Position sensing control of the displacement of a first member relative to a second member particularly in a vehicular environment is aided by having a ratiometric relationship between the voltage supply for the sensor and the measuringcontrol portion of the apparatus. The errors are reduced based on variations between interferometry data acquired using the low coherence imaging interferometry system for a calibration sample and model interferometry data corresponding to data acquired for the calibration sample using a model interferometry system. A conductive layer disposed on the opaque layer. Any number of malfunctions can be detected including the presence of occlusions andor leaks.