Circuit for monitoring the operating condition of an electric load

Claim 1

Apparatus for monitoring the operating condition of a valve heater connected across a power source by power lines so as to normally draw current, comprising: first integrated circuit timer means including a timer output terminal and a voltage sensing terminal, said timer means being operative to provide a first signal on its timer output terminal when the voltage on said voltage sensing terminal is above a first threshold and to provide a second signal on its timer output terminal when the voltage on said voltage sensing terminal is below a second threshold, lower than said first threshold; a current sensor connected in said power line between said power source and said valve heater, said current sensor having an output connected to said voltage sensing terminal of said first timer means and providing an output voltage which is above said first threshold when current is flowing between said power source and said valve heater and which is below said second threshold when no current is flowing between said power source and said valve heater, whereby the output signal of said first timer means indicates whether said valve heater is drawing current; first indicator means connected to said timer output terminal of said first timer means, said indicator means including a lamp which becomes illuminated when said timer is providing said first signal, and which is not illuminated otherwise, thereby providing a visual indication when current is flowing to said valve heater; second integrated circuit timer means including a timer output terminal and a voltage sensing terminal, said voltage sensing terminal being connected to said timer output terminal of said first integrated circuit timer means, said second timer means providing a third signal on its timer output terminal when said first timer means is providing said first signal and providing a fourth signal on its timer output terminal when said first timer means is providing said second signal; and second indicator means connected to said timer output terminal of said second timer means, said second indicator means including a lamp which periodically illuminates in response to said fourth signal and is not illuminated otherwise, said second indicator means thereby providing a flashing visual indication whenever no current is flowing between said source and said valve heater.