the drive voltage and also to c 1 c 2 c 1 c 2 when synchronous detection is employed over the range from y gt d to y lt d reasonable linearity results if the electrodes of 6 are thin the planar shape is maintained and r gt gt d the equivalent circuit of the transducer in fig6 b is a symmetric bridge as before it is identical with fig2 except that c 1 c 2 c 3 and c 4 now assume the following values for the idealized unit equ1 to understand the indicated values of capacitance it is only necessary to recognize that the capacitance between parallel conducting plates of fixed common area is inversely proportional to the separation distance between the plates in the absence of fringe fields substituting these values into c 1 c 2 c 1 c 2 yields the output for this transducer example performance results for a prototype built in accord with fig6 a and b are provided in fig7 this data was obtained using a crudely constructed unit concerned primarily with detectability limits and not range or linearity large scatter is present primarily because of poor mechanical integrity in the u tube manometer used for pressure calibration the working fluid for the manometer was denatured alcohol specific gravity 0 7 which communicated with the sensor membrane 6 through an air column small bore tygon.