Measurement Computing StrainBook/616 - Manual (Page 82)

6-18 Bridge Configurations 929494 StrainBook/616 User’s Manual
Caveats
Transducers and load cells, most often employ full bridges with four active strain gages to benefit from
inherent temperature compensation and maximum output signal levels.
The mV/V sensitivities vary from unit to unit, but series resistors may be placed in the excitation lines to
adjust them into a particular range window. This technique makes externally connected shunt calibration a
little less exacting if the shunt resistor is not connected directly across the desired bridge arm. A shunt
calibration resistor provided internally by the transducer manufacturer will usually require connection to an
externally accessible node to activate the shunt. The variations in connection requirements require the
flexibility of a non-committed dry contact as provided by the WBK16/LC module.
Shunt calibration generally is done by shunting one arm of a bridge with four active arms. For this reason,
it is recommended that simulated signal levels be limited to about 20% of the full-scale output of the
transducer. Attempting to achieve a high level output with a single resistor will introduce non-linearity
errors into the picture. For example, a 5000 pound load cell should be shunt calibrated with a resistance
that will introduce about a 1000 pound output signal. Attempting to produce a 4000 pound signal by
shunting one of the bridge legs will generally not produce the same quality result.