B&B Electronics Strain Gauge/Load Cell Bridge Amplifier FBDA User manual

Documentation Number FBDA0797 Manual Cover Page
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
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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 [phone] -- FAX [phone]
Internet:
http://www.bb-elec.com
[e-mail]
[email protected].com
1997 B&B Electronics
Not Recommended for New Installations.
Please contact Technical Support for more information.

Documentation Number FBDA0797 Manual Table of Contents i
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
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TABLE OF CONTENTS
CHAPTER 1: INTRODUCTION.................................................................1
FEATURES ...............................................................................................1
PACKING LIST ..........................................................................................2
SOFTWARE ..............................................................................................2
CALIBRATION ...........................................................................................2
FBDA SPECIFICATIONS............................................................................2
CHAPTER 2: CONNECTIONS..................................................................3
POWER SUPPLY CONNECTIONS ................................................................3
SENSOR CONNECTIONS............................................................................3
DATA ACQUISITION CONNECTIONS............................................................4
CHAPTER 3: GAIN SELECTION..............................................................7
CHAPTER 4: EXCITATION VOLTAGE....................................................9

Documentation Number FBDA0797 Manual 1
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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

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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: 0.003V to 11VDC
Gain: 25, 40, 80, 220-1000
Maximum Gain Error: 5% of gain setting max.
Input Offset Voltage: 150µV max.
Input Offset Voltage Drift: 1.5µV/oC
Excitation Voltage: 0.5VDC to +11VDC
Operating Temperature Range: 0 to 70oC
Power Requirements: 13-18VDC @10mA (does
not include current draw
from excitation voltage.)

Documentation Number FBDA0797 Manual 3
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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.
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.
Table 2.1: Terminal Block Assignments
Terminal
Block Name Function I/O
SIG+ Positive Signal Lead Input
SIG- Negative Signal Lead Input
EXV Excitation Voltage Output
A/D 1 A/D Converter channel Input
+13V Power Supply Connection Input
GND Power Supply Connection Input

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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.
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.
Table 2.2: DB-25 (Male) Pin Assignments
DB-25 Pin # Function DB-25 Pin # Function
1 GND 14 -------
2 ------- 15 -------
3 ------- 16 -------
4 ------- 17 looped to 18
5 ------- 18 looped to 17
6 ------- 19 GND
7 GND 20 -------
8 Vout 21 -------
9 A/D 1 22 -------
10 ------- 23 -------
11 ------- 24 -------
12 ------- 25 -------
13 -------

Documentation Number FBDA0797 Manual 5
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Figure 2.1: Block Diagram of FBDA Connections
A/D
Note: Conditioned signal is
available on DB-25 pin #8
6
4
5
Terminal Blocks
2
3
1
+13V
A/D 1 +13V REF+
GNDGND
19 19
REF-
DB-25P Connector
GND
GND
Vout
Module
FBDA
EXV
SIG-
SIG+
88
99
17
18
17
18
A/D 1
+5V
A/D 0
7
1
GND
7
GND
1
Sensor
and is labeled as Vout.
Module

Documentation Number FBDA0797 Manual 7
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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.
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.
Table 3.1: Jumper Selection to Choose Gain
Gain Jumper Selection
25 Jumper pin 5 to pin 6
40 Jumper pin 4 to pin 5
80 Jumper pin 2 to pin 3
220-1000 Jumper pin 1 to pin 2

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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.
Gain Equation
GAIN = Vout / ((SIG+) - (SIG-))

Documentation Number FBDA0797 Manual 9
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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.