Installation
2
0
1
8
-1
2
51
3.11
Strain Gage Measurement
I/O modules FB4*01* and FB5202* can be interconnected for strain gage measurements. Use
analog output FB4*01* to create a constant current, and the measuring input for temperature
input FB5202* to process the millivolt signal for the resulting bridge voltage.
A constant current of 20 mA is sufficient to power a 350-
Ω
bridge. A bridge voltage of 7 V is
produced. With a bridge sensitivity of 2 mV/V, a voltage of 14 mV results at full load.
Configuring I/O Modules for Strain Gage Measurement
1. Either set the FB4*01* analog output operating mode to
simulation
and select 20 mA as the
simulation value, or set a fixed value of 20 mA via the fieldbus.
2. Set the FB5202* temperature input to a millivolt measurement
mV
.
3. Deactivate the cold junction of temperature input FB5202* by setting the thermostat
temperature for the external cold junction to
0
°C
.
Figure 3.22
Example of a strain gauge bridge
Bus
5*02
4*01
+
–
2+
5 -
6 -
5+
+
–
