APPLICATION NOTE
3
Figure 4: Simulation result for Time-varying potentiometer circuit
The simulation results show the change in resistance as a function of time versus the output voltage to be
measured.
Modeling Variable Resistors: Strain Gauge Resistive
Bridge Circuit
Variable resistors can also be used to implement many kinds of sensors. For example, a strain gauge, which
consists of a resistance bridge, can be implemented using the following subcircuit:
.SUBCKT GAUGE (IN+ IN- OUT+ OUT-) PARAMS: R=1K F=0 SENS=1e-3
RUL IN+ OUT+ {R*(1+F*SENS)} ; upper left
RUR IN+ OUT- {R*(1-F*SENS)} ; upper right
RLL IN- OUT+ {R*(1-F*SENS)} ; lower left
RLR IN- OUT- {R*(1+F*SENS)} ; lower right
.ENDS
R can be determined by the gauge's current drain (I) at the bias voltage (V), that is, R = V/I. SENS sets the
sensitivity of the gauge and F is the applied force.
