Traffic signal loop monitoring system
First Claim
1. A monitoring system for detecting a failure condition in an electrical network, said network including an inductive loop, a loop oscillator and a lead-in circuit connecting the inductive loop to the oscillator to cause the oscillator to generate a loop signal having a frequency (fL) determined by the inductance of the loop and lead-in circuit, said monitoring system including:
- control circuit means connected to said loop oscillator and including a reference source and comparator means coupled to the reference source and to the output of the loop oscillator and responsive to the loop signal for producing an output signal having a first value in the presence of said loop signal and a second value in th absence of said loop signal.
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Abstract
A monitoring system is provided for use in conjunction with a wire loop which is embedded in a roadway, and which senses the presence of vehicles in the roadway to control a traffic signal. The monitoring system senses the output of the loop oscillator which is included in the traffic control circuitry and which generates a loop signal and whose frequency-determining circuit includes the wire loop to indicate immediately any failure in the loop circuit. If for any reason the loop oscillator fails to operate, that fact will be sensed immediately by the monitoring system of the invention, and such a failure will be equated to a failure in the embedded loop, or in the lead-in circuit which connects the loop to the loop oscillator. A digital embodiment of the monitoring system of the invention includes a reference oscillator which generates a reference signal whose frequency is lower than the frequency of the loop signal, and it also includes a two-count binary counter which is clocked by the reference signal, and which is cleared by the loop signal so that the counter cannot exceed a count of one, so long as the loop oscillator is functioning. However, should the loop oscillator fail, indicating a failure condition in the loop, the counter will then proceed to the count of two, and that count will set a flip-flop to activate an appropriate indicator. The flip-flop will remain set and the indicator activated, until reset by appropriate manual means. An analog embodiment of the monitoring system of the invention is also provided.
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Citations
12 Claims
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1. A monitoring system for detecting a failure condition in an electrical network, said network including an inductive loop, a loop oscillator and a lead-in circuit connecting the inductive loop to the oscillator to cause the oscillator to generate a loop signal having a frequency (fL) determined by the inductance of the loop and lead-in circuit, said monitoring system including:
- control circuit means connected to said loop oscillator and including a reference source and comparator means coupled to the reference source and to the output of the loop oscillator and responsive to the loop signal for producing an output signal having a first value in the presence of said loop signal and a second value in th absence of said loop signal.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
Specification