Capacitive displacement measuring instrument

摘要

A scale and slider in a linear displacement measuring instrument have spaced opposed parallel surfaces bearing aligned patterns of thin flat conductive elements. The scale pattern consists of equally spaced parallel bars transverse to displacement with enlarged aligned central portions which form collectively a single set of coupling electrodes. A pair of aligned sensor electrodes are fixed on the surface of the slider opposite the coupling electrodes of the scale and matching arrays of transmitter elements are arranged on opposite sides of the sensor electrodes and grouped axially in space quadrature. Alternate interdigitated sets of the transmitter electrodes on the slider are excited with oppositely phased square wave signals. The signals picked up by the sensor electrodes on the slider are fed to separate coarse plate counting and fine plate interpolation circuits. In the fine count circuit, the displacement-dependent amplitude of the signals from first one and then the other of the sensor electrodes is amplitude demodulated and digitally converted by a dual slope integrator. The reference signal for the return slope is furnished by placing cophase signals on the transmitter electrodes. Battery life is prolonged by staged power down modes which remove bias voltages from selected analog components while retaining limit values.