7
3.2
Transducer connections
Before connecting the transducer, check the excitation
voltage.
Applying an excitation voltage that is too high may
destroy the transducer
3.3
Full bridge Strain Gauge Transducer
Transducer connector details are as shown in Fig. 1 and on the S7DC circuit board.
To use the shunt calibration facility, insert a link between 'CAL' and 'SIG-'.
3.4
1/4 or 1/2 bridge transducer connections
For 1/4 bridge transducers, 3 bridge completion resistors are required. The active gauge
should be fitted on arm 'C' and the bridge completion resistors in arms D, A & B.
For 1/2 bridge systems, the active gauges should be C and D, and 2 completion resistors
are required.
The bridge completion resistors should be high stability, the same resistance as the active
gauge and may be fitted either in the transducer connector, or in the designated position on
the underside of the S7DC PCB. This requires removal of the PCB from the case.
R22 replaces bridge arm D, R23 replaces bridge arm A, R24 replaces bridge arm B
Note:
Mounting these resistors in the instrument is a compromise. To reduce temperature
and long lead effects, completion resistors should preferably be mounted at the
transducer and be of close tolerance and low t.c., e.g. 0.1%, 15 ppm..
3.5
Potentiometric Transducers
Select R24 value to drop at least 1.5V.
For example, with an excitation of say
10V and a potentiometer resistance of
500 ohms and R24 value of 100 Ohms,
the voltage drop across R24 = 10V /
(500+100) X 100 = 1.7V.
This raises terminal 4 to within the
common mode voltage range of the
amplifier.
Input signal = 10-1.7 = 8.3V so use the lowest gain range for ±10V output. For lower output
voltage or 4-20mA output, use lower excitation, e.g. 5V.
R24 can be added either in the solder pins on the underside of the PCB, or more easily into
the transducer screw terminals, between 'SIG-' and 'EXC-'
EXC-
A
B
C
D
EXC+
SIG+
SIG-
EXC+
SIG+
SIG-
EXC-
R24
POTENTIOMETER
