AU2006207867B2 - Power shutdown system for a traffic signal controller - Google Patents

Description

Regulation 3.2 Revised 2/98 AUSTRALIA Patents Act, 1990 ORIGINAL COMPLETE SPECIFICATION TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: Aldridge Traffic Systems Pty Limited ACTUAL INVENTOR: Andrew Bull ADDRESS FOR SERVICE: Peter Maxwell and Associates Level 6 60 Pitt Street SYDNEY NSW 2000 INVENTION TITLE: POWER SHUTDOWN SYSTEM FOR A TRAFFIC SIGNAL CONTROLLER DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO(S): 2005 904 889 - 6 September 2005 Australia The following statement is a full description of this invention including the best method of performing it known to us: m:\docs\20061041\1 05974.doc 2 The present invention relates to a power shutdown system for a traffic controller, as well as to a traffic controller that includes such a system. The present invention also relates to a testing arrangement for a power shutdown system for a traffic controller. 5 Although the discussion of the background to the invention that follows concerns electromechanical relays used in traffic control equipment, it is to be understood that the invention is not limited thereto, but has wider application to all kinds of power switching means, not just electromechanical relays, used in traffic control equipment to remove power from at least parts thereof. 10 In the prior art of controlling traffic lights by electronic and processor devices, it is generally considered necessary to arrange for the safe operation of the traffic control equipment even when some parts of the equipment have suffered some failure. As part of this process it is common to have an electromechanical relay whose function is to remove power from much of the 15 traffic control equipment so as to prevent the equipment from showing dangerous or conflicting signals when some faults are present in the equipment. In the field of machine safety, for example, a safety relay is often used to stop the operation of potentially hazardous machinery should some failures occur. In the normal course of use of machinery, the safety relay can 20 be tested periodically, for example, when the machinery is turned off at the end of a production cycle or work shift. In the field of traffic control, a relay is used for a similar purpose. However, as there is no normal "down time" when the operation of the relay can be tested without causing loss of power to the traffic lights, the relay remains untested for indefinitely long periods of time. It would 25 be advantageous, therefore, to allow the relay to be tested without removing power from the traffic lights. nr.nQ/ni 3 To ensure greater public safety, the reliability of traffic control equipment and its associated fault recovery equipment needs to be improved. To this end, it is common to consider improvements in the reliability of all parts of the equipment, but especially parts concerned with fault detection and 5 fault mitigation. It is an object of embodiments of the present invention to provide a power shutdown system for improving the safety of an intersection at which a traffic controller operates by means of electromechanical relays or the like power switching means to remove power from a faulty part of the traffic controller. 10 According to an aspect of the present invention, there is provided a power shutdown system for a traffic controller, the system including first and second power switching means having respective controllable current paths connected in parallel so that the first power switching means can maintain operation of the traffic controller when the second power switching means is being tested for a is fault in its operation. Preferably, the first and second power switching means comprise respective first and second electromechanical relays. Alternatively, the first and second power switching means comprise respective first and second sold state switches. 20 According to another aspect of the invention, there is provided a current based testing arrangement for the power shutdown system described above, comprising: (a) a control means adapted to periodically trigger a released state of a selected power switching means, and, 4 (b) a current measurement means for measuring current through the selected power switching means, whereby the measurement of a drop in current to zero through the selected power switching means when it is in its released state is indicative of normal 5 operation of the selected power switching means to assume the released state. According to yet another aspect of the invention, there is provided a voltage based testing arrangement for the power shutdown system described above, comprising: (a) a control means adapted to periodically trigger a released state of 10 the first or second power switching means, (b) third power switching means in series with the first power switching means, (c) fourth power switching means in series with the second power switching means, 15 (d) the control means being further adapted to trigger a released state of the fourth power switching means when the first power switching means is in its released state, and to trigger a released state of the third power switching means when the second power switching means is in its released state, and, 20 (e) a voltage measurement means for measuring voltage through the first or second power switching means, whereby the measurement of a drop in voltage to zero through the first or second power switching means when in its released state is indicative of normal operation of the first or second power switching means to assume the released 25 state.

4a In another broad form of the invention, there is provided a traffic controller comprising traffic signal control means and the power shutdown system described above. It is an object of the present invention to overcome or ameliorate at least 5 one of the disadvantages of the prior art, or to provide a useful alternative. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". 10 5 In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which: Fig. 1 is a circuit diagram of a current based testing arrangement for a 5 power shutdown system for a traffic controller, in accordance with a preferred embodiment of the invention, and Fig. 2 is a circuit diagram of a voltage based testing arrangement for a power shutdown system for a traffic controller, in accordance with another preferred embodiment of the invention. 10 As shown in the drawings, the single electromechanical relay of the prior art is replaced by two or more electromechanical relays connected with their contact sets in parallel so that either relay can maintain normal or uninterrupted operation of the traffic control equipment when the other relay is being tested. Although the parallel connection of the contact sets of the relays results 15 in a small reduction in reliability of the power shutdown system (also known in the art as a disconnect mechanism), this is more than compensated for by a much larger improvement in reliability as a result of being able to test the electromechanical relays more regularly. This reduction in the mission time (or time following a successful test) for the relays increases the probability that 20 the relays will operate normally at any point in time. In the description that follows of the features shown in the drawings, it will be understood that the electromechanical relays could be replaced with other power switching means, such as solid state switches, without changing the essential nature of the invention. 25 With reference to the embodiment shown in Fig. 1, current measurement is used to test the power shutdown system for the traffic controller. The testing arrangement utilizes current transformers 12, 14, but other current no/Anq/nA 6 measurement devices, such as hall effect devices or current sense resistors, may alternatively be used. The testing of the relays 16 and 18 is performed by use of control unit 20. Control unit 20 periodically releases relay 16 and confirms the proper 5 operation of the release function by measuring the current through contact 22 of relay 16 using current transformer 12 and recognizing that the current has dropped to zero while the current through the contact 24 of relay 18 as measured using current transformer 14 is not zero and relay 18 supplies power to the traffic lanterns. By a similar procedure, the proper operation of relay 18 10 can also be checked periodically. With reference to the embodiment shown in Fig. 2, voltage measurement is used to test the power shutdown system for the traffic controller. The control unit 30 can measure the voltage on nodes 32 and 34. The 15 testing of the relays 36 and 38 is performed by use of control unit 30. Control unit 30 periodically releases relay 36 and confirms the proper operation of the release function by releasing relay 40 and confirming that the voltage on node 32 falls to zero. This operation also checks the release operation of relay 42. By a similar procedure, the proper operation of relay 38 and relay 40 can be 20 checked. By the use of these arrangements, the mission time of the relays can be reduced to any selected time without having to remove power to the traffic lanterns. It will be apparent to persons skilled in the art that various modifications 25 may be made in details of design and construction of the power shutdown system described above without departing from the scope and ambit of the invention. nnIna/nr

Claims (8)

1. A current based testing arrangement for a power shutdown system for a traffic controller, the system including first and second power switching means having respective controllable current paths connected in parallel so that the first 5 power switching means can maintain operation of the traffic controller when the second power switching means is being tested for a fault in its operation, the arrangement comprising: (a) a control means adapted to periodically trigger a released state of a selected power switching means, and, 10 (b) a current measurement means for measuring current through the selected power switching means, whereby the measurement of a drop in current to zero through the selected power switching means when it is in its released state is indicative of normal operation of the selected power switching means to assume the released state. 15

2. The current based testing arrangement of claim 1 wherein the first and second power switching means comprise respective first and second electromechanical relays.

3. The current based testing arrangement of claim 1 wherein the first and second power switching means comprise respective first and second solid state 20 switches.

4. A voltage based testing arrangement for a power shutdown system for a traffic controller, the system including first and second power switching means having respective controllable current paths connected in parallel so that the first power switching means can maintain operation of the traffic controller when the 8 second power switching means is being tested for a fault in its operation, the arrangement comprising: (a) a control means adapted to periodically trigger a released state of the first or second power switching means, 5 (b) third power switching means in series with the first power switching means, (c) fourth power switching means in series with the second power switching means, (d) the control means being further adapted to trigger a released state 10 of the fourth power switching means when the first power switching means is in its released state, and to trigger a released state of the third power switching means when the second power switching means is in its released state, and, (e) a voltage measurement means for measuring voltage through the 15 first or second power switching means, whereby the measurement of a drop in voltage to zero through the first or second power switching means when in its released state is indicative of normal operation of the first or second power switching means to assume the released state. 20

5. The voltage based testing arrangement of claim 4 wherein the first and second power switching means comprise respective first and second electromechanical relays. 9

6. The voltage based testing arrangement of claim 4 wherein the first and second power switching means comprise respective first and second solid state switches.

7. A current based testing arrangement for a power shutdown system for a 5 traffic controller substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.

8. A voltage based testing arrangement for a power shutdown system for a traffic controller substantially as herein described with reference to any one of io the embodiments of the invention illustrated in the accompanying drawings and/or examples.