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2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
1
eco# 040325-2, 4/2001
Model 433 Bridgesensor
Features
Complete Strain Gage Bridge Signal Conditioner
Isolated 4-20 mA or 0-20 mA Output
Output Capable of Driving 1000 ohm Loop
Bridge Balance with 80% Tare Offset Capability
High Gain Amplifier; Can Accept Full Scale Live
Load Signals as Low as 5 mV and Provide 16 mA
Output Span
Excitation Supply Capable of Driving
Four Load Cells
AC Powered
Rugged Epoxy Encapsulated Design
Applications
Weighing with Load Cells
Process Control Add-on Loops
Can Be Used With All Types of
Low Output Sensors
Description
The Model 433 is a self contained, AC powered signal
conditioner for bridge type instrumentation. It contains a
precision instrumentation amplifier with isolated, filtered output
and a highly regulated, low noise, adjustable output bridge
excitation source. The unit is completely encapsulated for
use in rugged environments.
433 Block Diagram
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
2
Model 433 Bridgesensor
eco# 040325-2, 4/2001
Specifications
NOTE: Unless otherwise noted, specifications apply after one hour
warm up at 25C ambient. Temperature coefficients apply between
0C and 55C ambient.
Getting Started with the Model 433
1.
Excitation Supply. If remote sensing is not used, connect
+Sense to +Excitation, terminal 3 to 4, and connect
-Sense to -Excitation, terminal 1 to 2.
2.
Apply power to the Model 433 and adjust the Excitation
supply. Turn SWB-1 "ON" for a fixed 10 Volts. This will set
the supply to 10.2 2.5% and provide the best temperature
stability. For voltages between 5 and 10 Volts, place
SWB-1 in the "OFF" position and set the Excitation
Supply with potentiometer E. SWB-2 may be in either
position.
3.
Turn the power to the Model 433 off and connect the load
cell to the Model 433 Excitation terminals and the Amplifier
Inputs.
4.
Turn on power to the 433.
5.
Turn SWA-3 "ON". (To set output ZERO current with pot
D.)
6.
Select the expected full scale signal range according to
the table with SWA-4 and SWA-5. If the output from the
load cell is not known, set both SW-4 and SW-5 "ON" for
the 40-50mV range.
7.
Set SWA-2 "OFF" for 4mA or SWA-2 "ON" for 0mA output
ZERO.
8.
Adjust D potentiometer for desired ZERO current.
9.
Turn SWA-3 "OFF". Expect output current to change.
10. Apply no load or dead weight to load cell.
11. Adjust TARE potentiometers A and B for the same ZERO
current set in Step 8. SWA-1 "OFF" provides a bridge
output balance of -3mV to +15mV, and "ON" between
+15mV and +25mV.
12. Apply full scale load and adjust SPAN (GAIN)
potentiometer C for the desired full scale output current.
Set Range switches SWA-4 and SWA-5 as required.
13. Remove full scale load and check ZERO output current.
Adjust FINE TARE potentiometer A if required.
14. Recheck full scale as in Step 12.
15. End.
Note: If the amplifier is used without using the 433 Excitation
Supply, the external power supply low side must be
connected to the -EXCITATION terminal 2 on the
Model 433, or one of the inputs must be tied to
terminal 2, -EXCITATION. This provides a DC return
path for the finite amplifier input current.
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Amplifier
The amplifier is a true differential input, low drift Instrumentation
Amplifier with less than 100pA input current. It has a common
mode range of 5 Volts with respect to the - EXCITATION
supply terminal and a minimum of 100dB rejection of the
A
2401 Stanwell Drive Concord, California 94520 Ph: 925/687-4411 or 800/542-3355 Fax: 925/687-3333 www.calex.com Email: sales@calex.com
3
eco# 040325-2, 4/2001
Model 433 Bridgesensor
1
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Mechanical Specifications
SWA - Control Switch
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common mode voltage. The input amplifier and excitation
supply are DC isolated from the AC line and the current output.
The isolated output current source has a compliance of 20
Volts to allow the Model 433 to operate with zero to 1000
Ohms of loop resistance.
Tare Weight Compensation
The Model 433 has two different zero controls. One is called
the OUTPUT zero and can be set to 0mA or 4mA with SWA-
2. The other zero control is called TARE. SWA-1 allows the
selection of one of two TARE ranges, -3mV to 15mV or +15mV
to +25mV. Potentiometers are available for COARSE and
FINE TARE adjustments.
Connecting to a Sensor
Any amplifier has a finite input current which must have DC
return path to the amplifier power supplies. This path is
automatically provided when the Model 433 Bridge Excitation
Supply is used to excite the sensor. If an external supply is
used, one side of the external supply must be connected to the
Model 433 common, Terminal 2. Be sure that the common
mode voltage limits are observed. This would generally limit
the external power supply to 10 Volts assuming that half the
voltage would be common mode, as is the case when exciting
a full bridge.
When the full scale output of a sensor is measured in millivolts,
say 10 millivolts, care must be exercised in wiring systems. At
10 millivolts full scale, each microvolt (10
-6
volts) contributes
0.01% of full scale output. Wire connections can generate
microvolts of potential due to contact potentials. These will
also be thermoelectric potentials and thus vary with
temperature differences. All wires used in connecting up the
Model 433 should be of the same material. If any intervening
connections are made such as a terminal block, the terminal
block connecting points should have good thermal contact so
they will always be at the same temperature and thus cancel
each other.
Transducer Excitation
The bridge excitation supply voltage is set by SWB-1 and
potentiometer E. Set SWB-1 ON for a fixed 10 Volts. This will
provide the best temperature stability. The supply can be
adjusted between 5 and 10 Volts by setting SWB-1 OFF and
adjusting potentiometer E. The supply will deliver up to
120mA current at any voltage setting to power up to four 350
ohm sensors.
SWB - Excitation Voltage
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