System for monitoring a periodic function

Abstract

A system for monitoring the frequency of a periodic function and indicating whether or not said function frequency differs from a predetermined frequency, with the function frequency being represented by an electrical signal having a parameter which varies systematically in accordance with the period of the function. A ramp signal generator is provided for generating a control signal having a characteristic which starts at a reference level and attains a predetermined level after the passage of a preselected period of time. A first switch is coupled to the control signal generating means and has two switching states with the switch being normally biased to one of its switching states but responsive to the control signal characteristic attaining the predetermined level for switching to the other of its switching states. An indicator is coupled to the first switch for indicating which state the switch is in. A second switch is coupled to the control signal generating means and is responsive to the systematic variation of the parameter for periodically re-setting the characteristic of the control signal to said reference level, whereby the first switch is in one of its two switching states when the function period is less than the preselected period of time and is in the other switching state when the function period is greater than the preselected period of time, and the system thus indicates whether or not the function is occurring at the predetermined frequency.

Dependencies are inferred from the claim text.