A fault detection system including first and second transducers adapted to receive alternating current, a common conductor coupled to the transducers, and a failure detector. The alternating current from the transducers is substantially oppositely phased so that, under normal operating conditions, the current level on common conductor is relatively low. When a failure in one of the transducers occurs, the current level on the common conductor increases at least to a predetermined level. The failure detector is responsive to the current level on the common conductor rising to such predetermined level to provide a failure signal.
An alarm system which includes at least one primary detecting device that provides an analog output signal. The rate of change of the analog output signal is monitored, and an alarm signal is generated when the rate of change exceeds a preset limit. The analog output signal is also compared with a first reference level signal to provide a pre-maintenance warning signal when the analog output signal reaches the first reference level.
A method and system for detecting faults with a self-exciting sensor includes a monitor circuit coupled to the self-exciting sensor for monitoring a signal associated with the sensor and generating a failure signal. A voltage limiting circuit is coupled to a receiver circuit associated with the self-exciting sensor for generating a first output signal within a valid range of operation in the absence of the failure signal. The voltage limiting circuit also generates a second output signal outside the valid range of operation in response to the failure signal so as to eliminate the necessity of an additional input to control logic associated with the self-exciting sensor.
