Abstract: A speed measurement system including a magnetic pickup positioned in proximate relation to a driven element of a gas turbine engine having a plurality of discontinuities therein. The pickup providing a pulse per every discontinuity and thus a multiplicity of pulses for every revolution of the driven element. Conditioning circuitry connected to the pickup for generating a strobe pulse signal for every discontinuity. Interval measuring circuitry receiving interval signals asynchronous to the strobe pulses of a predetermined period which are to form a measurement period which is exactly related to a count of the strobe pulses over a measurement period. Additionally included is circuitry used to lengthen the measurement period up to a maximum of N intervals for increasing the low frequency response of the system.

Abstract: A digital resolver processor measures the angle of a rotatable device. A resolver connected to the rotatable device generates sinusoidal signals as a function of an excitation signal and of the resolver angle. A phase shift network receives the sinusoidal signals and generates leading and lagging phase shifted signals with a relative phase shift proportional to resolver angle. A counter is enabled by the leading signal and inhibited by the lagging signal so that the contents of the counter represents the relative phase shift, and thus, the angle of the rotatable device. The angular position of the resolver is limited so that the contents of the counter is maintained within a predetermined range in the absence of a fault condition of the resolver terminals. The contents of the counter is forced outside the predetermined range in response to short or open circuit conditions of the resolver terminals, so that misleading angle representations may be recognized as such.