Cooper Instruments & Systems DCM 437 Current Bridge Amplifier - Manual (Page 4)

CF 27 4 4/2001
E. Determine the voltage of the power supply to be used and adjust within the 10 to 36 volt range if necessary
before connecting to the power pins, 1 and 2.
F. Verify that the hook up procedure is complete.
G. Turn on the power supply and check the bridge excitation supply.
II. Calibration Procedure
A. Set the GAIN SWITCH position 1 ON and all others OFF.
B. Short the signal input pins 9 and 10 together with a clip lead. Adjust the COARSE and FINE OFFSET pots,
C and B, for zero or 4 mA output current.
Note: Some PLC models do not accept negative inputs. The maximum negative current is 1 mA.
C. Remove the short between the signal input pins, 9 and 10. Adjust the BRIDGE BALANCE pot for zero or 4
mA output current.
D. Set the GAIN SWITCH to the expected load cell output.
E. Adjust the BRIDGE BALANCE pot for zero or 4 mA output current.
F. Apply the live load to the cell and adjust the GAIN, pot D, for the desired output current.
G. Remove live load and use the COARSE and FINE OFFSET pots to set the zero or 4 mA output current.
H. Repeat steps E. to G. until the desired settings are obtained.
Amplifier
The built-in amplifier is a true differential input, low noise, low drift, instrumentation amplifier. It has a high common
mode rejection ratio (CMRR) and is provided with an output offset that is potentiometer adjustable. The output
offset pots adjust the output zero current up to 12 mA. The zero current can also be adjusted for 0 to 20 mA output.
The instrumentation amplifier has a gain DIP switch which changes the gain by factors of two and a gain
potentiometer for fine adjustments.
The amplifier accepts input signals of 3 mV to 62 mV. The amplifier can withstand input voltages up to 15 Volts
without damage. The output of the amplifier is filtered to be 3 dB down at 10 Hz using a double pole Butterworth
filter to minimize the effects of high frequency electrical and physical noise on the system.
The DCM 437 has a Bridge Balance pot, which is connected internally to the amplifier - INPUT.
Transducer Excitation
Transducer excitation is provided by an adjustable, well-regulated, low noise power supply. The excitation voltage
is adjustable by means of a molded-in potentiometer, which allows the output voltage to be varied from 5 to 15
Volts. It is capable of supplying up to 150 mA to easily drive five 350-ohm load cells at 10 Volts.
The +Excitation supply has remote sensing provisions for 6 wire configurations. The sense lines minimize variations
in output voltage with changes in load current or lead resistance. The supply output, +Excitation, may be connected
through a 300-ohm safety barrier and the sense lines will regulate the voltage across a 350-ohm bridge between 5
and 8 volts.
The supply has short circuit protection to protect it against short-term faults. The output recovers automatically from
short circuit conditions once the short is removed.