Campbell Scientific 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules - Manual (Page 26)

4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bridge Terminal Input Modules (TIM)
The 4WFBS modules can support quarter bridge strain circuits using either the
completion resistor built into the TIM, or a user supplied “dummy” strain
gauge, for the Wheatstone Bridge arm's resistive element opposite of the active
strain gauge in the bridge. Wiring circuits using a dummy gage are covered in
Section 4.3.1.
4.3.1 Quarter Bridge Strain with Dummy Gauge Wiring Setup
Figure 4.3-2 illustrates the wiring of the strain gage with a dummy gage to the
4WFBS module, as well as the wiring of the module to the datalogger. This
shows the dummy gauge out at the remote site along with the active gage. This
is the best setup to achieve the best compensation for the apparent strain and
gauge factor variance due to temperature fluctuations, as it will be easier to
keep the temperature of the two gages equivalent.
FIGURE 4.3-2. ¼ bridge strain with remote dummy gauge
Figure 4.3-3 illustrates the wiring of the strain gage to the 4WFBS module with
the Dummy gauge at the logger location. Apparent strain errors could result
because of temperature variances between the two gauges with this setup. This
circuit is still utilized in some applications for ease of Shunt calibration (can
shunt across Dummy gage at logger location rather than at the remote gauge
location). Also an existing, standard 3-wire ¼ Bridge strain circuit can easily
be transformed into this circuit. If large temperature variances will exist
between the active gage and the dummy gage located at the datalogger, using
the 4WFBS completion resistor can result in lower temperature induced errors.
FIGURE 4.3-3. ¼ bridge strain with dummy gauge at datalogger
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