US3250951A - Photoelectric light control unit for load circuit - Google Patents

Description

May 10, 1966 T T 3,250,951

PHOTOELECTRIC LIGHT CONTROL UNIT FOR LOAD CIRCUIT Filed April 13, 1962 35 3:6 3 7 y 34- Hay-443 F/6.

l W 56* 25 A 26 A "II INVENTOR ,7 v0" 52 '5? MICHAEL A. mazr 5/ I BY fi L ATTORNEY United States Patent 3,250,951 PHOTOELECTRIC LIGHT CONTROL UNIT FOR LOAD CIRCUIT Michael A. Tabet, 1336 Ballentine Blvd., Norfolk 12, Va. Filed Apr. 13, 1962, Ser. No. 187,414 2 Claims. (Cl. 315-459) The present invention relates to a relay of the type wherein its contacts are normally closed and serves to complete a circuit from an electricalsource to a street lamp or lamps and the invention more specifically pertains to-improvernents in the contact arrangement and the mechanism for actuating the contacts of such a relay which are to be moved to positions opening the load circuit in response to an increase in the current flowing in a photoelectric element which controls the energization of the relay coil.

Units which consist of a photoelectric element and a relay have been extensively used in recent years for controlling the energization of street lamps and such control units are usually supported on the lamp fixture or the pole supporting the lamp. The relay has in the past been provided with but one set of contacts for interrupting the lamp load circuit when the resistance of a photoelectric element decreases in response to the natural light falling thereon to permit sufiicient current to flow in the coil of the relay to open the circuit to the lamp load. .A broad area cadmium sulphide photocell has been used to control energization of the coil of the relay without power increasing devices and such a photoelectric element serves to simplify the control unit. The power available from such a photocell is low and in a range below three hunwdred milliwatts. The contacts must be able to handle a a desired low resistance characteristic but such contacts tend to adhere or weld to each other as a consequence of the load current and the low contact pressures. Such contacts then tend to remain in engagement so that the load circuit is not interrupted when current flowing through the photoelectric element and the relay coil are at a maximum value such as occurs during full daylight. Thus a street lamp controlled by such a unit remains energized in the daytime and it has been necessary to remove and replace the defective device. When the relay is equipped with contactsformed of tungsten the tendency of the contacts to weld or adhere to each other is avoided but the contact pressures are limited by the capacity of the photocell and such contacts tend to oxidize or corrode to such an extent that when the contacts are moved to an engaged position with permissible contact pressure they often do not complete the load circuit at the voltages which areapplied to street lamps.

It is an object of the present invention to provide a relay for a light control unit wherein the energization of the coil is controlled by a photoelectric element with 3,250,951 Patented May 10, 1966 silver close to definitely complete the lamp load circuit and a relay wherein the contact formed principally of silver open first after which the tungsten contacts open to interrupt the lamp load circuit.

It is another object of the present invention to provide a relay equipped with dual contacts with one set formed of a metal having good electrical conductive character-. istics at low contact pressures with the other set formed of a metal having non-welding characteristics and to provide an operating mechanism whereby the contacts having the good electrical conductive characteristics open first and thereafter the other set of contacts open upon movement of the armtaure towards the core of the relay with the mechanism so constructed that the set of nonwelding contacts engage each other first upon deenergization of the relay coil and thereafter the set of contacts having goodelectrical conductive characteristics engage .each other;

A still further object of the invention is to provide a relay for a photoelectric control unit with two pairs of contacts and a mechanism in association therewith and with the armature of the relay which provides for snap action of the. contacts to provide positive switching even though there may be extremely minor changes in the level of light falling on the photoelectric element such as takes place at twilight.

Other objects and features of the invention will be appreciated and become apparent as the present disclosure proceeds and upon consideration of the accompanying drawing taken in connection with the following detailed description wherein an embodiment of the invention is disclosed.

In the drawing:

FIG. 1 is an enlarged perspective view of the relay showing the position of the parts in the deenergized condition.

FIG. 2 is a fragmentary side elevational view on a larger scale showing the parts in the intermediate position.

FIG. 3 is a view similar to FIG. 2 illustrating the open position of both sets of contacts.

FIG. 4 is a diagram showing a unit exhibiting the invention for controlling the energization of a lamp load.

A relay forthe control unit includes a coil 10 which embraces a core 11 in a conventional manner. The coil and the core are mounted in a frame formed of metal having good magnetic permeability characteristics and which maybe of U-shape and provided with two leg portions 12 and 14. The .core may be secured in the frame by means of a cap screw 16 so that the free end of the core provides a pole piece 17 (FIG 2). An isulating member 18- at each end of the coil provides protection for the winding and one serves to support terminals for the coil one of which is shown at 19 in FIG. 1. An armature indicated generally at 21 is mounted for swinging movements about a pivot pin 22 carried by brackets 23 mounted on the leg portion 14 of the frame. The armature has two arms to provide a bell crank lever with the arm 26 responding to the flux set up by the coil 10 whereas the arm 27 serves to'actuate the relay contacts as hereinafter described. These features as hereinabove described are of conventional construction.

A relatively rigid bar 28 is secured between blocks 29 contact 32 at the free end thereof as best shown in FIGS. 2 and 3. The bar 28 serves as a lead to the contact 32. A flexible leaf type spring blade 33 is mounted onthe frame of the relay by means of the blocks 29. The flexible blade 33 is formed of electrical conductive material and carries anothertungsten contact 34 at the free end thereof confronting the contact 32. The blade 33 is so formed and stressed that the contact 34 moves into engagement with the contact 32 when the coil is deenergized. The contacts 32 and 34 form one set or pair for the relay. The blade 33 carries another contact 36 of pure silver or an alloy consisting of silver at the free end thereof. Another leaf spring type blade 37 formed of electrical conductive material is supported between the insulating blocks 29 and carries a contact 38 which is formed of pure silver or an alloy consisting principally of pure silver. The contact 38 is supported in position confronting the contact 36 and the blade 37 is so formed and stressed that the contact 38 moves into engagement with the contact 36 in the deenergized condition of the coil 10.

A stud 41 formed of insulating material carries a pin 42 (FIG. 3) at one end thereof which projects freely through an opening in the arm 27 of the armature. An annular shoulder 43 is formed on the stud 41 and a pin 44 extends beyond the shoulder 43. The pin 44 extends through an opening in the blade 33 and the free end of the pin 44 is in abutting relationship with the resilient blade 37. The stud 44 is of such shape and dimensions that when the coil 10 of the relay is in a deenergized condition both sets of contacts engage each other as shown in FIGS. 1 and 4.

The relay equipped with such dual sets of contacts fulfills the objects of the invention and improves a unit for controlling the energization of a street lamp represented at 51 in FIG. 4 in response to the presence or absence of light falling on the photoelectric element 52 which is of the broad area cadmium sulphide type. The coil It is connected in series circuit relationship with the photoelectric element 52 and across a supply source 54 which is usually of a low voltage range. In the absence of daylight the resistance of the photoelectric element 52 is high and very little current flows in the coil 10 and both sets of contacts remain in engagement with each other. The lamp load circuit 56 is completed from one side of the source 54 through the set of contacts 36 and 38 and through the set of contacts 32 and 34.

When the level of light in the presence of the photo- 7 electric element 52 attains a predetermined value its resistance decreases so that sufiicient current flows in the coil 10 to influence movement of the arm 26 of the armature towards the pole piece 17. The intermediate position is shown in FIG. 2 where the free end of the pin 44 moves the contact 38 away from the contact 36. Thus the silver type contacts 36 and 38 having good electrical conductive characteristics but poor non-welding properties are first disengaged. The load circuit 56 however remains connected across the supply source 54 because the contacts 32 and 34 remain in engagement and because the shoulder 43 at the intermediate position of the armature does not engage the blade 33.

The contacts 32 and 34 open with snap action as the arm 26 is drawn towards the pole piece 17 from the position illustrated in FIG. 2. The shoulder 43 on the stud 41 engages the blade 33 during such movement of the armature 21 to separate the contacts 34 from the fixed contact 32. The small pin 44 continues to engage the blade 37 to maintain the contacts 36 and 38 in the disengaged relationship as shown in FIG. 3. The contacts 32 and 34 which are formed of tungsten and having the characteristic of resisting welding action serve to interrupt the load circuit 56. The lamp 51 is thus deenergized when light in the presence of the photoelectric element 52 is above a predetermined level.

The relaycoil 10 remains energized during daylight hours because sufiicient current continues to flow through the photoelectric element 52. As the level of natural light falls the resistance of the photoelectric element increases and the current flowing in the coil is not sufficient to maintain the contacts open. The resilient blades 33 and 37 then move the parts from the position shown in FIG. 3 to the position shown in FIG. 2. The shoulder 43' on the stud 41 is so disposed that the contact 34 engages the contact 32 while the contacts 36 and 38 remain out of engagement. In'the event that the tungsten contacts 32 and 34 become" oxidized or corroded to such an extent that the load circuit is not established therethrough at the permissible contact pressures the lamp 51 will not be energized. As the armature moves to the position shown in FIG. 1' the free end of the pin 44 on the stud 41 no longer applies force to the blade 37 so that the contact 38 moves into engagement with the contact 36. The silver type contacts 36 and 38 which are relieved of the possibility of welding during the opening of the load circuit serve to insure completion of the load circuit to the'lamp.

Such a relay equipped with dual sets of contacts having different electrical conductive characteristics and dilferent corrosion or oxidizing properties together with the operating mechanism between the armature and the contacts serves to fulfill the objects of the invention of avoiding faulty operation even though the contact pressures are low and the energy available through the photoelectric element is of limited values. Various changes may be made in the relay and the mounting of the contacts. Such modifications and others may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. A control unit for closing and opening a lamp load circuit in response to the absence and presence of natural light comprising, a source of current, a broad area cadmiurn sulphide type photoelectric element the resistance of which increases as light falling thereon decreases and having a capacity of less than three hundred milliwatts, a relay including a core and a coil thereon, means connecting said photoelectric element and said coil in series circuit relation-ship across said source, a first set of contacts formed principally of silver associated with said relay, spring means moving said first set of contacts into engagement with each other, a second set of contacts having tungsten therein, spring means moving said second set of contacts into engagement with each other, a movable amature associated with said core, means moved by said armature shifting said first set of contacts to the open position and thereafter moving the second set of contacts to the open position as the armature is moved by energization of said coil resulting from increased current fiowing through said coil as a consequence of a decrease in the resistance of said photoelectric element during a rise in the level of light falling thereon, and a lamp load circuit extending through both sets of said contacts from said source.

2. A control unit for closing and opening a load circuit in response to the absence and presence of natural light comprising, a source of current, a photoelectric element the resistance of which decreases as light falling thereon increases, a relay including a coil and an armature, means connecting said photoelectric element and said coil in series circuit relationship across said source, a first set of contacts having high electrical conductivity and low melting point characteristics associated with said relay, spring means moving said set of contatcs into engagement with each other, a second set of contacts having higher melting point characteristics than the first set of contacts, spring means moving said second set of contacts into engagement with each other, a load circuit extending from said source through both said sets of contacts, and means moved by said armature shifting said first set of contacts 5 e to the open position and thereafter shifting the second 2,039,230 4/ 1936 Lamb 315-15 9 X set of contacts to the open position as the armature is 2 0 093 1 937 Takjesen 10 rnoved by flux developed as a consequence of a decrease 2,199,394 5/1940 Dewan 315 159 X 1n the resistance of sand photoelectric element during a rise in the level of light falling thereon. 5 23771137 5/1945 Eaton 2OO 104'5 2,956,140 10/ 1960 Walter 200--104.1 References Cited by the Examiner UNITED STATES PATENTS GEORGE N. WESTBY, Primary Examiner.

1,618,816 2/1927 Davies 315-159 X 0.. PB LL, "r 1,788,111 1/1931 Knowles 315159X 1o R CAM E Examme'

Claims (1)

1. A CONTROL UNIT FOR CLOSING AND OPENING A LAMP LOAD CIRCUIT IN RESPONSE TO THE ABSENCE AND PRESENCE OF NATURAL LIGHT COMPRISING, A SOURCE OF CURRENT, A BROAD AREA CADMIUM SULPHIDE TYPE PHOTOELECTRIC ELEMENT THE RESISTANCE OF WHICH INCREASES AS LIGHT FALLING THE THEREIN DEREASES AND HAVING A CAPACITY OF LESS THAN THREE HUNDRED MILLIWATTS, A RELAY INCLUDING A CORE AND A COIL THEREON, MEANS CONNECTING SAID PHOTOELECTRIC ELEMENT AND SAID COIL IN SERIES CIRCUIT RELATIONSHIP ACROSS SAID SOURCE, A FIRST SET OF CONTACTS FORMED PRINCIPALLY OF SILVER ASSOCIATED WITH SAID RELAY, SPRING MEANS MOVING SAID FIRST SET OF CONTACTS INTO ENGAGEMENT WITH EACH OTHER, A SECOND SET OF CONTACTS HAVING TUNGSTEN THEREIN, SPRING MEANS MOVING SAID SECOND SET OF CONTACTS INTO ENGAGEMENT WITH EACH OTHER, A MOVABLE AMATURE ASSOCIATED WITH SAID CORE, MEANS MOVED BY SAID ARMATURE SHIFTING AND FIRST SET OF CONTACTS TO THE OPEN POSITION AN THEREAFTER MOVING THE SECOND SET OF CANTACTS TO THE OPEN POSITION AS THE ARMATURE IS MOVED BY ENERGIZATION OF SAID COIL RESULTING FROM INCREASED CURRENT FLOWING THROUGH SAID COIL AS A CONSEQUENCE OF A DECREASE IN THE RESISTANCE OF SAID PHOTOELECTRIC ELEMENT DURING A RISE IN THE LEVEL OF LIGHT FALLING THEREON, AND A LAMP LOAD CIRCUIT EXTENDING THROUGH BOTH SETS OF SAID CONTACT FROM SAID SOURCE.

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