Abstract: A non-contacting potentiometer includes a resistor and a movable probe which capacitively couples AC signals applied to the resistor to an output terminal. A closed loop control circuit is coupled to the resistor and the probe to compensate for variations in gap spacing between the probe and resistor.

Abstract: An interval timer circuit includes an RC circuit selectively coupled to a reference voltage source such that when power is removed, the capacitor discharges in a predictable manner to provide a time dependent but power supply independent voltage across the capacitor which can be employed to determine the downtime of electrical equipment or machinery.

Abstract: An A/D converter includes a limiting circuit for limiting the amplitude of bipolar input signals. A comparator compares the amplitude limited signals with reference voltages and provides pulse output signals corresponding to the duration of each half-cycle of the bipolar signals. The pulse output signals are applied to a counter circuit which counts clock pulses for each of the half-cycle intervals to provide a digital word for each half-cycle of bipolar signal information which accurately indicates the duration of each half-cycle of the input signal. The A/D circuit is employed, in one embodiment of the present invention, with a microprocessor programmed to analyze the engine speed signals from a tachometer according to a prescribed relationship to provide output information useful for predicting when engine maintenance is required.