FAIL-SAFE WALK-DON'T WALK SIGNAL
United States Patent 3596238
Fail-safe electrical circuit arrangements are provided which are particularly useful in connection with Walk-Don't Walk pedestrian traffic control signals to prevent a Walk light from being actuated should the Don't light indication be defective. The circuit arrangements comprise first and second semiconductor bilateral switches, a gate circuit and a Don't and a Walk light. If voltage is applied to both lights and the Don't light does not operate, the switches prevent the illumination of the Walk light.
Application Number:
04/751130
Publication Date:
07/27/1971
Filing Date:
08/08/1968
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Export Citation:
Assignee:
The Marbelite Company, Inc. (Brooklyn, NY)
Primary Class:
Other Classes:
327/582, 315/119
International Classes:
G08G1/097; G08G1/097
Field of Search:
340/41,46,44 307/305,35K
Other References:
Electrical Design News, Vol. 9 -7 June 1964 Page 115 (copy in 340-46).
Primary Examiner:
Cooper, William C.
Claims:
What I claim is
1. A fail-safe electrical circuit arrangement comprising:
2. A fail-safe electrical circuit arrangement in accordance with claim 1 wherein said first and second signal lights each comprise at least one electric bulb.
3. A fail-safe electrical circuit arrangement in accordance with claim 1 wherein said source of alternating current is interconnected with the second terminal of said first bilateral switch,
4. A fail-safe electrical circuit arrangement in accordance with claim 1 wherein said second terminals of said first and second bilateral switches are interconnected with said source of alternating current,
5. A fail-safe circuit adapted for use in a traffic control system comprising:
6. A fail-safe circuit in accordance with claim 5 including a second resistive means interconnecting the first terminal and gate terminal of said second bilateral switch.
7. A fail-safe circuit adapted for use in a traffic control system comprising:
8. A fail-safe circuit adapted for use in a traffic control system coupled to a first signal light for displaying a proceed indication and a second signal light for indicating a stop condition comprising:
1. A fail-safe electrical circuit arrangement comprising:
2. A fail-safe electrical circuit arrangement in accordance with claim 1 wherein said first and second signal lights each comprise at least one electric bulb.
3. A fail-safe electrical circuit arrangement in accordance with claim 1 wherein said source of alternating current is interconnected with the second terminal of said first bilateral switch,
4. A fail-safe electrical circuit arrangement in accordance with claim 1 wherein said second terminals of said first and second bilateral switches are interconnected with said source of alternating current,
5. A fail-safe circuit adapted for use in a traffic control system comprising:
6. A fail-safe circuit in accordance with claim 5 including a second resistive means interconnecting the first terminal and gate terminal of said second bilateral switch.
7. A fail-safe circuit adapted for use in a traffic control system comprising:
8. A fail-safe circuit adapted for use in a traffic control system coupled to a first signal light for displaying a proceed indication and a second signal light for indicating a stop condition comprising:
Description:
BACKGROUND OF THE INVENTION
In recent years, Walk-Don't Walk pedestrian traffic control signals have come into increasing use particularly in large cities. Such devices are known to act as important safety signals and are often relied upon by pedestrians at crowded intersections. It is customary to employ a housing having an upper reflector and a lower reflector with the upper reflector being positioned in back of a stencilled Don't sign and the lower reflector being positioned in back of a stencilled Walk sign. Often a single bulb is mounted in the upper reflector and a plurality of bulbs are mounted in the lower reflector so that the Walk portion of the sign is actuated by a circuit through one bulb lying behind the Walk stencil and the Don't Walk signal is given by activating a bulb in the top reflector simultaneously with a bulb in the lower reflector. One such known pedestrian traffic control signal is described in U.S. Pat. No. 3,141,149.
Problems arise when one or more of the bulbs used to actuate the Don't Walk signal burn out as frequently happens. These bulbs are often connected in series. Thus, if the Walk bulb burns out, there is a safety problem since the Don't bulb will not light up. Moreover, a service problem results since both bulbs must be tested to determine which is defective.
An additional problem known in the art is that involved in the use of large step up transformers in order to convert a standard AC power supply for use with two standard 67- watt, 120- volt bulbs or lamps in series commonly employed in Walk-Don't Walk signals. Such transformers take up a considerable amount of space and are expensive. In addition, electrical contacts used in such systems are subject to short life because of the high inductive load. If 60- volt lamps are used, their cost is extremely high as compared to the use of standard 120 -volt traffic signal bulbs.
SUMMARY OF THE INVENTION
According to the present invention, fail-safe circuit arrangements are provided which are particularly adapted for use in connection with Walk-Don't Walk pedestrian control illuminated signals. First and second semiconductor bilateral switches are provided with gate circuit means interconnecting the first and second switches. A first electrical response means is in series with and forms a part of the gate circuit means. A second electrical response means is interconnected with at least one of the switches so that when an AC voltage is supplied to one of the switches, the first and second response means are activated if they permit current flow therethrough, and not activated if neither permits current flow therethrough as when both bulbs are burned out in a traffic control pedestrian signal. When the AC voltage is applied to one of the switches and the first response means which may correspond to the Don't bulb is burned out and does not permit current flow therethrough, the gate means prevents actuation of the second electrical response means which may correspond to the electric bulb normally lighting up the Walk portion of a pedestrian signal.
Preferably the first electrical response means can be activated even if the second electrical response means is defective and does not permit current flow therethrough. This is an important feature of the invention as applied to pedestrian traffic control signals. Thus, if the Walk bulb of the Don't Walk circuit is burned out, the Don't bulb will still be operative at the appropriate time to act as a safety signal while the Walk bulb will never light up if the Don't bulb is burned out.
The electrical circuit arrangement of this invention is relatively uncomplicated and provides for long life particularly in view of solid-state devices used. Moreover, 120 -volt standard traffic control lamps can be used and the necessity for conventional large sized expensive transformers in pedestrian traffic control signals can be avoided. Testing of the arrangements of this invention can be rapidly carried out with minimum effort.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages and features of the present invention will be better understood from the following specification when read in conjunction with the accompanying drawings in which:
FIG. 1 is a diagrammatic sketch of a preferred embodiment of the fail-safe electrical circuit arrangement of this invention with a pedestrian traffic control signal being diagrammatically represented;
FIG. 2 is a diagrammatic view of an alternate embodiment thereof;
FIG. 3 is a diagrammatic view of another alternate embodiment thereof; and,
FIG. 4 is a diagrammatic view of gate circuits in the circuit arrangement of FIG. 3.
DESCRIPTION OF PREFERRED EMBODIMENTS
With reference now to the drawings and more particularly FIG. 1, a first preferred embodiment of the invention is illustrated at 10 wherein the circuit arrangement comprises a pedestrian traffic control signal housing diagrammatically shown at 11, a Walk bulb 12 and a Don't bulb 13. Two conventional semiconductor bilateral switches TR1 and TR2 are provided interconnected in the circuit arrangement 10 as will be described.
Each of the semiconductor bilateral switches can be conventional gate controlled semiconductor switches as known in the art as for example TRIAK (a product of Radio Corporation of America, No. 40,526 ) 2 -amp switches each having pins 1, 2 and 3 corresponding to main terminal 1, main terminal 2 and gate terminal 3.
The pedestrian signal 11 preferably has 120 -volt lamps 12 and 13 each electrically connected to a ground 14 and 15 respectively as diagrammatically shown with a second line through their filaments interconnected with terminals 16 and 17. The signal 11 is of a conventional type as described in said above-noted patent where upper and lower reflectors contain Don't bulb 13 and Walk bulb 12 respectively with corresponding glass stencil fronts. A second Walk bulb is carried by the lower reflector. A conventional current supply is provided with timing means for alternately powering the Walk bulb and the Don't, Walk bulbs 12, 13.
A mechanical switch 18 is provided interconnected with an AC 120 -volt current supply through a controller as is well-known, and is interconnected with pin 2 of TR1. Pin 3 of TR1 is in series with pin 3 of TR2 and bulb 13 through an electrical connection between pin 2 of TR2 and terminal 17. Preferably a 10K resistor 19 is provided to protect the gates at pins 3 of TR1 and TR2. Pins 1 of TR1 and TR2 are electrically connected by wires 22 and 23 through terminal 16 to the Walk bulb 12 which is connected to the ground as indicated at 14.
From the above description, it will be understood that there is a gate circuit passing through on-off switch 18, pins 2 and 3 of TR1, pins 3 and 2 of TR2, bulb 13 to ground 15. If the Don't bulb 13 has a burned out filament, no current will pass through the Walk bulb 12 since the lack of an active gate circuit will prevent passage of current through both TR1 and TR2 in this case. Thus, neither semiconductor switch will turn on to permit passage of current to pin 1 of either unless the gate circuit passing through pins 3 of TR1 and TR2 is operative through the Don't bulb. On the other hand, even though the Walk bulb 12 may have a burned out filament, and be inoperative, if the Don't bulb is not defective, current can still pass through the gate circuits and the Don't bulb will be illuminated upon actuation by the AC power supply through mechanical switch 18, pins 2 to 1 of TR1 and pin 1 to 2 of TR2 to Don't lamp 13 and ground 15.
One advantage of the preferred embodiment described above is the ease of testing the device. Thus, if either TR1 or TR2 is removed from the circuit both lights will be turned off since neither TR1 nor TR2 will work without the other and either one can be tested by removing the other.
One hundred twenty-volt lamps or bulbs can be used with a standard 120 -volt AC power supply.
When both bulbs 12 and 13 are operative and have operative filaments, and the mechanical switch 18 is turned on, the gate circuit will be actuated first after which TR1 and TR2 will permit current flow between pins 2 and 1 so that the Walk light will actually turn on first although the speed of the entire circuit is so fast that the Don't light is actuated substantially simultaneously and a pedestrian will not be able to determine which light goes on first.
Turning now to the embodiment of FIG. 2, identical elements of the circuit arrangements 20 are numbered the same as corresponding elements in the embodiment of FIG. 1.
In embodiment 20, line 22 from pin 1 to line 23 interconnecting pin 1 of TR2 and bulb 12 is eliminated and pin 1 of TR1 is connected directly to Walk bulb 12 while pin 1 of TR2 is connected directly to Don't bulb 13. A resistor (preferably 10K resistor) 21 is provided between pins 1 and 3 of TR2 and switch 18 provides AC power to both pin 2 of TR1 and pin 2 of TR2. Resistor 19 in this embodiment is a 3.9K resistor. In this embodiment, TR1 does not carry the total current of both bulbs as is the case in the embodiment of FIG. 1. Moreover, if the Don't bulb is operative, it will be activated by AC current flow through TR2 even though the Walk bulb 12 may be inoperative due to the fact that passage of the current through the gate of TR2 is permitted since a gate current is established between switch 18, pins 2 and 3 of TR2, through 10K resistor 21 to pin 1 of TR2. If the Don't bulb 13 is burned out, TR2 can't turn on and pins 2 and 3 of TR2 have no voltage across them and no current flow is possible. Pins 3 and 2 of TR1 are at the same AC potential which keeps TR1 turned off in this case. When Don't bulb 13 is operative, there is a small voltage drop across TR2 so that TR1 will turn on. If the Walk light 12 is burned out, the Don't will still turn on since the Walk light is in parallel circuit arrangement to the Don't light and would not affect the working of the Don't light. This is so since there will still be a voltage difference between pins 2 and 3 of TR2 since the resistor 21 completes the gate circuit of TR2. In this embodiment, the gate circuits of TR1 and TR2 are in series with Don't bulb 13 but are not in series with each other as in the embodiment of FIG. 1. The circuit arrangement 20 accomplishes the same function as the circuit arrangement 10. Moreover, neither bilateral switch TR1 or TR2 carries the total current of both bulbs allowing the use of lower rated bilateral switch components.
Turning now to the embodiment of FIG. 3, an alternate circuit arrangement 30 is illustrated wherein corresponding parts of circuit arrangement 30 and circuit arrangements 10 and 20 are indicated by corresponding numbers.
In this embodiment, pin 1 of TR1 is grounded at 32, gate circuit resistor 19 is replaced by a resistor 31 connecting pin 3 of TR1 and pin 2 of TR2 and having a value of 2.6K. The lamp wiring in this embodiment is slightly more difficult than the embodiments of FIGS. 1 and 2 since one terminal of Walk bulb 12 is connected to AC positive while the other terminal is connected to pin 2 of TR1. AC positive current is supplied through switch 18 to pin 1 of TR2. The gate circuits of TR1 and TR2 are illustrated at FIG. 4 where the arrows represent current flow in the gate circuits of TR1 and TR2.
The Don't bulb 12 can be turned on if its filament is intact since there is a ground potential at pin 2 of TR2 which completes a gate circuit to pin 3 of TR2 through resistor 21 to pin 1 of TR2 which is at AC potential. In this case, a ground potential is applied to pin 2 of TR2 through resistor 31 to pin 3 of TR1 which completes a circuit between pins 1 and 2 of TR1 to bulb 12 thus turning on the Walk bulb 12. In this embodiment, each of the gate circuits of TR1 and TR2 are in series with the Don't bulb 13 but are not in series with each other. Thus, if the Don't bulb 13 is burned out, the Don't and Walk bulbs will be inoperative. If the Walk bulb is inoperative, the Don't bulb will still be actuated by the on-off switch 18. As in the embodiment of FIG. 2, the Don't bulb is in series with each of the gate circuits but the gate circuits are not in series with each other.
While specific embodiments of the present invention have been shown and described, it should be understood that many variations thereof are possible. For example, the specific values given for the solid-state switches, current supply and resistors can vary in different circuit arrangements. Other than standard 120- volt bulbs can be used. In some cases, the circuit arrangement can be used for response means other than bulbs such as bells, alarm signals, on-off control devices and the like.
In view of the many modifications possible, this invention is to be limited only by the spirit and scope of the appended claims.
In recent years, Walk-Don't Walk pedestrian traffic control signals have come into increasing use particularly in large cities. Such devices are known to act as important safety signals and are often relied upon by pedestrians at crowded intersections. It is customary to employ a housing having an upper reflector and a lower reflector with the upper reflector being positioned in back of a stencilled Don't sign and the lower reflector being positioned in back of a stencilled Walk sign. Often a single bulb is mounted in the upper reflector and a plurality of bulbs are mounted in the lower reflector so that the Walk portion of the sign is actuated by a circuit through one bulb lying behind the Walk stencil and the Don't Walk signal is given by activating a bulb in the top reflector simultaneously with a bulb in the lower reflector. One such known pedestrian traffic control signal is described in U.S. Pat. No. 3,141,149.
Problems arise when one or more of the bulbs used to actuate the Don't Walk signal burn out as frequently happens. These bulbs are often connected in series. Thus, if the Walk bulb burns out, there is a safety problem since the Don't bulb will not light up. Moreover, a service problem results since both bulbs must be tested to determine which is defective.
An additional problem known in the art is that involved in the use of large step up transformers in order to convert a standard AC power supply for use with two standard 67- watt, 120- volt bulbs or lamps in series commonly employed in Walk-Don't Walk signals. Such transformers take up a considerable amount of space and are expensive. In addition, electrical contacts used in such systems are subject to short life because of the high inductive load. If 60- volt lamps are used, their cost is extremely high as compared to the use of standard 120 -volt traffic signal bulbs.
SUMMARY OF THE INVENTION
According to the present invention, fail-safe circuit arrangements are provided which are particularly adapted for use in connection with Walk-Don't Walk pedestrian control illuminated signals. First and second semiconductor bilateral switches are provided with gate circuit means interconnecting the first and second switches. A first electrical response means is in series with and forms a part of the gate circuit means. A second electrical response means is interconnected with at least one of the switches so that when an AC voltage is supplied to one of the switches, the first and second response means are activated if they permit current flow therethrough, and not activated if neither permits current flow therethrough as when both bulbs are burned out in a traffic control pedestrian signal. When the AC voltage is applied to one of the switches and the first response means which may correspond to the Don't bulb is burned out and does not permit current flow therethrough, the gate means prevents actuation of the second electrical response means which may correspond to the electric bulb normally lighting up the Walk portion of a pedestrian signal.
Preferably the first electrical response means can be activated even if the second electrical response means is defective and does not permit current flow therethrough. This is an important feature of the invention as applied to pedestrian traffic control signals. Thus, if the Walk bulb of the Don't Walk circuit is burned out, the Don't bulb will still be operative at the appropriate time to act as a safety signal while the Walk bulb will never light up if the Don't bulb is burned out.
The electrical circuit arrangement of this invention is relatively uncomplicated and provides for long life particularly in view of solid-state devices used. Moreover, 120 -volt standard traffic control lamps can be used and the necessity for conventional large sized expensive transformers in pedestrian traffic control signals can be avoided. Testing of the arrangements of this invention can be rapidly carried out with minimum effort.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other advantages and features of the present invention will be better understood from the following specification when read in conjunction with the accompanying drawings in which:
FIG. 1 is a diagrammatic sketch of a preferred embodiment of the fail-safe electrical circuit arrangement of this invention with a pedestrian traffic control signal being diagrammatically represented;
FIG. 2 is a diagrammatic view of an alternate embodiment thereof;
FIG. 3 is a diagrammatic view of another alternate embodiment thereof; and,
FIG. 4 is a diagrammatic view of gate circuits in the circuit arrangement of FIG. 3.
DESCRIPTION OF PREFERRED EMBODIMENTS
With reference now to the drawings and more particularly FIG. 1, a first preferred embodiment of the invention is illustrated at 10 wherein the circuit arrangement comprises a pedestrian traffic control signal housing diagrammatically shown at 11, a Walk bulb 12 and a Don't bulb 13. Two conventional semiconductor bilateral switches TR1 and TR2 are provided interconnected in the circuit arrangement 10 as will be described.
Each of the semiconductor bilateral switches can be conventional gate controlled semiconductor switches as known in the art as for example TRIAK (a product of Radio Corporation of America, No. 40,526 ) 2 -amp switches each having pins 1, 2 and 3 corresponding to main terminal 1, main terminal 2 and gate terminal 3.
The pedestrian signal 11 preferably has 120 -volt lamps 12 and 13 each electrically connected to a ground 14 and 15 respectively as diagrammatically shown with a second line through their filaments interconnected with terminals 16 and 17. The signal 11 is of a conventional type as described in said above-noted patent where upper and lower reflectors contain Don't bulb 13 and Walk bulb 12 respectively with corresponding glass stencil fronts. A second Walk bulb is carried by the lower reflector. A conventional current supply is provided with timing means for alternately powering the Walk bulb and the Don't, Walk bulbs 12, 13.
A mechanical switch 18 is provided interconnected with an AC 120 -volt current supply through a controller as is well-known, and is interconnected with pin 2 of TR1. Pin 3 of TR1 is in series with pin 3 of TR2 and bulb 13 through an electrical connection between pin 2 of TR2 and terminal 17. Preferably a 10K resistor 19 is provided to protect the gates at pins 3 of TR1 and TR2. Pins 1 of TR1 and TR2 are electrically connected by wires 22 and 23 through terminal 16 to the Walk bulb 12 which is connected to the ground as indicated at 14.
From the above description, it will be understood that there is a gate circuit passing through on-off switch 18, pins 2 and 3 of TR1, pins 3 and 2 of TR2, bulb 13 to ground 15. If the Don't bulb 13 has a burned out filament, no current will pass through the Walk bulb 12 since the lack of an active gate circuit will prevent passage of current through both TR1 and TR2 in this case. Thus, neither semiconductor switch will turn on to permit passage of current to pin 1 of either unless the gate circuit passing through pins 3 of TR1 and TR2 is operative through the Don't bulb. On the other hand, even though the Walk bulb 12 may have a burned out filament, and be inoperative, if the Don't bulb is not defective, current can still pass through the gate circuits and the Don't bulb will be illuminated upon actuation by the AC power supply through mechanical switch 18, pins 2 to 1 of TR1 and pin 1 to 2 of TR2 to Don't lamp 13 and ground 15.
One advantage of the preferred embodiment described above is the ease of testing the device. Thus, if either TR1 or TR2 is removed from the circuit both lights will be turned off since neither TR1 nor TR2 will work without the other and either one can be tested by removing the other.
One hundred twenty-volt lamps or bulbs can be used with a standard 120 -volt AC power supply.
When both bulbs 12 and 13 are operative and have operative filaments, and the mechanical switch 18 is turned on, the gate circuit will be actuated first after which TR1 and TR2 will permit current flow between pins 2 and 1 so that the Walk light will actually turn on first although the speed of the entire circuit is so fast that the Don't light is actuated substantially simultaneously and a pedestrian will not be able to determine which light goes on first.
Turning now to the embodiment of FIG. 2, identical elements of the circuit arrangements 20 are numbered the same as corresponding elements in the embodiment of FIG. 1.
In embodiment 20, line 22 from pin 1 to line 23 interconnecting pin 1 of TR2 and bulb 12 is eliminated and pin 1 of TR1 is connected directly to Walk bulb 12 while pin 1 of TR2 is connected directly to Don't bulb 13. A resistor (preferably 10K resistor) 21 is provided between pins 1 and 3 of TR2 and switch 18 provides AC power to both pin 2 of TR1 and pin 2 of TR2. Resistor 19 in this embodiment is a 3.9K resistor. In this embodiment, TR1 does not carry the total current of both bulbs as is the case in the embodiment of FIG. 1. Moreover, if the Don't bulb is operative, it will be activated by AC current flow through TR2 even though the Walk bulb 12 may be inoperative due to the fact that passage of the current through the gate of TR2 is permitted since a gate current is established between switch 18, pins 2 and 3 of TR2, through 10K resistor 21 to pin 1 of TR2. If the Don't bulb 13 is burned out, TR2 can't turn on and pins 2 and 3 of TR2 have no voltage across them and no current flow is possible. Pins 3 and 2 of TR1 are at the same AC potential which keeps TR1 turned off in this case. When Don't bulb 13 is operative, there is a small voltage drop across TR2 so that TR1 will turn on. If the Walk light 12 is burned out, the Don't will still turn on since the Walk light is in parallel circuit arrangement to the Don't light and would not affect the working of the Don't light. This is so since there will still be a voltage difference between pins 2 and 3 of TR2 since the resistor 21 completes the gate circuit of TR2. In this embodiment, the gate circuits of TR1 and TR2 are in series with Don't bulb 13 but are not in series with each other as in the embodiment of FIG. 1. The circuit arrangement 20 accomplishes the same function as the circuit arrangement 10. Moreover, neither bilateral switch TR1 or TR2 carries the total current of both bulbs allowing the use of lower rated bilateral switch components.
Turning now to the embodiment of FIG. 3, an alternate circuit arrangement 30 is illustrated wherein corresponding parts of circuit arrangement 30 and circuit arrangements 10 and 20 are indicated by corresponding numbers.
In this embodiment, pin 1 of TR1 is grounded at 32, gate circuit resistor 19 is replaced by a resistor 31 connecting pin 3 of TR1 and pin 2 of TR2 and having a value of 2.6K. The lamp wiring in this embodiment is slightly more difficult than the embodiments of FIGS. 1 and 2 since one terminal of Walk bulb 12 is connected to AC positive while the other terminal is connected to pin 2 of TR1. AC positive current is supplied through switch 18 to pin 1 of TR2. The gate circuits of TR1 and TR2 are illustrated at FIG. 4 where the arrows represent current flow in the gate circuits of TR1 and TR2.
The Don't bulb 12 can be turned on if its filament is intact since there is a ground potential at pin 2 of TR2 which completes a gate circuit to pin 3 of TR2 through resistor 21 to pin 1 of TR2 which is at AC potential. In this case, a ground potential is applied to pin 2 of TR2 through resistor 31 to pin 3 of TR1 which completes a circuit between pins 1 and 2 of TR1 to bulb 12 thus turning on the Walk bulb 12. In this embodiment, each of the gate circuits of TR1 and TR2 are in series with the Don't bulb 13 but are not in series with each other. Thus, if the Don't bulb 13 is burned out, the Don't and Walk bulbs will be inoperative. If the Walk bulb is inoperative, the Don't bulb will still be actuated by the on-off switch 18. As in the embodiment of FIG. 2, the Don't bulb is in series with each of the gate circuits but the gate circuits are not in series with each other.
While specific embodiments of the present invention have been shown and described, it should be understood that many variations thereof are possible. For example, the specific values given for the solid-state switches, current supply and resistors can vary in different circuit arrangements. Other than standard 120- volt bulbs can be used. In some cases, the circuit arrangement can be used for response means other than bulbs such as bells, alarm signals, on-off control devices and the like.
In view of the many modifications possible, this invention is to be limited only by the spirit and scope of the appended claims.