US3560796A - Relay control system for prevention of contact erosion - Google Patents

Relay control system for prevention of contact erosion Download PDF

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Publication number
US3560796A
US3560796A US3560796DA US3560796A US 3560796 A US3560796 A US 3560796A US 3560796D A US3560796D A US 3560796DA US 3560796 A US3560796 A US 3560796A
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United States
Prior art keywords
relay
contact
control system
voltage
relay control
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Expired - Lifetime
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English (en)
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William R Landis
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Honeywell Inc
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Honeywell Inc
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
    • H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
    • H01H9/56—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere for ensuring operation of the switch at a predetermined point in the ac cycle
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/28—Modifications for introducing a time delay before switching
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/72—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices having more than two PN junctions; having more than three electrodes; having more than one electrode connected to the same conductivity region
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K3/00—Circuits for generating electric pulses; Monostable, bistable or multistable circuits
    • H03K3/02—Generators characterised by the type of circuit or by the means used for producing pulses
    • H03K3/35—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of bipolar semiconductor devices with more than two PN junctions, or more than three electrodes, or more than one electrode connected to the same conductivity region
    • H03K3/351—Generators characterised by the type of circuit or by the means used for producing pulses by the use, as active elements, of bipolar semiconductor devices with more than two PN junctions, or more than three electrodes, or more than one electrode connected to the same conductivity region the devices being unijunction transistors

Definitions

  • the bridge contains an impedance which unbalances the voltage ripple in such a manner as to provide for a predictable mode of synchronous switching.
  • the relay contacts are selected of dissimilar materials and operate with the predictable mode of synchronous switching so that there is little or no erosion of the contacts themselves.
  • the contact life is a function of many variables. It has been long recognized that in switching a direct current energized load, it is possible to extend the contact life of relay contacts by selecting the contact materials so that there is little or no transfer of contact materials from one contact member to another in the are that is drawn during the bounce of the contacts or in the contacts separation. This same technique is not normally applied to contacts for relays used to control alternating current loads as the bounce of the contacts and the opening of the contacts normally are not related to the voltage phase applied.
  • Synchronous switching of relay operated loads where solid state switches are utilized, normally is brought about by the alternating current ripple that is superimposed on the direct current average voltage of the power supply.
  • This ripple can be removed by the use of exceedingly large capacitors in the filtering network but in most cases this is an impractical approach to the problem.
  • This problem can also be solved by very carefully handpicking the diodes that are used to form the rectification means for the power supply, so that the ripple is very evenly balanced thereby eliminating the synchronous switching problem.
  • This solution also is very undesirable as the cost of handpicking and matching diode characteristics is prohibitive.
  • the present invention solves this problem very inexpensively and in a unique manner.
  • the present invention is directed to overcoming the detrimental effects of synchronous switching by in fact utilizing the synchronous switching phenomenon.
  • a resistor or similar type of impedance is added to one leg of a bridge that supplies a rectified direct current for the switching current.
  • the addition of the impedance unbalances the ripple voltage in a predetermined direction.
  • the addition of an impedance, such as a resistor adds very little cost and makes the ripple voltage from the rectifier bridge means consistently unbalanced in a defined or known manner.
  • the bridge could also be unbalanced by using diodes of different materials such as two silicon-type diodes and two germanium-type diodes in opposite legs of the bridge.
  • a diode could be used in place of the resistor. This unbalance is then utilized to cause a solid state switching circuit to synchronously switch at a defined point in the phase of the applied alternating current voltage. This switching then allows for the pull in and bounce of associated relay contacts to occur during a portion of the applied alternating current wave form such that little or no transfer of the contact material occurs in the arc.
  • one of the contacts is made of substantially pure tungsten.
  • the other contact material can be any other material that normally works with tungsten.
  • a typical example is silver cadmium oxide, Both tungsten and silver cadmium oxide contacts are well known and are given by way of example only.
  • FIG. 1 is a schematic representation of a simplified form of a bridge rectifier system and synchronous switching means to control a load by means of a relay;
  • FIG. 2 is a voltage-time graph of two of the voltages important to the present invention.
  • FIG. 3 is a graph of the relationship of the applied alternating current source voltage to the full wave rectified voltage and the synchronous switching voltages in the system.
  • An alternating current voltage source 10 is connected by conductors 11 and 12 to a transformer primary 13.
  • a control switch 14 is shown and can be any type of control means to supply energy to the primary winding 13 from the alternating voltage source 10.
  • a secondary winding 18 of the transformer is disclosed in the present application is a stepdown winding providing a low voltage on conductors 15 and 16 that is supplied to a rectifier means 20.
  • the rectifier means 20 includes a full wave bridge 21 including diodes 22, 23, 24, and 25. Connected in series with diode 25 is an impedance means 26 disclosed as a resistor.
  • the output of the full wave bridge 21 is on conductors 27 and 28 with conductor 28 being grounded at 30.
  • Also connected between conductors 27 and 28 is a filter capacitor 31 to filter out the majority of the variation in the half waves that are combined by the two conventional current paths through the diodes in providing a direct current supply for the system.
  • Conductors 27 and 28 are connected to a relay switching means 32 that is disclosed as including a resistor 34, a unijunction transistor 33 having terminal 12 connected to a first terminal of relay means 35.
  • the unijunction transistor 33 has its emitter 36 connected to one side 37 of a capacitor 38, the other side of the capacitor in turn is connected to conductor 28 that is common with the other terminal of relay means 35.
  • a solid state switching circuit portion of the relay switching means 32 is completed by a charging resistor 40 from the emitter to terminal b of unijunction 33.
  • the relay means 35 includes a relay coil 41 and pair of relay contacts 42 and 43.
  • the relay contact 42 will be referred to as the anode contact while the relay contact 43 will be referred to as the cathode contact for reasons that will become apparent in the description of the operation of the present system.
  • the relay coil 41 is electromagnetically linked to the contacts 42 and 43 to operate these contacts when energy flows in the relay coil 41, as is well known in the relay art.
  • a second set of relay holding contacts 48 and 49 are also operated with contacts 42 and 43 to hold the relay means 35 energized, once operated.
  • Relay contact 42 is connected by conductor 44 to the conductor l2 supplying energy to the system.
  • Contact 43 is connected by conductor 45 to load means 46 and conductor 47 which in turn is connected to the switch 14 to receive energy whenever the primary winding 13 receives energy.
  • the anode contact 42 of the relay means 35 is made of tungsten which has a very high melting point.
  • the relay contact 43, forming the cathode of the contact means is made of silver cadmium oxide, a common contact material used with tungsten to provide a noneroding contact structure when energy is applied across the contacts of a polarity so that the contact 42 is the anode and the contact 43 is the cathode.
  • the contacts 42 and 43 operate as if the device was connected to a direct little or no transfer occurs and the contacts do not erode.
  • the rectifier means 20 When the switch 14 is closed and energy is supplied through the transformer primary 13 to the transformer secondary 18, the rectifier means 20 has an average direct current output voltage developed across capacitor 31. Superimposed on the direct current output voltage is a ripple voltage that is normally present due to the fact that a sufficiently large capacitor 31 to eliminate all forms of ripple is impractical. Since the diodes 22, 23, 24, and 25 normally would have slightly different forward voltage drop characteristics, it is obvious that the ripple that is generated would be slightly unbalanced. To insure that the unbalance exists and is always in the same direction, a resistor or impedance means 26 has been placed in series with the diode 25.
  • the resistor 26 is selected to be large enough to always cause the unbalance in the ripple to be in the same direction or in a predetermined direction with respect to the phase of the alternating current voltage source. With this predictable unbalance, the relay switching means 32 can always be operated in a synchronous manner with respect to the phase of the applied alternating current voltage source 10.
  • the relay switching means 32 utilizes a conventional unijunction 33 along with a charging circuit made up of resistors 34 and 40 for the capacitor 38. As soon as the voltage across capacitor 38 reaches a predetermined point or the emitter 36 peak point voltage, the capacitor 38 discharges through the emitter 36 of the unijunction transistor 33 and the coil 41 of the relay means 35. Since the relay switching means 32 utilizes a solid state switch of the unijunction type, the operation of a synchronous nature, that is,'it always occurs at the same point of ripple voltage from the power supply on conductors 27 and 28.
  • the unbalance created by the addition of the resistor 26 insures that the unijunction 33 discharges the capacitor 38 during the same applied phase or wave form of the alternating current voltage source 10 and therefore the relay contacts 42 and 43 always come together during a predetermined phase of the alternating current voltage source.
  • any bouncethat occurs generates an arc that tries to transfer material from the tungsten electrode to the silver cadmium oxide electrode. Since the tungsten does not melt at the arcing temperatures, little or no transfer occurs and the contact fails to erode. This mode of operation is insured from device to device by the addition of the resistor 26 to the rectifier bridge 2, and the exact means of carrying this out will be described in connection with FIGS. 2 and 3.
  • FIG. 2 two wave forms of voltage 50 versus time 51 are disclosed.
  • An average direct current voltage 52 is shown and is the voltage normally considered the output voltage across the capacitor 31 of the circuit of FIG. 1.
  • An unbalanced superimposed ripple 53 is in reality present and has been exaggerated in size for clarity
  • the ripple voltage 53 is presented as seen on an oscilloscope used to view the voltages in a model of the invention.
  • the average direct current voltage 52 and its voltage ripple 53 are applied across a resistive system composed of resistor 34, the interbase resistance R of transistor 33, and the coil resistance of relay 41.
  • the resulting current through resistor 34, transistor 33, and relay consists of an average current and a ripple current having a wave form similar to that shown in FIG. 2.
  • This current causes a voltage to appear across the relay coil 41 and across the interbase resistance R of unijunction transistor 33 that is less in magnitude than the total voltage appearing across capacitor 31 butthat has an average voltage and ripple voltage wave form identical in shape but not size to that shown in FIG. 2.
  • the transistor 33 bias current is not enough to operate relay means 41.
  • the voltage appearing across relay 41 is added to a voltage within unijunction transistor 33 to establish the peak point voltage that capacitor 38 must charge to before conducting through emitter junction 36' of transistor 33. To repeat for clarity, the peak point voltage is not steady, but has the unbalanced ripple voltage superimposed on it.
  • FIG. 3 an enlarged representation of parts of FIG. 2 have been disclosed along with reference voltages as to the phase of the applied alternating current voltage source and the output of the full wave rectifier bridge 21.
  • a conventional alternating current voltage source wave form 60 is disclosed for reference. Aligned with the alternating current voltage source wave form 60 are the half wave cycle wave forms for the two halves of the rectifier bridge showing the one-half wave form cycle 61 with the resistor and the one-half wave cycle 62 without the resistor. It will be noted that the one-half of the cycle 61 with the resistor is slightly lower than the onehalf cycle wave form 62 without the resistor. This is the obvious result of unbalancingthe bridge 21 by the addition of the resistor 26.
  • Voltage 55 is the timing capacitor 38 charge voltage and is virtually free of voltage ripple.
  • the timing capacitor charge voltage is equal to or greater than the instantaneous peak point voltage
  • emitter 36 of transistor 33 will conduct and charge stored in capacitor 38 will flow through emitter 36 and lead b of transistor 33 into relay coil 41 pulling in relay 35.
  • the peak point voltage ripple 65 is unbalanced the unijunction transistor firing point 69 will always occur where ripple voltage 65 is minimum. It will be noted that this firing occurs during the one-half of the wave cycle 62 without the resistor 26 present. Due to the mechanical mass of the relay contact structure, there is alwaysa delay in the pull in or of the closing of the relay contacts 42 and 43.
  • the relay transfer time This is normally referred to as the relay transfer time and has been disclosed as a portion of the curve 65 occurring between points 63 and 64. If there is any bounce, it occurs subsequent to point 64 and has been shown as a contact bounce time 67.
  • the contact bounce time is short, and will be confined within the desired load voltage phase when contacts 42 and 43 close. Since the contacts 42 and 43 close during a predetermined phase of the applied alternating current voltage source if any bounce occurs, the arc can be made to exist with contact 42 being the anodemade of tungsten while the cathode is of a lower melting material such as silver cadmium oxide. As such, there is little or no transfer of material between thecontacts, and the contacts are subject only to the mechanical wear without the deterioration caused by the normal bounce. of conventional relay contacts.
  • the simple addition of a resistor to the conventional diode bridge circuit makes the operation of the relay contacts predictable from unit to unit and contact materials can be selected so that the application of a potential to a load does not create an arc which causes a transfer of the herent differences between the diodes 22, 23, 24, and 25, unless these diodes are handpicked and matched to have exactly the same characteristics.
  • the handpicking of conventional diodes is a very costly process.
  • the addition of a resistor 26 in a typical embodiment to which the present invention is applicable adds a cost of approximately $0.03 to the overall circuitry of the device.
  • the present invention takes advantage of the normal synchronous switching action of a relay switching means utilizing solid state devices.
  • a relay control system for energizing electrical load means during a predetermined phase of an alternating current voltage source to prevent erosion of relay contact means during the closure and subsequent bounce of the contact means, by the contact means being of dissimilar materials that resist erosion by the load current arc that is drawn at said predetermined phase of the alternating current voltage source including: rectifier means adapted to be connected to said alternating current voltage source and having a direct current output voltage with a superimposed ripple voltage; said rectifier means including means to unbalance said ripple voltage; relay switching means including relay means energized by said output voltage and synchronously switched by a voltage swing of said unbalanced ripple voltage; and said relay means having contact means of dissimilar materials to inhibit contact erosion upon said contact means bouncing during said predetermined phase of said alternating current voltage source; said load means adapted to be energized from said source by the operation of said relay contact means, with said contact means being synchronously operated with said alternating current voltage source by said unbalanced ripple voltage so that said relay contact means bounce during said phase of said source when said contact
  • a relay control system as described in claim 1 said bridge unbalancing means is a resistor.
  • relay control system as describedin claim 7 wherein said relay switching means is a solid state switching circuit.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Relay Circuits (AREA)
US3560796D 1969-12-11 1969-12-11 Relay control system for prevention of contact erosion Expired - Lifetime US3560796A (en)

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Application Number Priority Date Filing Date Title
US88421169A 1969-12-11 1969-12-11

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US3560796A true US3560796A (en) 1971-02-02

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US3560796D Expired - Lifetime US3560796A (en) 1969-12-11 1969-12-11 Relay control system for prevention of contact erosion

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US (1) US3560796A (ja)
JP (1) JPS5132343B1 (ja)
DE (1) DE2060511A1 (ja)
GB (1) GB1320358A (ja)
NL (1) NL7018131A (ja)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2281644A1 (fr) * 1974-08-07 1976-03-05 Fligue Wladimir Ensemble voltmetrique a relais electromagnetique
DE2753765A1 (de) * 1976-12-03 1978-07-06 Hitachi Ltd Relais-steuerschaltung
US4300032A (en) * 1975-10-02 1981-11-10 Matsushita Electric Industrial Co., Ltd. Output control apparatus for a microwave oven
US4873454A (en) * 1986-12-26 1989-10-10 Sam Sung Electronic Co. Ltd. Power source switching circuit
US4939776A (en) * 1988-09-20 1990-07-03 Siemens Transmission Systems, Inc. Logic signal circuit for a releasing relay
US5652691A (en) * 1986-05-30 1997-07-29 Robertshaw Controls Company Electrically operated control device and system for an appliance and method of operating the same
US20130119798A1 (en) * 2011-11-14 2013-05-16 Wei Song Methods and systems for cleaning relay contacts

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3372303A (en) * 1965-09-28 1968-03-05 Devetta Electronics Ltd F A. c. switch contacts
US3430063A (en) * 1966-09-30 1969-02-25 Nasa Solid state switch

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3372303A (en) * 1965-09-28 1968-03-05 Devetta Electronics Ltd F A. c. switch contacts
US3430063A (en) * 1966-09-30 1969-02-25 Nasa Solid state switch

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2281644A1 (fr) * 1974-08-07 1976-03-05 Fligue Wladimir Ensemble voltmetrique a relais electromagnetique
US4300032A (en) * 1975-10-02 1981-11-10 Matsushita Electric Industrial Co., Ltd. Output control apparatus for a microwave oven
DE2753765A1 (de) * 1976-12-03 1978-07-06 Hitachi Ltd Relais-steuerschaltung
US4153922A (en) * 1976-12-03 1979-05-08 Hitachi, Ltd. Relay control circuit
US5652691A (en) * 1986-05-30 1997-07-29 Robertshaw Controls Company Electrically operated control device and system for an appliance and method of operating the same
US4873454A (en) * 1986-12-26 1989-10-10 Sam Sung Electronic Co. Ltd. Power source switching circuit
US4939776A (en) * 1988-09-20 1990-07-03 Siemens Transmission Systems, Inc. Logic signal circuit for a releasing relay
US20130119798A1 (en) * 2011-11-14 2013-05-16 Wei Song Methods and systems for cleaning relay contacts
US9093885B2 (en) * 2011-11-14 2015-07-28 Regal Beloit America, Inc. Methods and systems for cleaning relay contacts

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GB1320358A (en) 1973-06-13
NL7018131A (ja) 1971-06-15
DE2060511A1 (de) 1971-07-08
JPS5132343B1 (ja) 1976-09-11

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