Loss of optical input circuit

Claim 1

A loss of optical signal detector used with a signal generating circuit to detect the loss of an optical input signal, said signal generating circuit arranged to develop a signal voltage when said optical input drops below a preset threshold, said loss of optical signal detector comprising: signal coupling means including a first transistor having its base lead connected to said signal voltage from said signal generating circuit and its collector connected to a source of voltage and current and responsive to the application of said signal voltage from said signal generating circuit said first transistor turns on connecting said source of voltage and current to said first transistor emitter lead; signal voltage means including first and second resistors connected to said first transistor emitter lead, said signal voltage means arranged to receive said voltage and current from said signal coupling means and produce an output signal representing the loss of the optical signal; comparator means having a second transistor connected to said signal voltage means and a third transistor connected to said second transistor and to a reference voltage, said third transistor producing an alarm voltage in response to the application of said output signal from said signal voltage means to said second transistor when said signal voltage means output signal is greater than said reference voltage; and, alarm signal generating means connected to said comparator means third transistor, said alarm signal generating means receiving said alarm voltage and producing and sending an alarm signal to a controller interface indicating the loss of said optical input signal.