DISPLACEMENT AND PERFORMANCE RATING
Loading error appears to be high for low values of the RL/RC ratio. Good accuracy is possible for RL/RC> 10, particularly for small values of q/qmax. It should be clear that the following actions can be taken to reduce loading error in pots:
1. Increase RL/RC (increase load impedance, reduce coil impedance).
2. Use pots only to measure small values of q/qmax (or calibrate only a small segment of the element for linear reading).
The loading-nonlinearity error is defined by
The error at q/qmax=0.5 is Note that this error is always negative. Using only a segment of the resistance element as the range of the potentiometer, is similar
A cable extension mechanism may be employed to accomplish this. A light cable wrapped around a spool, which moves with the rotary element of the transducer, is the cable extension mechanism.
The free end of the cable is attached to the moving object, and the potentiometer housing is mounted on a stationary structure. The device is properly calibrated so that as the object moves the rotation= count and fractional rotation measure will directly provide the rectilinear displacement.
A spring-loaded recoil device, such as a spring motor, will wind the cable back when the object moves toward\ the transducer.