Error detecting circuit for a traffic control system

• US 4,135,145 A
• Filed: 09/07/1976
• Issued: 01/16/1979
• Est. Priority Date: 09/07/1976
• Status: Expired due to Term

• Current Assignee: Display Technologies, Inc. (Rhode Island)
• Original Assignee: Solid State Devices, Inc.
• Inventors: Eberle, Terrence F.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): Groody, James J.
• Application Number:
  US05/720,841
• Time in Patent Office: 861 Days
• Field of Search: 340/46, 340/41 R, 340/248 E, 340/251, 340/35, 340/641, 340/642, 315/129, 315/130, 315/136, 235/150, 235/24, 364/436
• US Class Current: 340/931
• CPC Class Codes: G08G 1/097 Supervising of traffic control systems, e.g. by giving an alarm if two crossing streets have green light simultaneously

Abstract

An error detecting circuit which senses the operating states of a plurality of traffic signal lights the energization of which is controlled by a single block of load switches and which circuit produces an error signal when certain predetermined relations exist for a predetermined period of time between the states of the lights, such as, if more than one traffic signal light of one traffic signal head is energized simultaneously or if none of the traffic signal lights of one traffic signal head is energized.

Claims

1. In a traffic control system having a traffic controller, a plurality of load switches connected to and controlled by command signals from the traffic controller, traffic signal lights having different functions, traffic signal lights of a given function controlling the flow of traffic on one street of a plurality of intersecting streets being energizable from a source of AC potential by an energization circuit which includes a load switch, the load switches controlling the traffic signal lights for controlling the flow of traffic on one street constituting a group, the improvements comprising:

(a) a plurality of AC-DC converter circuits, one for each load switch of a given group of load switches;

(b) circuit means for respectively coupling a different AC-DC converter circuit to each energization circuit, each AC-DC converter circuit producing a logic signal having one value when AC potential is applied to it and a second value when no AC potential is applied to it;

(c) a logic circuit to which the logic signals from the AC-DC converter circuits are applied, said logic circuit producing an error signal if two traffic signal lights of a given group having inconsistent functions are energized simultaneously, or if no traffic signal lights of a given group are energized simultaneously;

(d) a time delay circuit;

(e) optical coupling means for applying the error signal produced by the logic circuit to the time delay circuit, said time delay circuit, if the error signal is applied continuously to it for a predetermined period of time, producing an output signal;

(f) circuit means including a silicon controlled rectifier and a photo diode, the photo diode being connected to the anode circuit of the silicon controlled rectifier, the output of the time delay circuit being connected to the gate of the silicon controlled rectifier, said output of the time delay circuit triggering the silicon controlled rectifier into conduction and causing the photo diode to produce visible radiation;

(g) an initializing circuit connected to the anode circuit of the silicon controlled rectifier for maintaining the voltage applied to the anode of the silicon controlled rectifier substantially equal to that of its cathode for a predetermined period of time after power is applied to the traffic control system; and

(h) switch means connected to the anode circuit of the silicon controlled rectifier for maintaining the voltage applied to the anode of the silicon controlled rectifier substantially equal to that of its cathode when the switch means is closed.

2. In the traffic control system of claim 1 in which the optical coupling means includes a photo diode and a photo transistor.

3. In the traffic control system of claim 1 in which the switch means is manually operated.

4. In a traffic control system of the type wherein there is provided a traffic controller for producing command signals, a plurality of load switches responsive to said command signals, and a plurality of traffic signal lights each coupled to one of said load switches, the improvements comprising:

a. first means coupled to each of said load switches for indicating when each of said load switches is energized;

b. second means for detecting when more than one load switch controlling a single phase of traffic is simultaneously energized or when no load switches controlling a single phase of traffic are energized and for producing an error signal in response thereto;

c. a time delay circuit coupled to said second means for receiving said error signal and producing an output signal when said error signal has been applied thereto for more than a predetermined period of time;

d. a latch circuit coupled to the output of said delay circuit and responsive thereto for producing a fault signal; and

e. third means coupled to said latch circuit for producing a visual signal in response to said fault signal.

5. The traffic control system of claim 4 wherein said first means comprises an AC-DC signal converter circuit.

6. The traffic control system of claim 5 further comprising a light emitting diode and a photo transistor for applying said error signal to said delay circuit.

7. The traffic control system of claim 6 wherein said third means is a light emitting diode.

8. An error detecting circuit for a single phase of traffic control system of the type wherein there is provided a traffic controller, a plurality of load switches coupled to and controlled by said traffic controller, said load switches arranged to control single phase traffic, a plurality of traffic signal lights each one of which is turned on and off by an energization circuit coupled between one of said load switches and said light;

said error detecting circuit comprising;

a. first means coupled to each of said load switches for producing signals indicative of the states of each of said load switches;

b. a logic circuit coupled to said first means and responsive to said signals for detecting when more than one of said load switches controlling said single phase is energized and for producing an error signal in response thereto;

c. a time delay circuit responsive to said error signal for producing an output signal if said error signal is applied thereto continuously for more than a predetermined period of time;

d. a latch circuit coupled to said delay circuit for producing a fault signal when said latch switches from a first to a second state in response to said output signal; and

e. third means coupled to said latch circuit for producing a visual signal when said latch circuit is in its second state.

9. The error detecting circuit of claim 8 wherein said first means comprises an AC-DC signal converter circuit.

10. The error detecting circuit of claim 9 further comprising a light emitting diode and a photo transistor for coupling said error signal to said delay circuit.

11. The error detecting circuit of claim 10 wherein said third means for producing a visual signal is a light emitting diode.

12. An error detector for use in a single phase of a traffic control system of the type wherein a plurality of traffic signal lights are selectively energized comprising, in combination:

a. first means for monitoring the states of each of said plurality of signal lights controlling said single phase of traffic; and

b. second means for detecting when at least two of said lights controlling said single phase are on or when none of said lights controlling said single phase are on and for generating an error signal in response thereto.

13. An error detector according to claim 12 wherein said first means for monitoring comprises:

a. third means for generating a plurality of signals, each one of said plurality of signals indicative of the condition of one of said traffic control lights.

14. An error detector according to claim 13 further including:

a. delay means having an input coupled to said second means for receiving said error signal; and

b. fourth means coupled to said delay means for triggering an alarm.

15. An error detector according to claim 14 wherein said third means includes a plurality of AC to DC converters, one for each of said plurality of traffic signal lights.

16. An error detector according to claim 15 wherein said alarm is a visual alarm.

17. An error detector according to claim 16 wherein said second means comprises logic means having inputs coupled to said plurality of signals and producing said error signal at its output.