National Instruments Car Stereo System SCXI 1125 User Manual

CALIBRATION PROCEDURE  
SCXI -1125  
Introduction  
This document contains information and step-by-step instructions for  
verifying and calibrating the National Instruments SCXI-1125 signal  
conditioning module.  
What Is Calibration?  
Calibration is a procedure of reading offset and gain errors from a device  
and updating special analog calibration circuitry that corrects these errors.  
National Instruments calibrates every SCXI-1125 module at the factory.  
During the factory calibration process, the calibration constants are stored  
in the non-volatile memory of the device. These values are loaded from  
memory and used as needed by the device.  
Why Should You Calibrate?  
Offset and gain errors drift with time and temperature changes, which could  
invalidate the factory-set calibration of a device and increase measurement  
uncertainty. Calibration restores the device to its specified accuracy.  
How Often Should You Calibrate?  
The measurement accuracy requirements of your application  
determine how often you should calibrate your SCXI-1125 module.  
National Instruments recommends you perform a complete calibration  
at least once every year. You can shorten this interval to six months or  
90 days, based on the demands of your application.  
CVI, LabVIEW, National Instruments, ni.com, NI-DAQ, and SCXIare trademarks of National Instruments Corporation. Product and company  
names mentioned herein are trademarks or trade names of their respective companies.  
370271A-01  
© Copyright 2000 National Instruments Corp. All rights reserved.  
December 2000  
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Documentation  
The NI-DAQ Function Reference Online Help file and NI-DAQ User  
Manual for PC Compatibles contain detailed information on using the  
NI-DAQ driver. The function reference online help file includes detailed  
information on the driver functions. You can access the online help by  
clicking Start»Programs»National Instruments DAQ»NI-DAQ Help.  
The user manual provides instructions on installing and configuring  
National Instruments DAQ devices. This manual also includes detailed  
information on creating applications that use the NI-DAQ driver. These are  
your primary references for writing your calibration utility. For further  
information on the products you are calibrating, refer to your device user  
manuals.  
Test Conditions  
Follow these guidelines to optimize the connections and the environment  
during calibration:  
Keep connections to the SCXI module short. Long cables and wires act  
as antennae, picking up extra noise and thermal offsets that can affect  
measurements.  
Use shielded copper wire for all cable connections to the device.  
Use twisted-pair wire to eliminate noise and thermal offsets.  
Maintain the temperature between 18 and 28 °C.  
Keep relative humidity below 80%.  
Allow a warm-up time of at least 15 minutes for the SCXI module and  
30 minutes for the E Series device to ensure the measurement circuitry  
is at a stable operating temperature.  
Calibration  
The calibration process consists of the following steps:  
1. Setting up the device for testing.  
2. Verifying the existing operation of the device to determine whether it  
is operating within its specifications.  
3. Adjusting the device with respect to a known voltage source.  
4. Verifying that the device is operating within its specifications after  
adjustments.  
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SCXI-1125 Calibration Procedure  
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Setting Up Your Module  
Complete the following steps to set up your module for testing:  
1. Install the SCXI-1125 in slot 1 of the SCXI chassis.  
2. Connect a 68-to-68-pin cable between the SCXI module and the  
E Series DAQ device installed in the host computer.  
3. Configure the hardware with Measurement & Automation Explorer  
(MAX). For more information on configuring the system, refer to the  
E Series device and SCXI module documentation.  
Verifying Gain and Offset Errors  
The verification procedure determines how well the SCXI-1125 module is  
meeting its specifications. You can use this information to select the  
appropriate calibration interval for your application.  
Complete the following steps to verify gain and offset errors in the  
SCXI-1125:  
1. Read the Test Conditions section earlier in this document.  
2. Refer to the specifications in Table 1 at the end of this document.  
3. Connect the E Series device to the SCXI-1125.  
4. Call Calibrate_E_Seriesto minimize the uncertainty associated  
with the E Series device measurements. Set the following parameters:  
deviceNumberThe value assigned by MAX  
calOpND_SELF_CALIBRATE  
setOfCalConstantsND_USER_EEPROM_AREA  
calRefVolts0.0  
5. Call AI_Configureto put the E Series device in bipolar mode. Set the  
following parameters:  
deviceNumberThe value assigned by MAX  
chan0  
inputMode0  
inputRange0  
polarity0  
driveAIS0  
6. Call MIO_Configto enable dithering on the E Series device. Set the  
following parameters:  
deviceNumberThe value assigned by MAX  
dither1  
useAMUX0  
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7. Connect the calibrator to the appropriate analog input, starting  
with channel 0. Refer to Figure 1 to determine which pins on the  
96-pin front connector correspond to the positive and negative inputs  
of the specified channel. For example, the positive input for channel 0  
(CH0+) is pin A32. The negative input for channel 0 (CH0) is pin  
C32. If you are using an SCXI-1320 terminal block connected to the  
SCXI-1125, connect the calibrator to the CH0+ and CH0inputs.  
8. Call SCXI_Single_Chan_Setupto configure the module for  
single-channel measurements. Set the following parameters:  
SCXIchassisIDThe value assigned by MAX  
moduleSlot1  
moduleChanThe same channel number from step 7  
DAQdeviceNumberThe device number assigned by MAX for  
the E Series DAQ device  
9. Call SCXI_Set_Gainto set the gain you want to test on the module.  
Set the following parameters:  
SCXIchassisIDThe ID obtained when the chassis is configured  
with MAX  
moduleSlot1  
channelThe channel number from step 7  
gainThe first gain value you want to testyou can find this  
gain value in Table 1.  
10. Call SCXI_Configure_Filterto configure the filter setting on the  
module. Set the following parameters:  
SCXIchassisIDThe ID obtained when the chassis is configured  
with MAX  
moduleSlot1  
channelThe channel number from step 7  
filterMode1  
cutoffFrequency10,000  
11. Set the calibrator to output the test point voltage from Table 1.  
12. Call DAQ_Op. Set the following parameters:  
deviceNumberThe device number of the DAQ device  
channel0  
gain1 for 16-bit E Series devices or 1 for 12-bit E Series  
devices  
count5,000  
sampleRate10,000  
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13. Call SCXI_Scale. Set the following parameters:  
SCXIChassisIDThe value assigned by MAX  
moduleSlot1  
channelThe same channel number from step 7  
SCXIgainThe same gain value from step 9  
TBgain1  
DAQboardThe device number for the DAQ device  
DAQChannel0  
DAQgain1 for 16-bit devices, 1 for 12-bit devices  
numPoints5.000  
binArrayThe array returned from the DAQ_Opfunction  
The result is a set of scaled voltages that you read from the SCXI  
module.  
14. Average the results returned from the SCXI_Scalefunction. Compare  
the averaged result to the upper and lower limits in Table 1. If the result  
falls within these limits, your module has passed this portion of the  
test. If it does not, your module needs to be adjusted using the steps in  
the next section, Adjusting for Gain and Offset Errors.  
15. Repeat steps 8 through 14 for the remaining gains.  
16. Repeat steps 7 through 15 for the remaining channels.  
You have now finished verifying your SCXI-1125.  
Note If all channels fall within the upper and lower limits, your device does not need to  
be adjusted.  
Adjusting for Gain and Offset Errors  
The following two sections explain how to determine the gain and offset  
errors of your SCXI-1125 and how to adjust the calibration constants to  
correct for these errors.  
Determining Gain and Offset Errors  
Complete the following steps to determine the gain and offset errors of the  
SCXI-1125:  
1. Read the Test Conditions section.  
2. Connect the E Series device to the SCXI-1125.  
3. Call Calibrate_E_Seriesto minimize the uncertainty associated  
with the E series device measurements. Set the following parameters:  
deviceNumberThe value assigned by MAX  
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calOpND_SELF_CALIBRATE  
setOfCalConstantsND_USER_EEPROM_AREA  
calRefVolts0.0  
4. Call AI_Configureto put the E Series device in bipolar mode. Set the  
following parameters:  
deviceNumberThe value assigned by MAX  
chan0  
inputMode0  
inputRange0  
polarity0  
driveAIS0  
5. Call MIO_Configto enable dithering on the E Series device. Set the  
following parameters:  
deviceNumberThe value assigned by MAX  
dither1  
useAMUX0  
6. Call SCXI_Single_Chan_Setupto configure the module for  
single-channel measurements. Set the following parameters:  
SCXIchassisIDThe value assigned by MAX  
moduleSlot1  
moduleChanThe channel you want to adjust  
DAQdeviceNumberThe device number assigned by MAX for  
the E Series DAQ device  
7. Call SCXI_Set_Gain. Set the following parameters:  
SCXIchassisIDThe ID of the SCXI chassis obtained when you  
configure the chassis with MAX  
moduleSlot1, because the SCXI-1125 should be installed in  
slot 1  
channelThe same channel number from step 6  
gainThe gain value you want to adjust. Refer to Table 1 for  
acceptable gain values  
8. Call SCXI_Configure_Filterto configure the filter setting on the  
module. Set the following parameters:  
SCXIchassisIDThe ID of the SCXI chassis obtained when you  
configure the chassis with MAX  
moduleSlot1  
channelThe same channel number from step 7  
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filterMode1  
cutoffFrequency10,000  
9. Connect the calibrator to the analog input you want to adjust. Refer  
to Figure 1 to determine the pins on the 96-pin front connector that  
correspond to the positive and negative inputs of the specified channel.  
For example, the positive input for channel 0 is pin A32, which is  
labeled CH0+. The negative input for channel 0 is pin C32, which  
is labeled CH0. If you are using an SCXI-1320 terminal block  
connected to the SCXI-1125, connect the calibrator to the CH0+  
and CH0inputs.  
10. Connect the DMM to the positive output on pin 3 (MCH0+) and  
negative output on pin 4 (MCH0) on the rear panel connector.  
Figure 2 shows the 50-pin rear panel connector.  
Tip For easy access to individual pins, use a screw terminal adapter connected to a  
50-pin terminal block.  
11. Set the calibrator voltage to the positive test point value in Table 1.  
12. Read the voltage from the DMM. Record the actual DMM reading,  
which is output1, and the calibrator output voltage, which is volt1, for  
later use.  
13. Set the calibrator to the negative test point value for the same gain.  
Skip any input limits that are specified as 0.0 V. You need only upper  
and lower limits for adjustment.  
14. Read the voltage from the DMM. Record the actual DMM reading,  
output2, and the calibrator output voltage, voltage2.  
You now have two pairs of data points, (volt1, output1) and (volt2,  
output2), where volt is the calibrator reading and output is the DMM  
reading.  
15. Convert the DMM voltage readings (output1 and output2) to binary  
readings (binary1 and binary2) by using one of the following  
equations:  
output  
20  
× 212  
----------------  
binary reading for 12-bit E Series products (binary) =  
output  
----------------  
20  
binary reading for 16-bit E Series products (binary)=  
× 216  
For example, using a 12-bit product such as a PCI-MIO-16E-1 and  
obtaining a DMM reading of 9.9 V, you would have the following  
results:  
binary reading = (9.9/20) × 212 = 2027.52  
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16. Record binary1 with volt1 and binary2 with volt2 for later use.  
17. Repeat steps 7 through 16 for the remaining gain values you want to  
adjust on this channel.  
18. Repeat steps 6 through 17 for the remaining channels you want to  
adjust.  
You have determined the new calibration constants. Use these values in the  
the following section, Adjusting Calibration Constants.  
Adjusting Calibration Constants  
Complete the following steps to adjust the calibration constants on the  
SCXI-1125:  
1. Call SCXI_Cal_Constantsto create and store the new calibration  
constants in the SCXI-1125 memory. Set the following parameters:  
SCXIchassisIDThe ID assigned by MAX  
ModuleSlot1, because the SCXI-1125 should be installed in  
slot 1  
channelThe channel on the SCXI-1125 you want to adjust  
OpCode2  
calibrationArea0  
rangeCode0 (not used for the SCXI-1125)  
SCXIgainThe gain you want to adjust  
DAQboardThe device number assigned by MAX  
DAQChan0  
DAQGain1 for 16-bit devices, 1 for 12-bit devices  
Tbgain1.0  
volt1 and volt2The first and second voltage readings for the  
gain values that you are about to save on the SCXI-1125  
binary1 and binary2The first and second binary readings for  
the gain values that you are about to save on the SCXI-1125  
calConst1 and calConst2These are return values  
2. Repeat step 1, changing calibrationArea to 1.  
3. Repeat steps 1 and 2 for the next channel.  
You have now finished adjusting the calibration constants of your  
SCXI-1125.  
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SCXI-1125 Calibration Procedure  
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Verifying Adjusted Values  
After completing the adjustments to your SCXI-1125 module, it is  
important that you verify the analog input operation by repeating the steps  
listed in the Verifying Gain and Offset Errors section of this document.  
Reverifying after adjustments ensures that your SCXI-1125 module is now  
operating within its specifications.  
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Front and Rear Signal Connector Diagrams  
A
B
C
32  
32  
CH0+  
CH1+  
CH0–  
CH1–  
NC  
30  
28  
26  
24  
22  
20  
18  
16  
14  
12  
10  
8
30  
28  
NC  
CH2+  
CH3+  
26 CH2–  
24 CH3–  
22  
20 CH4–  
NC  
NC  
CH4+  
CH5+  
18  
16  
CH5–  
NC  
NC  
CH6+  
14 CH6–  
12 CH7–  
CH7+  
NC  
NC  
10  
8
RSVD  
RSVD  
CJTEMP  
RSVD  
RSVD  
RSVD  
+5 V  
6
6
4
4
CHSGND  
2
2
This symbol indicates that no physical pin is present  
Figure 1. Front Signal Connector Pin Assignments  
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AOGND  
MCH0+  
MCH1+  
MCH2+  
MCH3+  
1
3
5
7
9
2
4
6
8
AOGND  
MCH0  
MCH1–  
MCH2–  
10 MCH3–  
MCH4+ 11 12 MCH4–  
MCH5+ 13 14 MCH5–  
15 16  
MCH6–  
MCH6+  
MCH7+ 17 18 MCH7–  
OUTREF 19 20  
21 22  
23 24  
DIGGND  
SERDATIN 25 26 SERDATOUT  
DAQD*/A 27 28  
SLOT0SEL* 29 30  
31 32  
DIGGND 33 34  
SCANCLK  
35 36  
SERCLK 37 38  
39 40  
41 42  
43 44  
45 46  
SYNC  
47 48  
49 50  
Figure 2. Rear Signal Connector Pin Assignments  
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Specifications  
The following table contains the specifications you should use when  
verifying and calibrating your SCXI-1125 module. If your device has been  
calibrated within the last year, the test point value should fall between the  
Upper Limit and Lower Limit values.  
Table 1. SCXI-1125 Specifications at 25 °C 10 °C  
Gain  
1
Range  
5
Test Point  
4.950000  
0.000000  
4.950000  
2.475000  
0.000000  
2.475000  
0.990000  
0.000000  
0.990000  
0.495000  
0.000000  
0.495000  
0.247500  
0.000000  
0.247500  
0.099000  
0.000000  
0.099000  
0.0495000  
0.000000  
0.049500  
0.024750  
0.000000  
Upper Limit (V)  
4.9623181  
0.005002  
Lower Limit (V)  
4.9376819  
0.005002  
4.9623181  
2.4688400  
0.002502  
2.4811601  
0.9875348  
0.001002  
0.9924652  
0.4937664  
0.000502  
0.4962336  
0.24688220  
0.000252  
0.24811781  
0.09875168  
0.000102  
0.09924832  
0.04937484  
0.000052  
0.04962516  
0.02468642  
0.000027  
1
0
1
5  
4.9376819  
2.4811601  
0.002502  
2
2.5  
0
2
2
2.5  
1
2.4688400  
0.9924652  
0.001002  
5
5
0
5
1  
0.9875348  
0.4962336  
0.000502  
10  
10  
10  
20  
20  
20  
50  
50  
50  
100  
100  
100  
200  
200  
0.5  
0
0.5  
0.25  
0
0.4937664  
0.24811781  
0.000252  
0.25  
0.1  
0
0.24688220  
0.09924832  
0.000102  
0.1  
0.05  
0
0.09875168  
0.04962516  
0.000052  
0.05  
0.025  
0
0.04937484  
0.02481358  
0.000027  
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Table 1. SCXI-1125 Specifications at 25 °C 10 °C (Continued)  
Gain  
200  
Range  
0.025  
0.02  
0
Test Point  
0.024750  
0.019800  
0.000000  
0.019800  
0.009900  
0.000000  
0.009900  
0.00495  
Upper Limit (V)  
0.02468642  
0.01985126  
0.000022  
Lower Limit (V)  
0.02481358  
0.01974874  
0.000022  
250  
250  
250  
0.02  
0.01  
0
0.01974874  
0.00992663  
0.000012  
0.01985126  
0.00987337  
0.000012  
500  
500  
500  
0.01  
0.005  
0
0.00987337  
0.00496432  
0.000007  
0.00992663  
0.00493568  
0.000007  
1000  
1000  
1000  
2000  
2000  
2000  
0.000000  
0.004950  
0.002475  
0.000000  
0.002475  
0.005  
0.0025  
0
0.00493568  
0.00248316  
0.000005  
0.00496432  
0.00246684  
0.000005  
0.0025  
0.00246684  
0.00248316  
Limits Valid for 4 Hz or 10 kHz Filter Settings  
Valid when using an MIO device after performing an MIO internal calibration.  
Valid for both filter settings with 5.000 point averaging at 10,000 samples per second.  
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