3. Variable electrical impedance sensors

To avoid redundancy, the principle and advantages of the push-pull system are presented here in a general context. Its use will be mentioned later, whenever necessary. The purpose of this type of structure, whose implementation depends on the sensor's operating principle (it's not applicable in all cases), is to double measurand sensitivity and compensate for even-order non-linearities. The term compensate is here opposed in meaning to the term correct in that compensation is intrinsic and structural (two opposing physical effects compensate) and correction is corollary (a signal is corrected after it has been created, on the basis of data from another measurement).

The structure of a push-pull circuit assumes that the measurand is small compared with one of the sensor's constituent quantities. In the case of displacement measurement, for example, the position variation...