the number of rising  
(or falling) edges on the Source input occurring between two active edges  
of the Gate input. On the second active edge of the Gate input, the counter  
stores the count in a hardware save register and ignores other edges on the  
Gate and Source inputs. The software then reads the stored count.  
Figure 21 shows an example of a single period measurement.  
GATE  
SOURCE  
Counter Value  
0
1
2
3
4
5
HW Save Register  
5
Figure 21. Single Period Measurement  
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Buffered Period Measurement  
Buffered period measurement is similar to single period measurement,  
but buffered period measurement measures multiple periods.  
The counter counts the number of rising (or falling) edges on the Source  
input between each pair of active edges on the Gate input. At the end of  
each period on the Gate signal, the counter stores the count in a hardware  
save register. The NI cDAQ-9172 transfers the stored values to host  
memory.  
The counter begins when it is armed. The arm usually occurs in the middle  
of a period of the Gate input. So the first value stored in the hardware save  
register does not reflect a full period of the Gate input. In most applications,  
this first point should be discarded.  
Figure 22 shows an example of a buffered period measurement.  
Counter Armed  
GATE  
SOURCE  
Counter Value  
1
2
1
2
3
1
2
3
1
2
3
3
2 (Discard)  
(Discard)  
2 (Discard)  
3
3
2
3
Buffer  
Figure 22. Buffered Period Measurement  
occur between each active edge of the Gate signal. This condition ensures that correct  
values are returned by the counter. If this condition is not met, consider using duplicate  
count prevention, described in the Duplicate Count Prevention section.  
For information about connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
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Semi-Period Measurement  
In semi-period measurements, the counter measures a semi-period on its  
Gate input signal after the counter is armed. A semi-period is the time  
between any two consecutive edges on the Gate input.  
You can route an internal or external periodic clock signal (with a  
known period) to the Source input of the counter. The counter counts  
the number of rising (or falling) edges occurring on the Source input  
between two edges of the Gate signal.  
You can calculate the semi-period of the Gate input by multiplying the  
period of the Source signal by the number of edges returned by the counter.  
Single Semi-Period Measurement  
Single semi-period measurement is equivalent to single pulse-width  
measurement.  
Buffered Semi-Period Measurement  
In buffered semi-period measurement, on each edge of the Gate signal, the  
counter stores the count in a hardware save register. The NI cDAQ-9172  
transfers the stored values to host memory.  
The counter begins counting when it is armed. The arm usually occurs  
between edges on the Gate input, which means that the first value stored in  
the hardware save register does not reflect a full semi-period of the Gate  
input. In most applications, this first point should be discarded.  
Figure 23 shows an example of a buffered semi-period measurement.  
Counter Armed  
GATE  
SOURCE  
Counter Value  
Buffer  
0
1
2
1
2
3
1
1
2
1
2
3
2
3
1
2
2
3
1
2
2
3
1
2
Figure 23. Buffered Semi-Period Measurement  
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occur between each active edge of the Gate signal. This condition ensures that correct  
values are returned by the counter. If this condition is not met, consider using duplicate  
count prevention, described in the Duplicate Count Prevention section.  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
Frequency Measurement  
You can use the counters to measure frequency in several different ways.  
You can choose one of the following methods depending on your  
application: Method 1, Method 1b, Method 2, and Method 3.  
Method 1—Measure Low Frequency With One Counter  
This method is good for low frequency signals. Use this method to measure  
one period of your signal using a known timebase. Figure 24 illustrates this  
method.  
Interval Measured  
F1  
F1  
Ft  
Gate  
1
2
3
N
Source  
Ft  
N
Single Period  
Measurement  
Period of F1 =  
Ft  
Ft  
N
Frequency of F1 =  
Figure 24. Frequency Measurement—Method 1  
You can route the signal to measure (F1) to the Gate of a counter. You can  
route a known timebase (Ft) to the Source of the counter. The known  
timebase can be 80MHzTimebase. For signals that might be slower than  
0.02 Hz, use a slower known timebase.  
You can configure the counter to measure one period of the gate signal. The  
frequency of F1 is the inverse of the period.  
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Method 1b—Measure Low Frequency With One Counter  
(Averaged)  
This method is good for low to medium frequency signals. Use this method  
to measure several periods of your signal using a known timebase.  
Figure 25 illustrates this method.  
Intervals Measured  
T1  
T2  
TK  
F1  
Ft  
Gate  
F1  
Ft  
12...N11......N2  
1......NK  
Source  
Buffered Period  
Measurement  
N1 + N2 + …NK  
1
×
Average Period of F1 =  
Frequency of F1 =  
K
Ft  
K × Ft  
N1 + N2 + …NK  
Figure 25. Frequency Measurement—Method 1b  
You can route the signal to measure (F1) to the Gate of a counter. You can  
route a known timebase (Ft) to the Source of the counter. The known  
timebase can be 80MHzTimebase. For signals that might be slower than  
0.02 Hz, use a slower known timebase.  
You can configure the counter to make K + 1 buffered period  
measurements. Recall that the first period measurement in the buffer  
should be discarded.  
Average the remaining K period measurements to determine the average  
period of F1. The frequency of F1 is the inverse of the average period.  
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Method 2—Measure High Frequency With Two Counters  
This method is good for high frequency signals. Use this method to  
measure one pulse of a known width using your signal and derive the  
frequency of your signal from the result. Figure 26 illustrates this method.  
Width of Pulse (T)  
Pulse  
Pulse  
F1  
Gate  
1
2
N
Source  
F1  
N
Pulse-Width  
Measurement  
Width of  
Pulse  
T =  
F1  
N
T
Frequency of F1 =  
Figure 26. Frequency Measurement—Method 2  
In this method, you route a pulse of known duration (T) to the Gate of a  
counter. You can generate the pulse using a second counter. You also can  
generate the pulse externally and connect it to a PFI terminal. You only  
need to use one counter if you generate the pulse externally.  
Route the signal to measure (F1) to the Source of the counter. Configure the  
counter for a single pulse-width measurement. Suppose you measure the  
width of pulse T to be N periods of F1. Then the frequency of F1 is N/T.  
Another option would be to measure the width of a known period instead  
of a known pulse.  
Method 3—Measure Large Range of Frequencies Using  
Two Counters  
By using two counters, you can accurately measure a signal that might  
be high or low frequency. This technique is called reciprocal frequency  
measurement. In this method, you generate a long pulse using the signal to  
measure. You then measure the long pulse with a known timebase. The  
NI cDAQ-9172 chassis can measure this long pulse more accurately than  
the faster input signal.  
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You can route the signal to measure to the Source input of Counter 0, as  
shown in Figure 27. Assume this signal to measure has frequency F1.  
Configure Counter 0 to generate a single pulse that is the width of N periods  
of the source input signal.  
Signal to  
Measure (F1)  
SOURCE  
COUNTER 0  
OUT  
Signal of Known  
Frequency (F2)  
SOURCE  
OUT  
COUNTER 1  
GATE  
2
0
1
3
N  
CTR_0_SOURCE  
(Signal to Measure)  
CTR_0_OUT  
(CTR_1_GATE)  
Interval to  
Measure  
CTR_1_SOURCE  
Figure 27. Frequency Measurement—Method 3  
Then route the Counter 0 Internal Output signal to the Gate input of  
Counter 1. You can route a signal of known frequency (F2) to the Counter 1  
Source input. F2 can be 80MHzTimebase. For signals that might be slower  
than 0.02 Hz, use a slower known timebase. Configure Counter 1 to  
perform a single pulse-width measurement. Suppose the result is that the  
pulse width is J periods of the F2 clock.  
From Counter 0, the length of the pulse is N/F1. From Counter 1, the length  
of the same pulse is J/F2. Therefore, the frequency of F1 is given by  
F1 = F2 * (N/J).  
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Choosing a Method for Measuring Frequency  
The best method to measure frequency depends on several factors  
including the expected frequency of the signal to measures, the desired  
accuracy, how many counters are available and how long the measurement  
can take.  
Method 1 uses only one counter. It is a good method for many  
applications. However, the accuracy of the measurement decreases  
as the frequency increases.  
Consider a frequency measurement on a 50 kHz signal using an  
80 MHz Timebase. This frequency corresponds to 1600 cycles of the  
80 MHz Timebase. Your measurement may return 1600 1 cycles  
depending on the phase of the signal with respect to the timebase. As  
your frequency becomes larger, this error of 1 cycle becomes more  
significant, as Table 4 illustrates.  
Table 4. Frequency Measurement Method 1  
Task  
Equation  
Example 1  
50 kHz  
Example 2  
5 MHz  
Actual Frequency to Measure  
Timebase Frequency  
F1  
Ft  
80 MHz  
1600  
80 MHz  
16  
Actual Number of Timebase  
Periods  
Ft/F1  
Worst Case Measured Number (Ft/F1) – 1  
of Timebase Periods  
1599  
15  
Measured Frequency  
Error  
Ft F1/(Ft – F1)  
50.031 kHz  
31 Hz  
5.33 MHz  
333 kHz  
6.67%  
[Ft F1/(Ft – F1)] – F1  
[Ft/(Ft – F1)] – 1  
Error %  
0.06%  
Method 1b (measuring K periods of F1) improves the accuracy  
of the measurement. A disadvantage of Method 1b is that K + 1  
measurements are required. These measurements take more time  
and consume some of the available USB bandwidth.  
Method 2 is accurate for high frequency signals. However, the  
accuracy decreases as the frequency of the signal to measure  
decreases. At very low frequencies, Method 2 may be too inaccurate  
for your application. Another disadvantage of Method 2 is that it  
requires two counters (if you cannot provide an external signal of  
known width). An advantage of Method 2 is that the measurement  
completes in a known amount of time.  
Method 3 measures high and low frequency signals accurately.  
However, it requires two counters.  
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Table 5 summarizes some of the differences in methods of measuring  
frequency.  
Table 5. Frequency Measurement Method Comparison  
Measures High  
Frequency  
Signals  
Measures Low  
Frequency  
Signals  
Number of  
Measurements  
Returned  
Number of  
Counters Used  
Method  
Accurately  
Accurately  
1
1b  
2
1
1
1
Many  
1
Poor  
Fair  
Good  
Good  
Poor  
1 or 2  
2
Good  
Good  
3
1
Good  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
Position Measurement  
You can use the counters to perform position measurements with  
quadrature encoders or two-pulse encoders. You can measure angular  
position with X1, X2, and X4 angular encoders. Linear position can be  
measured with two-pulse encoders. You can choose to do a single-point  
(on-demand) position measurement or a buffered (sample clock) position  
measurement. You must arm a counter to begin position measurements.  
Measurements Using Quadrature Encoders  
The counters can perform measurements of quadrature encoders that  
use X1, X2, or X4 encoding. A quadrature encoder can have up to  
three channels—channels A, B, and Z.  
X1 Encoding  
When channel A leads channel B in a quadrature cycle, the counter  
increments. When channel B leads channel A in a quadrature cycle, the  
counter decrements. The amount of increments and decrements per cycle  
depends on the type of encoding—X1, X2, or X4.  
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Figure 28 shows a quadrature cycle and the resulting increments and  
decrements for X1 encoding. When channel A leads channel B, the  
increment occurs on the rising edge of channel A. When channel B leads  
channel A, the decrement occurs on the falling edge of channel A.  
Ch A  
Ch B  
Counter Value  
6
7
7
6
5
5
Figure 28. X1 Encoding  
X2 Encoding  
The same behavior holds for X2 encoding except the counter increments or  
decrements on each edge of channel A, depending on which channel leads  
the other. Each cycle results in two increments or decrements, as shown in  
Figure 29.  
Ch A  
Ch B  
Counter Value  
5
6
7
8
9
9
8
7
6
5
Figure 29. X2 Encoding  
X4 Encoding  
The counter increments or decrements similarly on each edge of  
channels A and B for X4 encoding. Whether the counter increments or  
decrements depends on which channel leads the other. Each cycle results in  
four increments or decrements, as shown in Figure 30.  
Ch A  
Ch B  
Counter Value  
5
6
7
8
9
10 11 12 13 13 12 11 10  
9
8
7
6
5
Figure 30. X4 Encoding  
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Channel Z Behavior  
Some quadrature encoders have a third channel, channel Z, which is also  
referred to as the index channel. A high level on channel Z causes the  
counter to be reloaded with a specified value in a specified phase of the  
quadrature cycle. You can program this reload to occur in any one of the  
four phases in a quadrature cycle.  
Channel Z behavior—when it goes high and how long it stays  
high—differs with quadrature encoder designs. You must refer to the  
documentation for your quadrature encoder to obtain timing of channel Z  
with respect to channels A and B. You must then ensure that channel Z is  
high during at least a portion of the phase you specify for reload. For  
example, in Figure 31, channel Z is never high when channel A is high  
and channel B is low. Thus, the reload must occur in some other phase.  
In Figure 31, the reload phase is when both channel A and channel B are  
low. The reload occurs when this phase is true and channel Z is high.  
Incrementing and decrementing takes priority over reloading. Thus, when  
the channel B goes low to enter the reload phase, the increment occurs first.  
The reload occurs within one maximum timebase period after the reload  
phase becomes true. After the reload occurs, the counter continues counting  
as before. The figure illustrates channel Z reload with X4 decoding.  
Ch A  
Ch B  
Ch Z  
Max Timebase  
Counter Value  
5
6
7
8
9
0
1
2
3
4
A = 0  
B = 0  
Z = 1  
Figure 31. Channel Z Reload with X4 Decoding  
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Measurements Using Two Pulse Encoders  
The counter supports two pulse encoders that have two channels—channels  
A and B.  
The counter increments on each rising edge of channel A. The counter  
decrements on each rising edge of channel B, as shown in Figure 32.  
Ch A  
Ch B  
Counter Value  
2
3
4
5
4
3
4
Figure 32. Measurements Using Two Pulse Encoders  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
Two-Signal Edge-Separation Measurement  
Two-signal edge-separation measurement is similar to pulse-width  
measurement, except that there are two measurement signals—AUX and  
Gate. An active edge on the AUX input starts the counting and an active  
edge on the Gate input stops the counting. You must arm a counter to begin  
a two edge separation measurement.  
After the counter has been armed and an active edge occurs on the AUX  
input, the counter counts the number of rising (or falling) edges on the  
Source. The counter ignores additional edges on the AUX input.  
The counter stops counting upon receiving an active edge on the Gate input.  
The counter stores the count in a hardware save register.  
You can configure the rising or falling edge of the AUX input or the Gate  
input to be the active edge.  
Use this type of measurement to count events or measure the time that  
occurs between edges on two signals. This type of measurement is  
sometimes referred to as start/stop trigger measurement, second gate  
measurement, or A-to-B measurement.  
Single Two-Signal Edge-Separation Measurement  
With single two-signal edge-separation measurement, the counter counts  
the number of rising (or falling) edges on the Source input occurring  
between an active edge of the Gate signal and an active edge of the AUX  
signal. The counter then stores the count in a hardware save register and  
ignores other edges on its inputs. Software then reads the stored count.  
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Figure 33 shows an example of a single two-signal edge-separation  
measurement.  
Counter  
Armed  
Measured Interval  
AUX  
GATE  
SOURCE  
Counter Value  
0
0
0
0
1
2
3
4
5
6
7
8
8
8
HW Save Register  
8
Figure 33. Single Two-Signal Edge-Separation Measurement  
Buffered Two-Signal Edge-Separation Measurement  
Buffered and single two-signal edge-separation measurements are similar,  
but buffered measurement measures multiple intervals.  
The counter counts the number of rising (or falling) edges on the Source  
input occurring between an active edge of the Gate signal and an active  
edge of the AUX signal. The counter then stores the count in a hardware  
save register. On the next active edge of the Gate signal, the counter begins  
another measurement. The NI cDAQ-9172 transfers the stored values to  
host memory.  
Figure 34 shows an example of a buffered two-signal edge-separation  
measurement.  
AUX  
GATE  
SOURCE  
Counter Value  
1
2
3
1
2
3
1
2
3
3
3
3
3
3
3
Figure 34. Buffered Two-Signal Edge-Separation Measurement  
For information about connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
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Counter Output Applications  
Simple Pulse Generation  
The counter can output a single pulse. The pulse appears on the Counter n  
Internal Output signal of the counter.  
You can specify a delay from when the counter is armed to the beginning  
of the pulse. The delay is measured in terms of a number of active edges of  
the Source input.  
You can specify a pulse width. The pulse width is also measured in terms  
of a number of active edges of the Source input. You also can specify the  
active edge of the Source input (rising or falling).  
Figure 35 shows a generation of a pulse with a pulse delay of four and a  
pulse width of three (using the rising edge of Source).  
Counter Armed  
SOURCE  
OUT  
Figure 35. Single Pulse Generation  
Single Pulse Generation with Start Trigger  
The counter can output a single pulse in response to one pulse on a  
hardware Start Trigger signal. The pulse appears on the Counter n Internal  
Output signal of the counter.  
You can route the Start Trigger signal to the Gate input of the counter. You  
can specify a delay from the Start Trigger to the beginning of the pulse. You  
also can specify the pulse width. The delay and pulse width are measured  
in terms of a number of active edges of the Source input.  
After the Start Trigger signal pulses once, the counter ignores the Gate  
input.  
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Figure 36 shows a generation of a pulse with a pulse delay of four and a  
pulse width of three (using the rising edge of Source).  
GATE  
(Start Trigger)  
SOURCE  
OUT  
Figure 36. Single Pulse Generation with Start Trigger  
Retriggerable Single Pulse Generation  
The counter can output a single pulse in response to each pulse on a  
hardware Start Trigger signal. The pulses appear on the Counter n Internal  
Output signal of the counter.  
You can route the Start Trigger signal to the Gate input of the counter. You  
can specify a delay from the Start Trigger to the beginning of each pulse.  
You also can specify the pulse width. The delay and pulse width are  
measured in terms of a number of active edges of the Source input.  
The counter ignores the Gate input while a pulse generation is in progress.  
After the pulse generation is finished, the counter waits for another Start  
Trigger signal to begin another pulse generation.  
Figure 37 shows a generation of two pulses with a pulse delay of five and a  
pulse width of three (using the rising edge of Source).  
GATE  
(Start Trigger)  
SOURCE  
Figure 37. Retriggerable Single Pulse Generation  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
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Pulse Train Generation  
Continuous Pulse Train Generation  
This function generates a train of pulses with programmable frequency and  
duty cycle. The pulses appear on the Counter n Internal Output signal of the  
counter.  
You can specify a delay from when the counter is armed to the beginning  
of the pulse train. The delay is measured in terms of a number of active  
edges of the Source input.  
You specify the high and low pulse widths of the output signal. The pulse  
widths are also measured in terms of a number of active edges of the Source  
input. You also can specify the active edge of the Source input (rising or  
falling).  
The counter can begin the pulse train generation as soon as the counter is  
armed, or in response to a hardware Start Trigger. You can route the Start  
Trigger to the Gate input of the counter.  
You also can use the Gate input of the counter as a Pause Trigger (if it is not  
used as a Start Trigger). The counter pauses pulse generation when the  
Pause Trigger is active.  
Figure 38 shows a continuous pulse train generation (using the rising edge  
of Source).  
SOURCE  
OUT  
Counter Armed  
Figure 38. Continuous Pulse Train Generation  
Continuous pulse train generation is sometimes called frequency division.  
If the high and low pulse widths of the output signal are M and N periods,  
then the frequency of the Counter n Internal Output signal is equal to the  
frequency of the Source input divided by M + N.  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
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Frequency Generation  
You can generate a frequency by using a counter in pulse train generation  
mode or by using the frequency generator circuit.  
The frequency generator can output a square wave at many different  
frequencies. The frequency generator is independent of the two  
general-purpose 32-bit counter/timer modules on the NI cDAQ-9172  
chassis.  
Figure 39 shows a block diagram of the frequency generator.  
Frequency  
Output  
Timebase  
20 MHz Timebase  
100 kHz Timebase  
÷ 2  
Frequency Generator  
Freq Out  
Divisor  
(1–16)  
Figure 39. Frequency Generator Block Diagram  
The frequency generator generates the Frequency Output signal. The  
Frequency Output signal is the Frequency Output Timebase divided by a  
number you select from 1 to 16. The Frequency Output Timebase can be  
either the 20 MHz Timebase divided by 2 or the 100 kHz Timebase.  
The duty cycle of Frequency Output is 50% if the divider is either one or an  
even number. For an odd divider, suppose the divider is set to D. In this  
case, Frequency Output is low for (D + 1)/2 cycles and high for (D – 1)/2  
cycles of the Frequency Output Timebase.  
Figure 40 shows the output waveform of the frequency generator when the  
divider is set to 5.  
Frequency  
Output  
Timebase  
FREQ OUT  
(Divisor = 5)  
Figure 40. Frequency Generator Output Waveform  
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Frequency Output can be routed to any output PFI terminal. The FREQ  
OUT signal also can be routed to DO Sample Clock and DI Sample Clock.  
In software, program the frequency generator as you would program one of  
the counters for pulse train generation.  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
The counters can generate a signal with a frequency that is a fraction  
of an input signal. This function is equivalent to continuous pulse train  
generation.  
For information on connecting counter signals, refer to the Default  
Counter/Timer Routing section.  
Counter Timing Signals  
In slots 5 and/or 6 of the NI cDAQ-9172 chassis, you can configure  
C Series correlated digital input/output modules as one of the following  
counter timing signals:  
Counter n Source  
Counter n Gate  
Counter n Aux  
Counter n A  
Counter n B  
Counter n Z  
Counter n Up_Down  
Counter n HW Arm  
Counter n Internal Output  
Counter n TC  
Frequency Output  
In this section, n refers to either Counter 0 or 1. For example,  
Counter n Source refers to two signals—Counter 0 Source (the source  
input to Counter 0) and Counter 1 Source (the source input to Counter 1).  
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Counter n Source Signal  
The selected edge of the Counter n Source signal increments and  
decrements the counter value, depending upon the application the counter  
is performing. Table 6 lists how this terminal is used in various  
applications.  
Table 6. Counter Applications and Counter n Source  
Application  
Pulse Generation  
Purpose of Source Terminal  
Counter Timebase  
One Counter Time Measurements Counter Timebase  
Two Counter Time Measurements Input Terminal  
Nonbuffered Edge Counting  
Buffered Edge Counting  
Two-Edge Separation  
Input Terminal  
Input Terminal  
Counter Timebase  
Routing a Signal to Counter n Source  
Each counter has independent input selectors for the Counter n Source  
signal. You can route the following signals to the Counter n Source input:  
80 MHz Timebase  
20 MHz Timebase  
100 kHz Timebase  
Any PFI terminal  
Analog Comparison Event  
In addition, you can route Counter 1 TC or Counter 1 Gate to  
Counter 0 Source. You can also route Counter 0 TC or Counter 0 Gate to  
Counter 1 Source.  
Routing Counter n Source to an Output Terminal  
You can route Counter n Source to any output PFI terminal.  
Counter n Gate Signal  
The Counter n Gate signal can perform many different operations  
depending on the application including starting and stopping the counter,  
and saving the counter contents.  
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Routing a Signal to Counter n Gate  
Each counter has independent input selectors for the Counter n Gate signal.  
You can route the following signals to the Counter n Gate input:  
Any PFI terminal  
ai/ReferenceTrigger  
ai/StartTrigger  
ai/SampleClock  
ai/ConvertClock  
ao/SampleClock  
di/SampleClock  
do/SampleClock  
Change Detection Event  
Analog Comparison Event  
In addition, you can route Counter 1 Internal Output or Counter 1 Source  
to Counter 0 Gate. You can also route Counter 0 Internal Output or  
Counter 0 Source to Counter 1 Gate.  
Some of these options may not be available in some driver software.  
Routing Counter n Gate to an Output Terminal  
You can route Counter n Gate to any output PFI terminal.  
Counter n Aux Signal  
The Counter n Aux signal indicates the first edge in a two-signal  
edge-separation measurement.  
Routing a Signal to Counter n Aux  
Each counter has independent input selectors for the Counter n Aux signal.  
You can route the following signals to the Counter n Aux input:  
Any PFI terminal  
ai/ReferenceTrigger  
ai/StartTrigger  
Analog Comparison Event  
In addition, you can route Counter 1 Internal Output, Counter 1 Gate,  
Counter 1 Source, or Counter 0 Gate to Counter 0 Aux. You can also  
route Counter 0 Internal Output, Counter 0 Gate, Counter 0 Source, or  
Counter 1 Gate to Counter 1 Aux.  
Some of these options may not be available in some driver software.  
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Counter n A, Counter n B, and Counter n Z Signals  
Counter n B can control the direction of counting in edge counting  
applications. Use the A, B, and Z inputs to each counter when measuring  
quadrature encoders or measuring two pulse encoders.  
Routing Signals to A, B, and Z Counter Inputs  
Each counter has independent input selectors for each of the A, B, and Z  
inputs. You can route the following signals to each input:  
Any PFI terminal  
Analog Comparison Event  
Routing Counter n Z Signal to an Output Terminal  
You can route Counter n Z to any output PFI terminal.  
Counter n Up_Down Signal  
Counter n Up_Down is another name for the Counter n B signal.  
Counter n HW Arm Signal  
The Counter n HW Arm signal enables a counter to begin an input or output  
function.  
To begin any counter input or output function, you must first enable,  
or arm, the counter. In some applications, such as buffered semi-period  
measurement, the counter begins counting when armed. In other  
applications, such as single pulse-width measurement, the counter begins  
waiting for the Gate signal when it is armed. Counter output operations can  
use the arm signal in addition to a start trigger.  
Software can arm a counter or configure counters to be armed on a  
hardware signal. Software calls this hardware signal the Arm Start Trigger.  
Neutrally software routes the Arm Start Trigger to the Counter n HW Arm  
input of the counter.  
Routing Signals to Counter n HW Arm Input  
You can route the following signals to the Counter n HW Arm input:  
Any PFI terminal  
ai/ReferenceTrigger  
ai/StartTrigger  
Analog Comparison Event  
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You can route Counter 1 Internal Output to Counter 0 HW Arm. You can  
also route Counter 0 Internal Output to Counter 1 HW Arm.  
Some of these options may not be available in some driver software.  
Counter n Internal Output and Counter n TC Signals  
Counter n TC is an internal signal that asserts when the counter value is 0.  
The Counter n Internal Output signal changes in response to Counter n TC.  
The two software-selectable output options are pulse output on TC and  
toggle output on TC. The output polarity is software-selectable for both  
options.  
Routing Counter n Internal Output to an Output Terminal  
You can route Counter n Internal Output to any output PFI terminal.  
Frequency Output Signal  
The Frequency Output (FREQ OUT) signal is the output of the frequency  
output generator.  
Routing Frequency Output to a Terminal  
You can route Frequency Output to any output PFI terminal. The FREQ  
OUT signal can also route to DO Sample Clock and DI Sample Clock.  
Default Counter/Timer Routing  
Counter/timer signals are available to correlated digital I/O C Series  
modules in slots 5 and/or 6. To determine the signal routing options for  
modules installed in your system, refer to the Device Routes tab in MAX.  
Counter Triggering  
Counters support three different triggering actions—arm start, start, and  
pause.  
Arm Start Trigger  
To begin any counter input or output function, you must first enable, or  
arm, the counter. Software can arm a counter or configure counters to be  
armed on a hardware signal. Software calls this hardware signal the Arm  
Start Trigger. Internally, software routes the Arm Start Trigger to the  
Counter n HW Arm input of the counter.  
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For counter output operations, you can use the arm start trigger to have start  
trigger-like behavior. The arm start trigger can be used for synchronizing  
multiple counter input and output tasks.  
Start Trigger  
For counter output operations, you can configure a start trigger to begin  
a finite or continuous pulse generation. Once a continuous generation  
triggers, the pulses continue to generate until you stop the operation in  
software. For finite generations, the specified number of pulses is generated  
and the generation stops unless you use the retriggerable attribute. When  
you use this attribute, subsequent start triggers cause the generation to  
restart.  
When using a start trigger, the start trigger source routes to the  
Counter n Gate signal input of the counter.  
For counter input operations, the arm start trigger can imitate trigger-like  
behavior.  
Pause Trigger  
You can use pause triggers in edge counting and continuous pulse  
generation applications. For edge counting acquisitions, the counter stops  
counting edges while the external trigger signal is low and resumes when  
the signal goes high or vice versa. For continuous pulse generations, the  
counter stops generating pulses while the external trigger signal is low and  
resumes when the signal goes high or vice versa.  
When using a pause trigger, the pause trigger source routes to the  
Counter n Gate signal input of the counter.  
Other Counter Features  
Cascading Counters  
signals of each counter to the Gate inputs of the other counter. By cascading  
two counters together, you can effectively create a 64-bit counter. By  
cascading counters, you also can enable other applications. For example,  
to improve the accuracy of frequency measurements, use reciprocal  
frequency measurement, as described in the Method 3—Measure Large  
Range of Frequencies Using Two Counters section.  
Counter Filters  
You can enable a programmable debouncing filter on each PFI signal.  
When the filters are enabled, the NI cDAQ-9172 chassis samples the input  
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on each rising edge of a filter clock. The NI cDAQ-9172 chassis uses an  
onboard oscillator to generate the filter clock with a 40 MHz frequency.  
For more information, refer to the NI-DAQmx Help. The NI-DAQmx Help  
is available after installation from Start»Programs»National  
Instruments»NI-DAQ»NI-DAQmx Help.  
Note NI-DAQmx only supports filters on counter inputs.  
The following is an example of low to high transitions of the input signal.  
High to low transitions work similarly.  
Assume that an input terminal has been low for a long time. The input  
terminal then changes from low to high, but glitches several times. When  
the filter clock samples the signal high on N consecutive edges, the low to  
high transition is propagated to the rest of the circuit. The value of N  
depends on the filter setting, as listed in Table 7.  
Table 7. Counter Input Filters  
N (Filter Clocks  
Needed to  
Pass Signal)  
Pulse Width  
Guaranteed to  
Pass Filter  
Pulse Width  
Guaranteed to  
Not Pass Filter  
Filter Setting  
125 ns  
5
257  
125 ns  
6.425 µs  
2.56 ms  
100 ns  
6.400 µs  
2.54 ms  
6.425 µs  
2.56 ms  
~101,800  
Disabled  
You can configure the filter setting for each input independently. On power  
up, the filters are disabled. Figure 41 shows an example of a low to high  
transition on an input with its filter set to 125 ns (N = 5).  
Filtered input goes high  
when terminal is sampled  
PFI Terminal  
1
1
2
3
4
1
2
3
4
5
high on five consecutive  
filter clocks.  
Filter Clock  
(40 MHz)  
Filtered Input  
Figure 41. Filter Example  
Enabling filters introduces jitter on the input signal. For the 125 ns and  
6.425 µs filter settings, the jitter is up to 25 ns. On the 2.56 ms setting, the  
jitter is up to 10.025 µs.  
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Prescaling  
Prescaling allows the counter to count a signal that is faster than the  
maximum timebase of the counter. The NI cDAQ-9172 chassis offers 8X  
and 2X prescaling on each counter (prescaling can be disabled). Each  
prescaler consists of a small, simple counter that counts to eight (or two)  
and rolls over. This counter can run faster than the larger counters, which  
simply count the rollovers of this smaller counter. Thus, the prescaler acts  
as a frequency divider on the Source and puts out a frequency that is  
one-eighth (or one-half) of what it is accepting.  
External Signal  
Prescaler Rollover  
(Used as Source  
by Counter)  
Counter Value  
0
1
Figure 42. Prescaling  
Prescaling is intended for frequency measurement where the measurement  
is made on a continuous, repetitive signal. The prescaling counter cannot  
be read; therefore, you cannot determine how many edges have occurred  
since the previous rollover. You can use prescaling for event counting  
provided it is acceptable to have an error of up to seven (or one). You can  
use prescaling when the counter Source is an external signal. Prescaling  
is not available if the counter Source is one of the internal timebases  
(80MHzTimebase, 20MHzTimebase, or 100kHzTimebase).  
Duplicate Count Prevention  
Duplicate count prevention (or synchronous counting mode) ensures that a  
counter returns correct data in applications that use a slow or non-periodic  
external source. Duplicate count prevention applies only to buffered  
counter applications such as measuring frequency or period. In such  
buffered applications, the counter stores the number of times an external  
Source pulses between rising edges on the Gate signal.  
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Example Application That Works Correctly  
(No Duplicate Counting)  
Figure 43 shows an external buffered signal as the period measurement  
Source.  
Rising Edge  
of Gate  
Counter detects rising edge  
of Gate on the next rising  
edge of Source.  
Gate  
Source  
Counter Value  
Buffer  
6
7
1
2
1
7
2
7
Figure 43. Duplicate Count Prevention Example  
On the first rising edge of the Gate, the current count of seven is stored.  
On the next rising edge of the Gate, the counter stores a two because  
two Source pulses occurred after the previous rising edge of Gate.  
The counter synchronizes or samples the Gate signal with the Source  
signal, which means that the counter does not detect a rising edge in the  
Gate until the next Source pulse. In this example, the counter stores the  
values in the buffer on the first rising Source edge after the rising edge of  
Gate. The details of when exactly the counter synchronizes the Gate signal  
vary depending on the synchronization mode. Synchronization modes are  
described in the Synchronization Modes section.  
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Example Application That Works Incorrectly  
(Duplicate Counting)  
In Figure 44, after the first rising edge of Gate, no Source pulses occur,  
which means that the counter does not write the correct data to the buffer.  
No Source edge, so no  
value written to buffer.  
Gate  
Source  
Counter Value  
6
7
1
7
Buffer  
Figure 44. Duplicate Count Example  
Example Application That Prevents Duplicate Count  
With duplicate count prevention enabled, the counter synchronizes both the  
Source and Gate signals to the 80 MHz Timebase. By synchronizing to the  
timebase, the counter detects edges on the Gate even if the Source does not  
pulse. This enables the correct current count to be stored in the buffer even  
if no Source edges occur between Gate signals, as shown in Figure 45.  
Counter detects  
rising Gate edge.  
Counter value  
increments only  
one time for each  
Source pulse.  
Gate  
Source  
80 MHz Timebase  
Counter Value  
Buffer  
6
7
0
1
7
0
7
Figure 45. Duplicate Count Prevention Example  
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Even if the Source pulses are long, the counter increments only once for  
each Source pulse.  
Normally, the counter value and Counter n Internal Output signals change  
synchronously to the Source signal. With duplicate count prevention, the  
counter value and Counter n Internal Output signals change synchronously  
to the 80 MHz Timebase.  
Note Duplicate count prevention should only be used if the frequency of the Source signal  
is 20 MHz or less.  
When To Use Duplicate Count Prevention  
Use duplicate count prevention if the following conditions are true:  
You are making a counter measurement.  
You are using an external signal (such as PFI x) as the counter Source.  
The frequency of the external source is 20 MHz or less.  
You can have the counter value and output to change synchronously  
with the 80 MHz Timebase.  
In all other cases, you should not use duplicate count prevention.  
Enabling Duplicate Count Prevention in NI-DAQmx  
You enable duplicate count prevention in NI-DAQmx by setting the  
Enable Duplicate Count Prevention attribute/property. For specific  
information on finding the Enable Duplicate Count Prevention  
attribute/property, refer to the help file for the API you are using.  
Synchronization Modes  
The 32-bit counter counts up or down synchronously with the Source  
signal. The Gate signal and other counter inputs are asynchronous to the  
Source signal. The NI cDAQ-9172 chassis synchronizes these signals  
before presenting them to the internal counter.  
The NI cDAQ-9172 chassis uses one of three synchronization methods:  
80 MHz source mode  
Other internal source mode  
External source mode  
In NI-DAQmx, the chassis uses 80 MHz source mode if you perform the  
following:  
Perform a position measurement  
Select duplicate count prevention  
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Otherwise, the mode depends on the signal that drives Counter n Source.  
Table 8 describes the conditions for each mode.  
Table 8. Synchronization Mode Conditions  
Duplicate Count  
Prevention Enabled  
Type of  
Measurement  
Signal Driving  
Counter n Source  
Synchronization  
Mode  
Yes  
No  
No  
No  
Any  
Any  
80 MHz Source  
80 MHz Source  
80 MHz Source  
Other Internal Source  
Position Measurement Any  
Any  
80 MHz Timebase  
All Except Position  
Measurement  
20 MHz Timebase,  
100 kHz Timebase  
No  
All Except Position  
Measurement  
Any Other Signal  
(such as PFI)  
External Source  
80 MHz Source Mode  
In 80 MHz source mode, the NI cDAQ-9172 synchronizes signals on the  
rising edge of the source, and counts on the following rising edge of the  
source, as shown in Figure 46.  
Source  
Synchronize  
Count  
Figure 46. 80 MHz Source Mode  
Other Internal Source Mode  
In other internal source mode, the NI cDAQ-9172 chassis synchronizes  
signals on the falling edge of the source and counts on the following rising  
edge of the source, as shown in Figure 47.  
Source  
Synchronize  
Count  
Figure 47. Other Internal Source Mode  
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In external source mode, the chassis generates a delayed Source signal by  
delaying the Source signal by several nanoseconds. The NI cDAQ-9172  
chassis synchronizes signals on the rising edge of the delayed Source signal  
and counts on the following rising edge of the source, as shown in  
Figure 48.  
Source  
Synchronize  
Delayed Source  
Count  
Figure 48. External Source Model  
Digital Routing and Clock Generation  
The digital routing circuitry has the following functions:  
Manages the flow of data between the bus interface and the  
acquisition/generation sub-systems (analog input, analog output,  
digital I/O, and the counters). The digital routing circuitry uses FIFOs  
(if present) in each sub-system to ensure efficient data movement.  
Routes timing and control signals. The acquisition/generation  
sub-systems use these signals to manage acquisitions and generations.  
These signals can come from the following sources:  
Your C Series I/O modules  
User input through the PFI terminals using correlated digital  
C Series I/O modules in slots 5 and/or 6  
Routes and generates the main clock signals for the NI cDAQ-9172  
chassis.  
To determine the signal routing options for C Series I/O modules  
installed in the NI cDAQ-9172 chassis, refer to the Device Routes tab  
in MAX.  
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Clock Routing  
Figure 49 shows the clock routing circuitry of the NI cDAQ-9172 chassis.  
80 MHz Timebase  
Onboard  
80 MHz  
Oscillator  
20 MHz Timebase  
÷ 4  
100 kHz Timebase  
÷ 200  
Figure 49. NI cDAQ-9172 Clock Routing Circuitry  
80 MHz Timebase  
You can use the 80 MHz Timebase as the Source input to the 32-bit  
general-purpose counter/timers.  
The 80 MHz Timebase can be generated from the following sources:  
Onboard oscillator  
External signal (by using the external reference clock)  
20 MHz Timebase  
The 20 MHz Timebase normally generates many of the AI and AO timing  
signals. The 20 MHz Timebase can function as the Source input to the  
32-bit general-purpose counter/timers.  
The 20 MHz Timebase is generated by dividing down the  
80 MHz Timebase.  
100 kHz Timebase  
You can use the 100 kHz Timebase to generate many of the AI and AO  
timing signals. The 100 kHz Timebase can also function as the Source  
input to the 32-bit general-purpose counter/timers.  
The 100 kHz Timebase is generated by dividing down the 20 MHz  
Timebase by 200.  
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Specifications  
These specifications are for the NI cDAQ-9172 chassis only. These  
specifications are typical at 25 °C unless otherwise noted. For the C Series  
I/O module specifications, refer to the documentation for the C Series I/O  
modules you are using.  
Analog Input  
Input FIFO size ...................................... 2,047 samples  
Sample rate1  
Maximum........................................ 3.2 MS/s (multi-channel,  
aggregate)  
Minimum ........................................ 0 S/s  
Timing accuracy2 ................................... 50 ppm of sample rate  
Timing resolution2 ................................. 50 ns  
Number of channels supported .............. Determined by the C Series  
I/O modules  
Analog Output  
Numbers of channels supported  
In hardware-timed task ................... 16  
In non-hardware-timed task............ Determined by the C Series  
I/O modules  
Maximum update rate ............................ 1.6 MS/s (multi-channel,  
aggregate)  
Timing accuracy..................................... 50 ppm of sample rate  
Timing resolution................................... 50 ns  
Output FIFO size.................................... 8,191 samples shared among  
channels used  
1
Performance dependent on type of installed C Series I/O modules and number of channels in the task.  
Does not include group delay. Refer to C Series I/O module documentation for more information.  
2
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AO waveform modes..............................Non-periodic waveform,  
periodic waveform regeneration  
mode from onboard memory,  
periodic waveform regeneration  
from host buffer including  
dynamic update  
Digital Waveform Characteristics (Slots 1 through 4 Only)1  
Waveform acquisition (DI)  
FIFO........................................................2,047 samples  
Waveform generation (DO)  
FIFO........................................................2,047 samples  
Digital input sample clock frequency  
Streaming from application  
memory............................................0 to 8 MHz, system dependent  
Regenerate from FIFO.....................0 to 10 MHz  
Finite................................................0 to 10 MHz  
Digital output sample clock frequency  
Streaming from application  
memory............................................0 to 8 MHz, system dependent  
Regenerate from FIFO.....................0 to 10 MHz  
Finite................................................0 to 10 MHz  
Digital output or digital input  
sample clock source................................Any PFI, analog sample or  
convert clock, analog output  
sample clock, Ctr n Internal  
Output, and many other sources  
PFI Characteristics (Slots 5 and 6 Only)1  
Functionality...........................................Static digital input, static digital  
output, timing input, and timing  
output  
Timing output sources ............................Many analog input, analog  
output, counter, digital input, and  
digital output timing signals  
1
Requires correlated digital I/O modules installed on the appropriate slot(s).  
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Debounce filter settings ......................... Selectable per input:  
125 ns, 6.425 µs, 2.54 ms, disable,  
high and low transitions  
Timing input frequency.......................... 0 to 20 MHz  
Timing output frequency........................ 0 to 20 MHz  
General-Purpose Counter/Timers (Slots 5 and 6 Only)1  
Number of counter/timers ...................... 2  
Resolution .............................................. 32 bits  
Counter measurements........................... Edge counting, pulse,  
semi-period, period, two-edge  
separation  
Position measurements........................... X1, X2, X4 quadrature encoding  
with Channel Z reloading;  
two-pulse encoding  
Output applications ................................ Pulse, pulse train with dynamic  
updates, frequency division,  
equivalent time sampling  
Internal base clocks................................ 80 MHz, 20 MHz, 100 kHz  
External base clock frequency ............... 0 to 20 MHz  
Base clock accuracy............................... 50 ppm  
Output frequency.................................... 0 to 20 MHz  
Inputs...................................................... Gate, Source, HWarm, Aux, A, B,  
Z, Up_Down  
Routing options for inputs...................... Any PFI, analog trigger,  
many internal signals  
FIFO....................................................... 2 samples  
Data transfers ......................................... High-speed data stream,  
programmed I/O  
1
Requires correlated digital I/O modules installed in the appropriate slot(s).  
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Frequency Generator (Slots 5 and 6 Only)  
Number of channels................................1  
Base clocks .............................................10 MHz, 100 kHz  
Divisors...................................................1 to 16 (integers)  
Base clock accuracy................................50 ppm  
Output is available on any PFI terminal.  
External Digital Triggers (Slots 5 and 6 or with Some AI Modules)  
Source .....................................................Any PFI terminal  
Polarity....................................................Software-selectable for most  
signals  
Analog input function.............................Start Trigger, Reference Trigger,  
Pause Trigger, Sample Clock,  
Sample Clock Timebase  
Analog output function...........................Start Trigger, Pause Trigger,  
Sample Clock, Sample Clock  
Timebase  
Counter/timer functions..........................Gate, Source, HWarm, Aux, A, B,  
Z, Up_Down  
Module I/O States  
At power-on............................................Module-dependent. Refer to the  
documentation included with the  
C Series I/O module(s).  
When USB cable removed .....................Reverts to power-on state  
Power Requirements  
You must use a National Electric Code (NEC) Class 2 power source with  
the NI cDAQ-9172 chassis.  
Note Some I/O modules have additional power requirements. For more information about  
C Series I/O module(s) power requirements, refer to documentation included with the  
C Series I/O module(s).  
Note Sleep mode for C Series I/O modules is not supported in the NI cDAQ-9172.  
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Input voltage range................................. 11 V to 30 V  
Maximum required input power ............ 15 W  
Power input connector ........................... DC input jack with locking,  
threaded ring 0.8 in. (2 mm)  
center pin  
Power input mating connector ............... Switchcraft S760K  
Bus Interface  
USB specification .................................. USB 2.0 Hi-Speed  
Power from USB  
4.10 to 5.25 V ................................. 500 µA maximum  
High-performance data streams ............. 4  
Types available ............................... Analog input, analog output,  
digital input, digital output,  
counter/timer input  
Physical Characteristics  
If you need to clean the chassis, wipe it with a dry towel.  
Chassis weight (unloaded) ..................... Approx. 840 g  
(1 lb 13 oz)  
Chassis dimensions (unloaded).............. 25.4 cm × 8.89 cm × 5.84 cm  
(10.0 in. × 3.5 in. × 2.3 in.)  
Safety Standards  
The NI cDAQ-9172 chassis is designed to meet the requirements of the  
following standards of safety for electrical equipment for measurement,  
control, and laboratory use:  
IEC 61010-1, EN 61010-1  
UL 61010-1, CSA 61010-1  
Note For UL and other safety certifications, refer to the product label, or go to  
ni.com/certification, search by model number or product line, and click the  
appropriate link in the Certification column.  
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Environmental  
The NI cDAQ-9172 chassis is intended for indoor use only. For outdoor  
use, mount the system in a suitably rated enclosure.  
Operating temperature1  
(IEC-60068-2-1 and IEC-60068-2-2).....–20 to 55 °C  
Storage temperature  
(IEC-60068-2-1 and IEC-60068-2-2).....–40 to 85 °C  
Ingress protection ...................................IP 30  
Operating humidity (IEC-60068-2-56)...10 to 90% RH, noncondensing  
Storage humidity (IEC-60068-2-56) ......5 to 95% RH, noncondensing  
Maximum altitude...................................2,000 m  
Pollution Degree (IEC 60664)................2  
Shock and Vibration  
To meet these specifications, you must panel mount the NI cDAQ-9172  
system and affix ferrules to the ends of the terminal lines.  
Operational shock...................................30 g peak, half-sine, 11 ms pulse  
(Tested in accordance with  
IEC-60068-2-27. Test profile  
developed in accordance with  
MIL-PRF-28800F.)  
Random vibration  
Operating.........................................5 to 500 Hz, 0.3 grms  
Nonoperating...................................5 to 500 Hz, 2.4 grms  
(Tested in accordance  
with IEC-60068-2-64.  
Nonoperating test profile  
exceeds the requirements of  
MIL-PRF-28800F, Class 3.)  
1
When operated in temperatures below 0 °C, you must use the PS-5 power supply, or another power supply rated for below 0 °C.  
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Electromagnetic Compatibility  
This product is designed to meet the requirements of the following  
standards of EMC for electrical equipment for measurement, control,  
and laboratory use:  
EN 61326 EMC requirements; Minimum Immunity  
EN 55011 Emissions; Group 1, Class A  
CE, C-Tick, ICES, and FCC Part 15 Emissions; Class A  
Note For EMC compliance, operate this device according to product documentation.  
CE Compliance  
This product meets the essential requirements of applicable European  
Directives, as amended for CE marking, as follows:  
73/23/EEC; Low-Voltage Directive (safety)  
89/336/EEC; Electromagnetic Compatibility Directive (EMC)  
Note Refer to the Declaration of Conformity (DoC) for this product for any additional  
regulatory compliance information. To obtain the DoC for this product, visit ni.com/  
certification, search by model number or product line, and click the appropriate link  
in the Certification column.  
Waste Electrical and Electronic Equipment (WEEE)  
EU Customers At the end of their life cycle, all products must be sent to a WEEE recycling  
center. For more information about WEEE recycling centers and National Instruments  
WEEE initiatives, visit ni.com/environment/weee.htm.  
© National Instruments Corporation  
75  
NI cDAQ-9172 User Guide and Specifications  
Where to Go for Support  
National Instruments corporate headquarters is located at  
11500 North Mopac Expressway, Austin, Texas, 78759-3504.  
National Instruments also has offices located around the world to help  
address your support needs. For telephone support in the United States,  
create your service request at ni.com/support and follow the calling  
instructions or dial 512 795 8248. For telephone support outside the United  
States, contact your local branch office:  
Australia 1800 300 800, Austria 43 662 457990-0,  
Belgium 32 (0) 2 757 0020, Brazil 55 11 3262 3599,  
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Finland 385 (0) 9 725 72511, France 01 57 66 24 24,  
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Italy 39 02 413091, Japan 81 3 5472 2970, Korea 82 02 3451 3400,  
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New Zealand 0800 553 322, Norway 47 (0) 66 90 76 60,  
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Singapore 1800 226 5886, Slovenia 386 3 425 42 00,  
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Taiwan 886 02 2377 2222, Thailand 662 278 6777,  
Turkey 90 212 279 3031, United Kingdom 44 (0) 1635 523545  
NNational Instruments, NI, ni.com, and LabVIEW are trademarks of National Instruments Corporation.  
Refer to the Terms of Use section on ni.com/legal for more information about National  
Instruments trademarks. Other product and company names mentioned herein are trademarks or trade  
names of their respective companies. For patents covering National Instruments products, refer to the  
appropriate location: Help»Patents in your software, the patents.txt file on your CD, or  
ni.com/patents.  
© 2006–2007 National Instruments Corporation. All rights reserved.  
371747D-01  
Jun07  

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