Abstract: A capacitive strain gage includes a housing attachable to a test specimen at a first location and a ground plane attachable to the test specimen at a second location. The housing and the ground plane are movable relative to each other. A passage extends through the housing between opposing spaced-apart surfaces. First and second excitation electrodes are located on one of the surface, and a third signal electrode is located on the other of the surfaces. The electrodes each have fixed positions on the housing. Each of the first and second electrodes is positioned for capacitive coupling to the third electrode. The ground plane includes an arm that extends into the passage in the housing. The arm includes an aperture for electric fields that is aligned with the electrodes in a quiescent position.

Abstract: A signal conditioner for generation of excitation signals and for detecting an output signal from a capacitive transducer such as a strain gage, a pressure transducer or an accelerometer. The signal conditioner includes a digital waveform generator for generating a waveform that approximates a sine wave and for generating a binary signal synchronized to the waveform, a filter responsive to the waveform for providing a first sinusoidal excitation signal, an analog inverter responsive to the first excitation signal for providing a second sinusoidal excitation signal that is 180.degree. out of phase with the first excitation signal and a demodulator responsive to the binary signal for synchronously detecting an output signal from the capacitive transducer.