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Strain Gage Connections and Bridge Circuits

Since the resistance change of a strain gage is very small, it requires the
use of a Wheatstone bridge circuit. The simplest method is to place a strain
gage into one arm of the bridge circuit, while placing fixed resistors into
the remaining three arms. This configuration is called a Quarter bridge.
Using a 3-wire lead wire to connect the strain gage to the strain
instrumentation will cancel any change in resistance in the lead wire due to
a change in temperature. This is called a Quarter bridge 3-wire system.
Placing strain gages in two of the bridge arms results in a Half bridge.
This method has the advantage of either doubling the output voltage, or
compensating for thermal outputs of the gages, depending on the strain gage
application. In a Full bridge connection, all four arms are replaced by
strain gages, yielding re-doubled output and compensation of temperature
effects. TML strain meters have functions for arranging the bridge circuits,
applying excitation voltage and amplifying and reading the resulting output
voltages. Bridge circuits can be completed by connecting the strain gages
and setting the instrument switches according to the desired configuration
for each strain meter.