US3707634A - Apparatus for extending contact life of relays utilized for a.c. load switching - Google Patents

Abstract

Apparatus for use with a relay utilized to switch alternating current loads to extend the contact life thereof. Circuits are included to cause alternate energization of the relay to occur in time coincidence with points on the alternating current waveform that are 180* apart, respectively. Thus, the alternate operations of the relay occur at alternate polarities of the a.c. waveform switched. Hence, contact material transferred from one contact to the other during one relay operation is re-transferred from the other contact to the one on the next following relay operation.

Description

United States Patent Arlen et al.

1451 Dec. 2 6, 1972 [54] APPARATUS FOR EXTENDING CONTACT LIFE OF RELAYS UTILIZED FOR A.C. LOAD SWITCHING [72] Inventors: David Arlen, Jericho; Louis A. Guido, Northport; Lawrence P. Quinn, Glen Cove, all of NY.

[73] Assignee: Sperry Rand Corporation 22] Filed: A March31, 1971 21 Appl. No.: 129,771

52 7 us. c1 ..307/138 51 Int.Cl. ..H01h 1/50 [581 FicldofSearchj. ..307/l38;3l7/DlG.7,7,8

[56] References Cited UNITED STATES PATENTS 2,157,640 5/1939 Swarthout ..307/138 2,162,237 6/1939 Avery ..3l8/346 Primary Examiner-L. T. l-lix Attorney-S. C. Yeaton 7] ABSTRACT Apparatus for use with a relay utilized to switch alternating current loads to extend the contact life thereof. Circuits are included to cause alternate energization of the relay to occur in time coincidence with points on the alternating current waveform that are 180 apart, respectively. Thus, the alternate operations of the relay occur at alternate polarities of the a.c. waveform switched. Hence, contact material transferred from one contact to the other during one relay operation is rc-transferred from the other contact to the one on the next following relay operation.

- 6 Claims, 1 Drawing Figure x75 I l l LOAD 15 I RELAY I 1 I TIMING I l 14 cmcurrs 1 RELAY 32 OPERATIONS x COUNTER OF RELAYS UTILIZED FOR A.C. LOAD SWITCHING BACKGROUND OF THE INVENTION l. Field of the Invention The invention pertainsto electromechanical relays particularly with regard to circuits for extending the contact life thereof.

2. Description of the Prior Art It is known that the contact life of power switching relays utilized to control d.c. power is usually of short duration. This is because contact material transfers unidirectionally'from one contact to the other during the operation of the relay until contact failure occurs.

In apparatus powered by ac. waveforms such as sampled data systems, clocked systems, or other systems of a digital nature, the frequency of the power source is often used as the basic system timing means for reasons of economy or convenience. In systems of this type, power relay operations usually occur in time coherence with the ac. power waveform switched by the relay contacts. Therefore, the relays always operate at a predetermined phase angle or cyclic time of the'a.c. wave and consequently suffer the short duration contact life associated with the switching of dc. power.

In prior art power systems, such as servo mechanisms and other continuous signal systems v the relay switching of alternating current power signals often occurs randomly, that is the conditions that determine the switching are not related 'to the timing of. the current that is switched. In such systems a series of relay operations may occur at one polarity of the ac. waveform followed by a smaller number of operations at the opposite polarity of the waveform switched. Under such conditions a build up of material on one of the contacts may occur, unbalancing the structure of the relay to an extent sufficient to accelerate the rate at which material is transferred; hence again decreasing the contact life duration. Pitted contact surfaces are often observed in relays so operated.

In prior art systems of the type described, the relays may be operated at the zero crossings of the switched ac. power waveform in an attempt to extend the contact life. Although it is possible to determine the voltage zero crossing points with accuracy, it is difficult to arrange relay closure for these times. This is so because the procedure involves a consideration of the operating times of the relay which change substantially because of use and wear. Although the system may be designed for relay closure at the zero crossings of the power waveform, the closures may actually occur substantially off-zero thus decreasing contact life for the reasons given above with respect to synchronous relay operation.

SUMMARY OF THE INVENTION The above disadvantages in the prior art operation of relays for switching, for example, alternating power waveforms are obviated in accordance with the present invention by apparatus for extending relay contact life. The apparatus comprises first circuits for applying an energizing signal to the relay ata predetermined phase angle of the alternating current being switched. The apparatus further includes second circuits for applying the energizing signal to the relay at a phase angle that is displaced fromthe predetermined phase angle. Circuits responsive, for example, to the energizations of the relay are included for alternately actuating the first and second circuits for a predetermined number of energizations of the relay, respectively. By .these means, relay contact material is uniformly transferred and re-transferred between the contacts hence extending contact life as discussed above.

7 BRIEF DESCRIITION OF THE DRAWING The sole drawing is a schematic logic diagram partially in block form illustrating a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the sole FIGURE, a relay 10 is schematically illustrated including, for example, contacts 11 coupled in a conventional manner to a relay actuation coil 12. The relay 10 is connected to switch an ac. power waveform on a lead 13 through the contacts 11 to a load 14 and then to ground in response to relay energizing signals applied to a lead 15. The relay energizing signals on the lead 15 are provided by relay energizing circuits l6.

In systems of the type described above that derive their basic timing signals from the a.c. power line, the relay energizing signals on the lead 15 are applied to the coil 12 via the relay energizing circuits 16 at a particular phase angle of the ac. power waveform in accordance with the configuration of the circuits 16. Accordingly, the circuits 16 are schematically illustrated responsive to the alternating power signal on the lead 13. For example, the relay 10. may be utilized in digitally-timed control systems of the type utilized at roadway intersections for the actuation of vehicular traffic and pedestrian control signal lights. In such systems the relay. energizing circuits may comprise relay timing circuits 17 which are controlled by clock pulses from a clock pulse source 18. The clock pulse source 18 derives its basic timing from the a.c. power signal on the lead 13. The relay timing circuits 17 may, for example, comprise complex counter-decoder networks that provide timing energizing signals to the relay actuation coil 12 in response to the clock pulses from the source 18. Circuits of this type may be found, for example, in U.S. Pat. application Ser. No.'453,072 filed May 4, I965 in the name of John J. King entitled, Traffic Intersection and Other Signal Controllers Responsive to a Cyclic Pulse Train" assigned to the assignee of the presentinvention and now abandoned. The relay timing circuits 17 of the present invention may be instrumented by the interval counter 62 and the sequencer 65 of said Ser. No. 453,072 while the clock pulse source 18 of the present invention may be instrumented by the timer unit 66 of the said Ser. No. 453,072. A specific circuit for providing the clock pulses in response to the ac. power signal on the lead 13 is described in U.S. Pat. No. 3,379,980 issued Apr. 23, 1968 in the name of J. J. King entitled, Pulse Generator of Low Frequency .Rise Train Synchronous to High Frequency Clock Pulse Source and assigned to the assignee of the present invention.

It is thus appreciated from the foregoing that in the absence of the present invention the contacts 11 of the relay are always closed in response to the signal on.

the lead at the same polarity of the a.c. waveform on the lead 13. This results in a unidirectional transfer of material between the contacts 11 precipitating early contact failure as discussed above. The present invention embodies the principle of balanced operation on a relay cycle-to-cycle basis to achieve long contact life. The timing of the switching is controlled so that, for example, successive relay operations occur on opposite polarities of the a.c. waveform. The basic timing stability of a digital system of the type described in said Ser. No. 453,072 assures that successive operations of the relay 10 occur at the same amplitude of the a.c. waveform on opposite polarities thereof. The circuits which provide the required controlled reversal of switching times, in accordance with the present invention, will now be described.

The a.c. power waveform is applied to half-wave rectifying diode 21 via a terminal 22. The positive halfcycles of the a.c. power waveform at the terminal 22 are provided by the diode 21 to a scaling resistive voltage divider 23. The a.c. line voltage at the terminal 22 scaled by the network 23 to levels suitable for input to conventional logic circuits is applied as the input to an inverter 24. The inverter 24 provides a binary valued logic signal in response to the half-wave rectified a.c. power signal in a conventional manner. The binary valued logic signal from the inverter 24 is applied as the input to another inverter 25. The inverter 25 provides a signal that is the logical inverse of the signal provided by the inverter 24. It is thus appreciated that the inverters 24 and 25 provide binary ONE signals in response to the opposite polarity half-cycles of the a.c. waveform, respectively. For example, the inverter 24 provides a binary ONE when the a.c. power waveform is negative and a binary ZERO when the waveform is positive. Conversely, the inverter 25 provides a binary ONE when the a.c. waveform is positive and a binary ZERO when the a.c. waveform is negative.

The logic signal outputs from the inverters 24 and 25 are applied as inputs to NAND gates 26 and 27 respectively. The outputs of the NAND gates 26 and 27 are combinedin an OR gate 30 to provide a signal to the clock pulse source .18 for reasons to be discussed.

A lead 31 is coupled with the relay load 14 to provide pulse signals representative of the individual relay actuations. The signals on the lead 31 are applied to a relay operations counter 32 which in turn provides signals, in a conventional counter 32 which in turn provides signals, in a conventional manner, representative of a predetermined number of energizations of the relay 10. The relay operations counter 32 may be set by conventional means (now shown) to provide signals representative of any selected number of relay actuations. It is appreciated that if the selected number is one, the signals on the lead 31 may be utilized directly and the relay operations counter 32 eliminated.

The output of the counter 32 is applied to the toggle input of a flip-flop 33. The Q Output of the flip-flop 33 is connected as a control input to the NAND gate 27 and the 6 output of the flip-flop 33 is connected as a control input to the NAND gate 26. Thus when the flipflop 33 is in the Q state, the logic signal from the inverter 25 is transmitted through the NAND gate 27 and the OR gate 30 to the clock pulse source 18. Conversely, when the flip flop as is in the 6 state the logic signal from the inverter 24 is transmitted through the NAND gate 26 and the OR gate 30 and again to the clock pulse source 18; It is therefore appreciated that when the flip-flop 33 is in the Q state, a binary ONE logic signal is applied to the clock pulse source 18 during the positive half-cycles of the a.c. waveform at the terminal 22, and when the flip-flop 33 is in the Q state a binary ONE logic signal is applied to the clock pulse source 18 during the negative half-cycles of the a.c. waveform. The flip-flop 33 toggles between the Q and 6 states in response to successive signals from the relay operations counter 32. It is therefore understood that for a predetermined number of energizations of the-relay 10, binary ONE signals are applied to the clock pulse source 18 during the positive half-cycles of the a.c. waveform and during the next following predetermined number of relay energizations, binary ONE signals are applied to the clock pulse source 18 during the negative half-cycles of the a.c. waveform. As previously mentioned, the predetermined number is set by the relay operations counter 32. These binary ONE signals alternately applied to the clock pulse source 18 with respect to the positive and negative half-cycles of the a.c. waveform in accordance with alternately occurring predetermined numbers of relay actuations operate to extend the contact life of the relay 10 in a manner now to be explained.

In operation, the energizing circuits 16 provide the relay energizing signals on the lead 15 during the positive half-cycles of the a.c. waveform when the flip-flop 33 is in the Q state and during the negative half-cycles when the flip-flop 33 is in the 6 state. The energizing signals are applied during the respective half-cycles so that the relay contacts 1 1 are caused to close at respective phase angles of the a.c. waveform that are approximately l displaced from one another. The binary ONE levels, selected by the state of the flip-flop 33 and transmitted through the OR gate 30, cause the source 18 to provide clock pulses selectively at approximately zero degrees or at approximately in accordance with the flip-flop 33 being in the Q state or the state respectively. Generally, this may'readily be achieved in accordance with the circuits utilized to instrument the clock pulse source 18in any conventional manner.

Specifically for the clock pulse source disclosed in said US. Pat. No. 3,379,980, the transformer 10 of the said patent is removed and the signals from the OR gate 30 of the present invention are applied to set the flip-flop 11 of the patent. The signals from the OR gate 30 are applied through an inverter (not shown) to reset the flip-flop 11 of the patent. It is therefore appreciated that the clock pulses from the clock pulse source 18 are caused to occur at approximately 0 2r approximately 180 in accordance with the Q or the Q state of the flipflop 33, respectively. Thus, the relay timing circuits 1 7 of the type hereinabove' described provide the relay energizing signals on the lead 15 selectively at either approximately 0 or 180 in accordance with the state of the flip-flop 33. Because of the inherent delay in relay actuations, the relay contacts 11 will be caused to close at a particular phase angle in the positive half-cycles of the a.c. waveform when the flip-flop 33 is in the Q state and will be caused to close at a phase angle displaced approximately l80 from the particular phase mmn MA) angle when the flip-flop 33 is in the 6 state. Thus it is appreciated that because the flip-flop 33 alternates between the Q and Q states in response to alternately occurring predetermined numbers of relay operations, the relay contacts 11 will be caused to close at alternately occurring positive and negative voltages of equal magnitude. Thus contact material transferred from one contact to the other when the flip-flop is in the 0 state will be re-transferred from the other contact to the one when the flip-flop 33'is in the 6 state. Hence, it is appreciated, as previously described, that by the use of the present invention the operating life of the contacts 11 will be significantly extended with respect to the prior art method of relay switching described above. Typically, the flip-flip 33 may be toggled in response to alternate operations of the relay 10. Thus contact material will be transferred back and forth between the contacts as the relay l0 undergoes its successive operations.

From the foregoing it will be appreciated that the rectifier 2 1, the inverter 24, the gates 26 and 30 and the relay energizing circuits 16 comprise first means for applying the energizing signal on the lead 15 to the relay at a predetermined phase angle of the alternating current signal applied to the terminal 22. Furthermore from the foregoing, it will be appreciated that the rectifier 21, the inverters 24 and 25, the gates 27 and 30 and the relay energizing circuits 16 comprise second means for applying the energizing signal on the lead to the relay 10 at a phase angle of the alternating current signal approximately 180 phase displaced from the predetermined phase angle. It will also be appreciated from the foregoing that the relay operations counter 32 and the flip flop 33 comprise controlling means for alternately actuating the first and second means as described above for a predetermined number of energizations of the relay l0. 7 In practice, an even finish is developed on relay contact surfaces operated in accordance with the present invention which contributes to long relay contact life far in excess of that normally achieved by relays operated in accordance with prior art methods.

Although the present invention has been explained in terms of a timing control system, it is appreciated that an external relay energization command signal may be applied through appropriate circuits to energize the relay. The timing of the external command signal may be controlled by the output of the OR gate in a manner similar to that described above. It is furthermore appreciated that although the flip-flop 33 is caused to toggle in response to the operations of the relay 10, an external control signal related to the functioning of the system in which the relay 10 is included, may be utilized to toggle the flip-flop 33 to the same beneficial effect described above.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description a relay adapted to be responsive to an energizing signal for switchin analtematin current si a] com risin first mea s 21, 24, 2g, 30,16)% dr applying 55nd phase displaced from said predetermined phase angle, and

controlling rneans(32, 33) for alternately actuating said first and second means for a predetermined number of energizations of said relay respectively.

2. The apparatus of claim 1 in which said controlling.

means comprises bistable means (33) responsive to said energizations of said relay for alternately providing first and second control signals in response to said predetermined number of said energizations, respectively.

3. The apparatus of claim 2 in which said first means includes rectifying means (21) responsive to said alternating current signal for providing the half-cycles thereof of one polarity,

means (24) responsive to said half-cycles for providing a first logic signal in accordance therewith, first gating means (26, 30) coupled to receive said first logic signal and said first control signal for transmitting said first logic signal in response to said first control signal, and

relay energizing means (16) for applying said energizing signal to said relay at said predetermined phase angle in response to said transmitted first logic signal.

4.The apparatus of claim 3 in which said second means includes inverter means (25) responsive to said first logic signal for providing a second logic signal in accordance with the half-cycles of said alternating current signal of the polarity opposite said one polarity, and

second gating means (27, 30) coupled to receive said second logic signal and said second control signal for transmitting said second logic signal to said relay energizing means in response to said second control signal thereby applying said energizing signal to said relay at said phase angle approximately 180 phase displaced from said predetermined phase angle.

5. The apparatus of claim 1 in which said controlling means comprises counting means (32) responsive to said energizations of said relay for providing signals representative of said predetermined numbers thereof, and

bistable means (33) responsive to said counting means signals for alternately providing first and second control signals in response thereto, respectively.

6. The apparatus of claim 1 in which said controlling means comprises bistable means (33) responsive to said energizations of said relay for alternately providing first and second control signals inresponse to alternate energizations of said relay, respectively.

Claims (6)

1. Apparatus for extending the life of the contacts of a relay adapted to be responsive to an energizing signal for switching an alternating current signal comprising first means (21, 24, 26, 30, 16) for applying said energizing signal to said relay at a predetermined phase angle of said alternating current signal, second means (21, 24, 25, 27, 30, 16) for applying said energizing signal to said relay at a phase angle of said alternating current signal approximately 180* phase displaced from said predetermined phase angle, and controlling means (32, 33) for alternately actuating said first and second means for a predetermined number of energizations of said relay respectively.

2. The apparatus of claim 1 in which said controlling means comprises bistable means (33) responsive to said energizations of said relay for alternately providing first and second control signals in response to said predetermined number of said energizations, respectively.

3. The apparatus of claim 2 in which said first means includes rectifying means (21) responsive to said alternating current signal for providing the half-cycles thereof of one polarity, means (24) responsive to said half-cycles for providing a first logic signal in accordance therewith, first gating means (26, 30) coupled to receive said first logic signal and said first control signal for transmitting said first logic signal in response to said first control signal, and relay energizing means (16) for applying said energizing signal to said relay at said predetermined phase angle in response to said transmitted first logic signal.

4. The apparatus of claim 3 in which said second means includes inverter means (25) responsive to said first logic signal for providing a second logic signal in accordance with the half-cycles of said alternating current signal of the polarity opposite said one pOlarity, and second gating means (27, 30) coupled to receive said second logic signal and said second control signal for transmitting said second logic signal to said relay energizing means in response to said second control signal thereby applying said energizing signal to said relay at said phase angle approximately 180* phase displaced from said predetermined phase angle.

5. The apparatus of claim 1 in which said controlling means comprises counting means (32) responsive to said energizations of said relay for providing signals representative of said predetermined numbers thereof, and bistable means (33) responsive to said counting means signals for alternately providing first and second control signals in response thereto, respectively.

6. The apparatus of claim 1 in which said controlling means comprises bistable means (33) responsive to said energizations of said relay for alternately providing first and second control signals in response to alternate energizations of said relay, respectively.

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