Apparatus and method for relay control

Abstract: For use where there is a relay (42) controlling an AC power circuit to a load (20), such as a cooker heater, an optical sensor (64) observes arcing at the relay contacts (14). A control circuit (54) controls the time of subsequent actuation or deactuation of the relay with respect to the alternating current power circuit so that the relay contacts open or close substantially at a zero crossing point of the AC current, so as to minimise relay contact arcing.

Description: FIELD OF THE INVENTION This invention is directed to the control of a relay connected to a load, by controlling the operating or dropout point of the relay so that it opens or closes at a zero current point in the AC load circuit to eliminate arcing at the relay contacts. BACKGROUND OF THE INVENTION Current is delivered to an alternating current load through the contacts of a relay. When the load is to be switched off or on, the relay is actuated or deactuated. When the relay contacts open while current is flowing therethrough, an arc is drawn until the next zero current point, and this arc burns the relay contacts. Similar arcing occurs if contact closure is made at a non-zero current point. It is this arc burning of the relay contacts which reduces relay life. Accordingly, to achieve greater relay life, it is desirable to reduce or eliminate arcing upon the opening or closing of the relay contacts. US patent No. 4745515, on which the claims of this application are based, describes a relay control system which is intended to close the contacts of a relay in an AC power supply at zero current crossing points. The system senses zero voltage crossing points and energises the relay after a short time delay so as to close the contacts at a subsequent zero current crossing point. The time interval is based on the difference between two separate time intervals, T2 and T3. T2 is the time interval between a zero voltage crossing point, as detected by the system, and the next zero current crossing point. This time interval, as alleged in US 4745515, can either be zero or a quarter cycle of the AC frequency depending on whether the load to which the relay switches the AC current is resistive or inductive. In the control system described this time interval, T2, is a preset selected constant. T3 is the pull-in time, or lag, of the relay itself. This is measured automatically by the control system. Using T2 and T3 and the sensed zero voltage crossing points, the control system predicts at what time after a zero voltage crossing the next zero current crossing will be, subtracts T3, the relay pull-in time, and thus times the sending of an energisation signal to the relay. If T2 is preset correctly, the relay contacts should then actually close at a zero current crossing point. In the control system described in US 4745515 the preset time interval, T2, must be provided. As described in the introduction of US Patent No. 3265933, in a real application a load applied to an AC power supply relay may have voltage and current cycles out-of-phase by any angle depending on the inductive and resistive components of the load. In addition on switching-on an AC power supply, transient variations in phase difference and even non-sinusoidal waveforms may occur. The preset, constant T2 value of the system in US 4745515 can take no account of such variations. German patent application DE-A-3031517 describes a light sensor for detecting electric arcs in electrical apparatus such as switchgear, or for detecting fires in enclosed spaces. The sensor comprises a single optical fibre, one end of which is placed in an area for sensing light signals. A reflector is used to increase the field of view at the end of the fibre. The other end of the fibre is coupled to a light-detecting device. German patent no. 1146941 describes a power circuit comprising a switchable resistive bypass in parallel with a relay. The resistive bypass comprises a gas-filled triode connected in parallel with the relay, and a photodetector sensitive to light produced by arcing in the relay contacts and coupled to the central grid of the triode. The triode is normally non-conducting. When an arc occurs on opening the relay, the photodetector changes the voltage on the triode grid so that the triode conducts. A portion of the current in the relay is thus diverted from the arc, decreasing the intensity of the arc. When the arc extinguishes, the photodetector changes the grid voltage of the triode so that it is again non-conducting. SUMMARY OF THE INVENTION The invention provides apparatus and a method for the control of a relay as defined in the appendant independent claims. Preferred features of the invention are defined in dependent subclaims. In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is. directed to an apparatus and method for relay control which achieves minimized relay arcing by operating the relay so as to open or close its contacts at the zero current point in the AC load circuit. The method and apparatus include a device for observing and a means for measuring the time of arcing and a control circuit for receiving the relay open command signal and sending an operating command so that the relay opens or closes its contacts at or near the zero current point of the AC load circuit. It is, accordingly, an object and advantage of this invention to provide an apparatus and method for controlling a relay which supplies an alternating current load which maximizes relay life by minimizing arcing at the relay contacts when switching the load off or on. It is another object and advantage of this invention to provide an apparatus which has a radiation sensor positioned to receive radiation emitted from a relay contact arc and has a control circuit connected to the radiation sensor so as to shift the relay operating command to achieve relay contacts opening or closing at or near zero current crossing. The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description, taken in conjunction with the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an isometric view of an example of a relay installation, employing the method and apparatus for relay contacts or control in accordance with this invention. FIGURE 2 is an isometric view of a plug-in relay for use with the method and apparatus of this invention. FIGURE 3 shows a printed wiring board in which the relay of FIGURE 2 is plugged in, including part of the apparatus of this invention. FIGURE 4 is an isometric view of the sensor secured to the printed wiring board of FIGURE 3. FIGURE 5 is an enlarged side-elevational view of the relay on the printed wiring board with parts broken away. FIGURE 6 is an end-elevational view thereof with parts broken away. FIGURE 7 is an electrical schematic block diagram showing an apparatus embodying this invention. FIGURE 8 is a wave form diagram showing the current versus time and showing the relay command signal versus the same time base. DESCRIPTION OF THE PREFERRED EMBODIMENT The system for which the apparatus and method are intended and for which they improve operating life comprises an AC power source represented by lines 10 and 12 in FIGURE 7. Line 10 is connected to moving contact 14 which is connected to contact 16 upon closing of moving contact 14. The fixed contact 16 is connected by line 18 to a load 20. The load 20 may be any type of utilization circuit, including circuits having inductive and/or capacitive elements therein although, for convenience, the present invention will be described in connection with an inductive load. The utilization circuit 20 broadly represents any alternating current load. The utilization circuit is connected back to AC line 12 either directly, as indicated, or through additional contacts acting in parallel with the contacts 14 and 16. As is conventional in relays, a solenoid coil 22 has its plunger mechanically connected to the moving contact 14 so that electrical actuation of the coil causes actuation of the moving contact. For convenience of description of the conditions for and operation of the present invention, the relay illustrated in FIGURE 7 will be considered as "normally closed" in the sense that, when relay coil 22 is not energized, the contact 14 is closed as by a conventional spring (not shown). The relay can be constructed in the opposite manner so that, with deactuation of the coil, the contact will be opened by the spring and, in such a case, is a "normally open" contact. Command line 24 carries a signal to energize the solenoid and actuate the relay. In conventional systems, the command line 24 may be directly connected to relay coil 22 so that, when a signal is present, the coil is energized and the contacts are opened. FIGURE 8 represents by its curve 26 the current supplied in the AC lines 10 and 12. The current line 26 is optimally a sine wave and is shown in the single cycle in FIGURE 8, with a positive current pulse form 0 to 180 degrees and a negative current pulse from 180 to 360 degrees. A zero crossing of the current is achieved at 0, 180, and 360 degrees. The current curve is shown as an idealized sine wave in FIGURE 8 for convenience of illustration. The middle part of FIGURE 8 represents the voltage to relay coil 22 which, in this example, is of the "normally closed" type so that it requires actuation voltage to the relay to open the contacts. In its low state represented by line 28, the relay is closed. At the time represented by rising line 30, the voltage to relay 22 goes to the high state represented by line 32 and, after a very short period of time of less than a half cycle, the relay contacts are opened. As is well-known, when relay contacts are opened with current flowing therethrough, an arc is drawn, and this arc burns the relay contacts and reduces the life of the relay. In conventional circuits, there is no control over the actuation timing of the relay with respect to the current wave therethrough. Thus, the time 30 may occur at any point in the cycle between 0 and 360 degrees, and the chance that it will occur at one of the zero current crossings, such as indicated by line 27, is small. For this reason, the life of a conventional relay is greatly reduced. FIGURE 1 shows relays 34, 36 and 38 plugged into printed wiring board 40. The printed wiring board is a dielectric substrate carrying on one or both surfaces signal and load wiring for the relays plugged therein. Relay 42 is the same as relays 34, 36 and 38 and is shown in FIGURE 2 in a position where it is unplugged from the printed wiring board and, in FIGURES 3, 5 and 6, in a position where it is plugged into the printed wiring board. The relays 34, 36, 38 and 42 are examples of commercially available relays which can be employed in connection with the method and apparatus of this invention. The relay 42 contains the contacts 14 and 16 and coil 22. Relay pins 44 and 46 are connected to the coil and insert into board pin sockets 48 and 50, respectively. As is seen in FIGURES 1 and 3, pin socket 48 is connected to bus 52, which may connect to similar pin sockets with respect to other relays. The bus 52 is connected to control circuit 54 of this invention, generally indicated in FIGURE 7. The socket 50 is also connected to the control circuit 54 so that the control circuit controls the energization of pins 44 and 46 and, consequently, the energization of relay coil 22. Each relay on the baord is connected to be operated by the control circuit. The control circuit 54 is the control circuit for relay 42 and any other relays in its group. The pin 56 shown in FIGURE 2 is the lead 18 in FIGURE 7, which is connected to the fixed contact 16 and is connected to the utilization circuit. In the present instance, relay pin 56 is connected to the stationary contact of the relay and is received in socket 18 in FIGURE 3, which is part of the line to the utilization circuit. Relay pin 58 is connected to the moving contact of the relay and plugs into the socket 10 in FIGURE 3 which forms part of the alternating current line 10 seen in FIGURE 7. Relay 42 is thus a plug-in relay unit which plugs into corresponding sockets in the printed wiring board to receive actuation signals from the control lines in the printed wiring board and to control the flow of power in the power lines in the printed wiring board. Relay 42 and each of the other relays controlled in accordance with the apparatus and method of this invention has its contacts visible. In the relay 42, this is achieved by the provision of a window opening 60 in line with the relay contacts, as seen in FIGURES 5 and 6. The window opening may contain a convex lens 62 to collimate the optical emissions of arcing at the contacts. Positioned to receive the visible arcing emissions is a light-sensing semiconductor device 64. The light-sensing device is conveniently positioned on the lower side of baord 40. The board is provided with an opening 66 in alignment with the opening 60. As seen in FIGURE 7, the light-sensing device 64 sends a signal through line 68 to the control circuit with its signal corresponding to the arcing of the contacts 14 and 16. While a visible signal is described, arc radiation in other frequencies can be detected and employed as arc sensors. It should be noted that, with a sensor (such as light-sensing device 64 for example) at each relay, each relay can be controlling a load having different characteristics from the other loads, such as inductive or capacitive characteristics, and each relay is controlled for"no arc" at its load contacts. Referring to FIGURE 7, it is seen that the AC lines 10 and 12 also feed signal transformer 72 which has its secondary connected through a pair of IN 4004 (trademark) diodes 74 and 76. Both diodes are connected to the gate of MPS 6566 (trademark) transistor 78. The collector line 80 of the transistor has a high pulse at each voltage zero crossing of the supply lines 10 and 12. Connected between the signal transformer at the lines is full-wave rectifier bridge 82 which supplies power to regulator 84 which supplies voltage to the circuit. The input to rectifier 76 is also connected to the input of IN 4004 (Trade Mark) diode 85, which has its output connected through a network to the base of MPS 6566 (Trade Mark) transistor 86. The collector of transistor 86 and the signal line 80 are both connected to the base of MPS 6566 (Trade Mark) transistor 88. The function of this circuit is to cancel alternate pulses in line 80 and invert. The output signal in line 90 is high with a low pulse at alternate voltage zero crossings. The sensing device 64 shown in FIGURE 7 is a light-sensing LPT 80 (Trade Mark) photo-transistor, and as previously indicated, a plurality of such photo-transistors may be respectively observing a plurality of relay contacts for arcing. Several are shown, but the control circuit may control only a single relay and, in such a case, only one photo-transistor is required. On the other hand, while it is most convenient to observe the arc by means of its visible light output, other types of sensors may be alternatively employed, so long as they indicate the timing and duration of the arc. Line 68 is connected to the gate of MPS 6566 (Trade Mark) transistor 92, and the collector of this transistor is also connected to signal line 90. The result is that the signal in line 90 is held low for the duration of any arc observed by the sensor 64. Line 90 is connected to terminal 14 of 8039 (Trade Mark) microprocessor. Microprocessor 94 is programmed as a logic device. Whenever it is instructed to open a relay contact by a command signal in command line 24, the logic device actuates relay opening at a subsequent zero crossing indicated in line 90. If an arc is observed by the sensor 64, or companion sensor, the logic device measures the duration of the arc and places the duration information in memory for that relay. Each-subsequent relay opening command causes the logic device to look to the memory for that relay and add the remembered time to the zero voltage crossing point signalled by line 90 before actuating the relay by an actuation signal in line 44. Thus, the relay 42 is caused to open its contact 14 at a zero current crossing 27 (FIGURE 8) so that there is no opening arc. This results in long relay life. Referring again to FIGURE 8, the bottom waveform illustrates the voltage condition for drop-out operation of a "normally open" contacts relay, with the relay contacts closed at line 29, the voltage dropping at line 31, to the de-actuated relay voltage at line 33, and the contacts opening at zero current time line 27. As a particular utilization circuit, a 16 ampere, 230 volt "Calrod" (Registered Trade Mark) heater load is supplied through a suitable plug-in relay. Without the apparatus and method of this invention, the normally expected relay life is about 200,000 cycles. Since the contact burning rate is extremely small when the apparatus and method of this invention are employed, relay life under the same circumstances but with the inventive adjustment of the actuation point for no arcing, of about 5,000,000 cycles can be achieved without relay failure. The greater the current in the load circuit, the more arcing occurs with the consequence of more contact damage. The amount of arcing is a function of the load reactance. A purely resistive load would produce minimum relay contact damage, but even a "Calrod" (Registered Trade Mark) heater load is sufficiently inductive to cause relay contact damage of the amount noted above. Thus, different relay life improvement can be seen with different loads. In most relays, the pull-in or drop-out time changes slowly due to the amount of cycling required. Such is especially true in permanently connected equipment. For example, in the present case, the utilization circuitry 20 is considered to be the heater in a deep-fat fryer and the command signal in line 24 is a signal related to the deep-fat temperature so that the temperature of the deep fat can be carefully controlled. In other types of cooking or other utilizations, the command signal 24 may be a timing circuit which terminates power to the utilization circuit. In permanent or semi-permanent installations, circuit and equipment parameters change only slowly, and thus the observation of the arc need not be automatic but may be periodically done by the cooker operator, the manager, or maintenance personnel. In such manually adjusted equipment, the observer would make a manual adjustment on the control circuit to adjust the point at which energization of coil 22 occurs as a function of the current curve 26 so that the contact 14 opens at zero arc. It must be observed that the energization in lines 44 and 46 does not occur at 0, 180, or 360 degrees on the current wave, but occurs sufficiently before so that the contacts actually open at the zero point. In such a case, the control circuit 54 would be one in which a command signal is received in line 24 signalling the desire for relay opening, followed by an analysis of the voltage curve, and when the voltage curve reaches a predetermined point on its cycle, relay coil 22 is energized so that the moving contact opens when the current curve is at one of its zero points. The manual adjustment would adjust the point on the voltage curve at which the solenoid energization occurs. The automatic case is the same, but the arc is seen by a detector and the adjustment is automatically achieved. This invention has been described in its presently contemplated best mode, and it is clear that it is susceptible to numerous modifications, modes and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

Claims: The method of controlling a relay (42) which has contacts (14,16) for connection into an AC load line (10,12) and which has an actuation device for controlling the contacts, comprising the steps of: detecting the alternating voltage state at the point along the AC cycle at which the relay contacts are opened; observing or sensing radiation at the opening or closing of the contacts and when there is radiation; adjusting the time of relay opening or closing with respect to the AC wave to a different point on the AC wave so that the relay arcing radiation is minimized. The method of claim 1 wherein the adjusting step is automatically achieved in a control circuit (54) which receives a radiation signal, an AC wave signal and a relay opening command signal. The method of claim 1 wherein the radiation observation is achieved by visual viewing and the adjustment of the relay actuation signal with respect to the AC signal is achieved manually. The method of claim 1,2 or 3 including the previous step of connecting the relay to energize a cooking heater and connecting the command signal to a cooking signal source. The method of claim 2 wherein the radiation signal is provided by an arc radiation detector, which is an electronic detector, and the signal therefrom is connected to automatically adjust the relay actuation point with respect to the AC current wave. An apparatus comprising a control circuit for a relay in an AC line and a relay, comprising: a relay (42); a control circuit (54); command signal means (24)on said control circuit for signalling the actuation of the relay; actuation connection means (94) on said control circuit connected to the relay for opening or closing the contacts of the relay; and, voltage sensing means (86,88,90) sensitive to the voltage wave in the AC line for providing to said control circuit a timing reference for the AC line; characterised by; observation means for allowing an operator to observe electric arcing occurring during opening or closing of the relay contacts; and by adjustment means on said control circuit adjustable by said operator in response to observed arcing for controlling the actuation point of said actuation connection means relative to said timing reference so that relay arcing is minimised. The apparatus of claim 6, wherein said voltage sensing means senses zero voltage crossing points of the AC line for providing the timing reference. The apparatus of claim 6 or 7 wherein the relay has a solenoid (22) connected for actuation by said control circuit. The apparatus of claim 6,7 or 8 wherein said relay has a housing and there is an opening (60) in said housing in line with said contacts in said relay to allow observation of the contacts. The apparatus of any of claims 6 to 9 wherein there is a lens positioned to allow observation of the relay contacts. The apparatus of any of claims 6 to 10 wherein said control circuit is at least partially mounted on a circuitboard and the relay is plugged into said circuitboard with its contacts positioned to be observable. An apparatus for the control of a relay (42) in an AC line, comprising: a control circuit (54); command signal means (24) coupled to said control circuit for signalling the actuation of a relay; actuating means (94) connected to said control circuit for causing opening or closing of contacts (14,16) of the relay; and a voltage sensing means (86,88,90) sensitive-to the voltage in the AC line for providing to said control circuit a timing reference for the AC line; characterised in that; an arc sensor means is provided for detecting radiation emitted by an arc resulting from opening or closing the contacts of the relay; said control circuit includes an adjustment means responsive to said arc sensor means; and said control circuit is connected so that when a relay actuation signal is received from the command signal means and said control circuit causes opening of said relay contacts and an arc is detected by said arc sensor means, then said adjustment means operates to actuate the relay on subsequent relay actuation at a different actuation point with reference to the timing reference so that relay arcing radiation is minimised. The apparatus of claim 12, wherein the voltage sensing means senses zero voltage crossing points of the AC line. The apparatus of claim 12 or 13, wherein the arc sensor means comprises an arc sensor (64) connected to signal arcing to said control circuit. The apparatus of claim 14, wherein said arc sensor comprises a light-sensing device for receiving light emitted by an arc between the relay contacts. The apparatus of any of claims 12 to 15 for use with a relay having a housing in which an opening (60) is defined in line with the contacts in said relay, said opening in said housing being in alignment between said contacts and said arc sensor means so that arcing of said contacts can radiate to said sensor means. The apparatus of claim 16 wherein there is energy collection means in said opening in said housing, said energy collection means being for collecting energy radiated by contact arcing and for directing a portion of the arcing energy to said sensor means. The apparatus of any of claims 12 to 17, comprising a lens for collecting radiation emissions from relay contact arcing and directing them towards said arc sensor means. The apparatus of any of claims 12 to 18, wherein said control circuit is at least partially mounted on a circuitboard (40) and said circuitboard has sockets therein for the receipt thereon of a plug-in relay and said arc sensor means is mounted on said circuitboard. The apparatus of claim 9 wherein a relay is plugged into said circuitboard with its contacts positioned in detection relationship to said arc sensor means. The apparatus of any of preceding claims 12-20, in combination with a relay connected to said control circuit. The combination of claim 21 wherein a utilization circuit (20) is connected to said relay contacts, said utilization circuit being a cooking heater load and said command signal means connected to said control circuit being a cooking condition command signal. The combination of claim 22 wherein said cooking heater load is an electric cooking heater and said cooking condition command signal is a signal corresponding to adequate cooking temperature so that there is need to disconnect said cooking heater from an AC power supply.

Inventors: FLINDERS RONALD R, POLSTER LOUIS S, FLINDERS, RONALD R., POLSTER, LOUIS S.
Applicants: POLSTER LOUIS S, POLSTER, LOUIS S.
Application year: 1989
Main classification: H01H9
IPC codes: H01H47, H01H9, H02H1, H01H50