Use of strain gauge for measuring voltage

The force of attraction between the capacitor plates is used to measure voltage by making one of the plates deflectable under the force of attraction. A strain gauge mounted on this plate suffers a shear strain which is detected electrically by the conventional technique of the Wheatstone bridge followed by an amplifier. The output of the amplifier was found to be linearly related to the square of applied voltage between the plates, as it theoretically should be. The technique can be used to measure dc and ac voltages, particularly when their magnitudes are high and there is also high impedance.