Quarter-Bridge Circuit (continued): Shunt Calibration

( ... continued )

Unless additional leadwires are used ( as demonstrated later ), simulating compressive strain by directly shunting the remote active gage is usually difficult to implement in practice. Since the purpose of shunt calibration in this case is simply to scale the instrument sensitivity as a means of compensating for leadwire resistance, either upscale or downscale calibration is equally suitable. Thus, it is generally more convenient to shunt the adjacent dummy arm as shown below, because this can be done right at the instrument terminals. It should be apparent from the figure that the calibration resistor must be connected directly across the dummy to produce the desired result.

Quarter-bridge circuit with active gage remote from instrument.

Gage strain cannot be accurately simulated by shunting from S- to P- (or from S- to P+). After shunting the dummy with a calibration resistor selected to simulate the appropriate strain, the instrument sensitivity is adjusted to register the same strain. At low strain levels, the result is effectively the same as if the calibration had been performed by shunting the active gage.

( continued... )

Page 14 of 50