BB Electronics Stereo Amplifier FBDA User Manual

Not Recommended for New Installations.  
Please contact Technical Support for more information.  
Strain Gauge/Load Cell Bridge Amplifier  
Model FBDA  
Documentation Number FBDA0797  
This product  
Designed and Manufactured  
In Ottawa, Illinois  
USA  
of domestic and imported parts by  
B&B Electronics Mfg. Co. Inc.  
707 Dayton Road -- P.O. Box 1040 -- Ottawa, IL 61350  
PH (815) 433-5100 -- FAX (815) 433-5105  
Internet:  
1997 B&B Electronics  
Documentation Number FBDA0797 Manual  
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350  
Cover Page  
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Chapter 1: Introduction  
Features  
The FBDA is a signal conditioning module that allows you to  
measure voltages produced by full-bridge sensors using a data  
acquisition module. This module can condition signals from Strain  
Gauges, Load Cells, Pressure Sensors, and other Full-Bridge  
Transducer Sensors. A number of different gain settings are  
available on the FBDA to accommodate a wide variety of voltage  
ranges. The FBDA also provides an adjustable excitation voltage for  
the full-bridge circuitry. The sensor connections are made using  
terminal blocks, and the A/D connections are made through a DB-25  
connector. B&B Electronics’ SDAXX, and ADIO12 data acquisition  
modules are pin compatible with the FBDA. This allows you to  
simply plug one of the data acquisition modules mentioned above  
into the FBDA, and the A/D connections are complete. The SPDA  
data acquisition modules can also be used with the FBDA.  
Figure 1.1: FBDA Module  
Documentation Number FBDA0797 Manual  
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Packing List  
Examine the shipping carton and the contents for physical  
damage. The following items should be in the shipping carton:  
1. FBDA module  
2. This instruction manual  
If any of these items are damaged or missing, contact B&B  
Electronics immediately.  
Software  
Software is not included with the FBDA module. This device is  
used in conjunction with a data acquisition device. All of B&B  
Electronics’ data acquisition modules come complete with software  
that you can modify to meet your exact needs.  
Calibration  
The FBDA is calibrated at the factory. The excitation  
voltage is set to 5VDC ± 0.05VDC and the gain is calibrated at 80 ±  
2. The process of calibrating the FBDA and your sensor will vary  
depending on the type of sensor being used. An example calibration  
procedure is covered in Chapter 3.  
FBDA Specifications  
Size:  
4.8 x 2.2 x 0.9 in  
Maximum Input Voltage from Sensor: 440mV (using Gain = 25)  
Output Voltage Range:  
Gain:  
Maximum Gain Error:  
Input Offset Voltage:  
Input Offset Voltage Drift:  
Excitation Voltage:  
0.003V to 11VDC  
25, 40, 80, 220-1000  
5% of gain setting max.  
150µV max.  
1.5µV/oC  
0.5VDC to +11VDC  
Operating Temperature Range:  
Power Requirements:  
0 to 70oC  
13-18VDC @10mA (does  
not include current draw  
from excitation voltage.)  
2
Documentation Number FBDA0797 Manual  
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350  
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Chapter 2: Connections  
Power Supply Connections  
The FBDA module requires 13 to 18VDC @ 10mA. Model  
232PS2 available from B&B Electronics is recommended. Although  
the 232PS2 is a 12VDC power supply, it outputs a voltage above  
13VDC when less than 10mA are being drawn from it. The power  
supply is connected to the terminal blocks marked +13V and GND.  
Make sure the polarity of the power supply is correct (the white  
striped wire on the 232PS2 is the positive lead).  
Sensor Connections  
Most full-bridge sensor circuits require four connections for the  
sensor to operate properly. These connections will be made using  
the terminal blocks. First, an excitation voltage is required to excite  
the bridge circuitry. This can be done using the adjustable excitation  
voltage (marked EXV) available on the FBDA, or another voltage  
source can be furnished by the user. This excitation voltage is  
referenced with respect to ground, which is the second connection  
(marked GND). The remaining two leads from the sensor carry the  
differential signal voltage that is to be conditioned and read by the  
data acquisition module. These two leads are connected to SIG+  
and SIG-. Consult your sensor manual to determine the signal lead  
polarity. Table 2.1 shows the terminal block assignments.  
Table 2.1: Terminal Block Assignments  
Terminal  
Block Name  
SIG+  
Function  
I/O  
Positive Signal Lead  
Negative Signal Lead  
Excitation Voltage  
Input  
Input  
Output  
Input  
Input  
Input  
SIG-  
EXV  
A/D 1  
+13V  
A/D Converter channel  
Power Supply Connection  
Power Supply Connection  
GND  
Note: A/D 1 is connected straight through from the terminal blocks  
to DB-25 pin # 9. This allows access to A/D channel 1 on B&B  
Electronic’s SDAXX line of A/D converters. This channel can read  
voltages between 0 and 5VDC (useful for calibrating the excitation  
voltage). This channel has no signal conditioning circuitry. It is  
simply connected to A/D 1 on the data acquisition module.  
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Data Acquisition Connections  
The connections to the Data Acquisition Module are made  
through a DB-25 (male) connector. The FBDA is pin compatible with  
B&B Electronics’ SDAXX, and ADIO12 modules. This allows you to  
simply plug the FBDA into one of the above data acquisition  
modules, and the data acquisition module connections to the FBDA  
are complete. Table 2.2 contains the DB-25 (male) pin  
assignments.  
Table 2.2: DB-25 (Male) Pin Assignments  
DB-25 Pin #  
Function  
GND  
DB-25 Pin #  
Function  
-------  
-------  
1
2
3
4
5
6
7
8
9
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
-------  
-------  
-------  
-------  
-------  
GND  
-------  
looped to 18  
looped to 17  
GND  
-------  
-------  
-------  
-------  
-------  
-------  
Vout  
A/D 1  
-------  
-------  
-------  
-------  
1. ------- denotes no connection.  
2. The conditioned sensor signal is available on pin #8 and is  
labeled Vout.  
3. Pin #9 is connected straight through to terminal block A/D 1 (no  
signal conditioning circuitry).  
4. Pins #17 and #18 are looped to each other to provide +5V to  
REF+ in the SDAXX line of A/D modules.  
5. Pin #19 provides 0V to REF- in the SDAXX line of A/D modules.  
Figure 2.1 contains a diagram of the connections required to read  
the signal produced by a sensor.  
4
Documentation Number FBDA0797 Manual  
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Note: Conditioned signal is  
available on DB-25 pin #8  
and is labeled as Vout.  
Sensor  
Terminal Blocks  
DB-25P Connector  
1
2
3
1
1
7
SIG-  
SIG+  
EXV  
GND  
GND  
Vout  
GND  
GND  
A/D 0  
A/D 1  
+5V  
7
8
8
FBDA  
Module  
9
9
4
5
6
17  
18  
19  
17  
18  
19  
A/D 1  
+13V  
+13V  
GND  
REF+  
REF-  
GND  
Figure 2.1: Block Diagram of FBDA Connections  
Documentation Number FBDA0797 Manual  
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Chapter 3: Gain Selection  
The FBDA has several different gain settings to provide the  
largest possible voltage range for an A/D converter. The gain of the  
FBDA is selected using a jumper, 6 jumper pins (labeled 1-6), and a  
potentiometer (labeled P1). The FBDA is calibrated at the factory to  
have a gain of 80 ± 2. To change the gain of the FBDA the  
following steps should be followed:  
1. Remove the cover from the FBDA using a small slotted  
screwdriver.  
2. There are six jumper pins labeled 1-6. Place the jumper on the  
two pins selected from Table 3.1 below. Placing the jumper on  
the two selected pins will set a gain near the values listed in  
Table 3.1.  
3. Make all of the required connections (power supply, A/D  
converter, sensor, and excitation voltage), and turn on the  
power.  
4. Set up your sensor to provide a known input signal for the  
FBDA. If you are using a load cell, place a known weight on the  
load cell. This will produce a known input signal.  
5. The output voltage from the FBDA can be read from DB-25 pin 8  
(A/D 0 on B&B Electronics’ SDAXX data acquisition modules).  
6. Adjust P1 to trim the gain to an exact value. The gain equation  
is shown below. ((SIG+) - (SIG-)) is the input signal.  
Table 3.1: Jumper Selection to Choose Gain  
Gain  
25  
40  
80  
220-1000  
Jumper Selection  
Jumper pin 5 to pin 6  
Jumper pin 4 to pin 5  
Jumper pin 2 to pin 3  
Jumper pin 1 to pin 2  
1. The potentiometer (P1) becomes more critical as the gain is  
increased.  
2. The gain range of 220 to 1000 is entirely decided by P1. When  
P1 is turned completely in counter-clock-wise, the Gain will be  
close to 220. When P1 is turned completely clock-wise, the  
Gain will be greater than 1000.  
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Gain Equation  
GAIN = Vout / ((SIG+) - (SIG-))  
Sensors that incorporate bridge circuitry usually have  
noticeable zero offsets. This should be considered when taking  
measurements and determining gain. The easiest way to solve this  
problem is to calibrate the system while avoiding zero inputs, and  
correct for the zero offset in software.  
Example:  
If a 10lb. load cell needs to be calibrated, the suggested method  
is the following:  
1. Make all of the required connections.  
2. Place a 1lb. mass on the load cell. Record the voltage on DB-  
25 pin 8 as Vouta. Pin 8 is A/D 0 on the SDAXX modules.  
3. Add a second 1lb. mass onto the load cell. Record the voltage  
on DB-25 pin 8 as Voutb.  
4. Subtract Vouta form Voutb. The difference is the voltage, Vout,  
which corresponds to 1lb.  
5. Calculate what ((SIG+) - (SIG-)) is for 1lb. This is the voltage  
produced by the sensor.  
6. Use the Gain Equation to calculate the exact gain of the  
amplifier.  
7. Adjust P1, and repeat process until the desired gain is achieved.  
8. Subtract Vouta from Vout. The difference is the zero offset  
error. The zero offset error should be included in any equation  
conversion equation used in your software.  
8
Documentation Number FBDA0797 Manual  
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350  
PH (815) 433-5100 -- FAX (815) 433-5105  
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Chapter 4: Excitation Voltage  
Sensors that are based on a Wheatstone bridge need an  
excitation voltage to excite the bridge. The FBDA provides an  
adjustable excitation voltage. This excitation voltage is available on  
the terminal block labeled EXV. The excitation voltage is set to  
5VDC ± 0.05VDC at the factory. This voltage is referenced with  
respect to GND. To adjust the excitation voltage, the following steps  
should be followed:  
1. Remove the cover from the FBDA module using a small slotted  
screwdriver.  
2. Make all of the required connections except the sensor  
connections and turn on the power.  
3. Using a voltmeter, measure the voltage on the terminal block  
labeled EXV with respect to the GND terminal block. Adjust P2  
to change the excitation voltage. The terminal block labeled A/D  
1 can be used to measure the excitation voltage.  
Sensors that are comprised of Wheatstone bridges usually state  
the amount of output per volt of excitation voltage. An example is:  
10mV output / 1V of excitation. If a 5V excitation voltage is used,  
The full scale output of the sensor will be 50mV. The gain of the  
FBDA should then be chosen, so that Vout does not exceed 5V (the  
maximum voltage that the SDAXX line of data acquisition modules  
can measure).  
If for some reason the excitation voltage source in the FBDA  
does not meet your needs, you can use an external excitation  
voltage. If this is the case, then nothing should be connected to the  
EXV terminal block, and the GND lead of the external excitation  
voltage source should be connected to the GND terminal block on  
the FBDA module.  
Documentation Number FBDA0797 Manual  
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