US3335331A - Relay system - Google Patents

Description

Aug. 8, 1967 s. s. PRESSMAN RELAY SYSTEM Filed March 26, 1964 BNP) n H 3 A o D v D a .A

im@ Ixo@ United States Patent M Electronics Corp., Floral Park, N.Y., a corporation of New York Filed Mar. 26, 1964, Ser. No. 354,859 8 Claims. (Cl. 317-124) The present invention relates generally to relay circuits and more particularly to series resonant relay circuits which require no unilateral control devices for their operation, and which are operative over a wide range of standard supply voltages with little or no deleterious effects on operating characteristics.

Many applications exist for relay controls, wherein current to a load is controlled by a relay which changes its operative state in response to an activating element which senses a physical magnitude and which changes impedance as a consequence of such sensing. One typical application of this type relates to the operation of relays in `response to changes of light intensity, in which case the activating element may be a photo-electric cell, or more specically a photo-electric cell of the photo-conductive type. Alternative systems involve activating elements which are sensitive to temperature and which change resistance upon change in temperature. More generally, the activating element may be an impedance which is controlled by the value of a physical quantity. Throughout such applications of relay controls, the control circuit may be required to operate in physical areas in which several different supply voltages are available. Previously, where relay controls were required to transfer power from a source to a load, it was necessary to utilize a different control circuit for each particular value of standard line voltage which might be available in the particular area where such use occurred.

The present invention concerns itself primarily with relay controls wherein uniform operating characteristics prevail over a wide range of supply voltages, i.e., those voltages which are to be supplied tothe load, and wherein the activating element is of the photo-conductive type, although as to the latter it is to be realized that in its broadest aspect it is not so limited but may be utilized in conjunction with any type of Variable impedance as an activating element. For example, capacitive elements are known which are light sensitive and inductive elements of the saturating type are known which change rmpedance, or reactance, upon change of control current applied thereto, either of these types being among alternative elements which may be used in the control circuit.

Activating elements usually are of a type which cannot carry heavy currents, or, in the alternative, are of types which can be manufactured much more economically if made to have extremely small current carrying capacity. For example, the photo-conductor element is not normally capable of carrying heavy currents when fabricated in convenient size, and a saturable inductance may be reduced in size as the current required to be controlled by it is reduced. It is a feature of the present invention to provide a control circuit for a relay, control being effected in response to an activating element which is not required to draw heavy current or to be of considerable size, and in which the relay is controlled directly by the activating element without requiring the interposition of an amplifying device, such as a vacuum tube, a transistor, or the like. Thereby, the cost of a relay system may be radically reduced, and its reliability under long term operating conditions may be radically increased. A primary feature of the present invention resides in the capability of the control circuit to operate uniformly in transferring power from an A-C source to 3,335,331 Patented Aug. 8, 1967 a load over a relatively wide range of supply voltages which may be encountered in practical applications, Without need for modification of the control circuit structure. Thereby, where a conversion in voltage level of the A-C power supply is desired or necessary, the relay control circuit embodiment of the present invention may be left unaltered in the system under conversion. Further, there may be eliminated any requirement for maintaining a stock inventory of various relay controls for use with a plurality of supply voltage levels. Still further, the present relay control is relatively uneflected by wide fluctuations in voltage from the A-C power supply line, as commonly occur, for example, on electric utility supply lines.

Briefly describing a preferred embodiment of the invention, a relay coil having a saturable magnetic flux path is connected in series with a capacitor, with which it resonates or approximately resonates at the operating frequency of the system, i.e., the A-C frequency of the power supply. The present system is designed and intended primarily for energization from power lines, i.e., at 60 c.p.s. The activating element, which in the preferred embodiment of the invention is a photo-conductive cell, is connected preferably across the relay coil, although it may alternatively be connected across the capacitor. In the absence of light the photo-conductive element has an extremely high resistance, and accordingly does not materially effect the series circuit consisting of the tuning capacitor and the relay coil. However, when the photoconductive element is illuminated, the Q of the series circuit, i.e., the ratio of inductive reactance to circuit resistance, is reduced, and this reduction may be radical. Accordingly, the total voltage across the relay coil, which is higher than line voltage under resonant or near resonant condition, may be reduced by reduction of the Q of the circuit to a comparatively low value, so that the relay switches from an operating to a nonoperating condition. The effect of the photo-conductive cell on the Q of the circuit is enhanced so far as current drawn by the relay coil is concerned, by the fact that the photoconductive element shunts the relay coil and that the shunting effect is relatively slight when the photo-conductive cell is unilluminated but becomes considerable when the photo-conductive cell is illuminated. Nevertheless, the photo-conductive cell is not required to pass relay current, so that a heavy relay may be operated by means of the present circuit in response to a photo-conductive cell which is small and of low cost. Furthermore, the life of the photo-conductive cell is lengthened by the fact that it is not required to carry heavy currents. As an alternative circuit arrangement, the photo-conductive element may be connected across the tuning capacitor instead of across the relay coil, in which case illumination of the photo-conductive element changes the Q of the resonant circuit and thereby is able to control operation of the relay. However, the total eect in the latter case is smaller than when the photo-conductive element is connected directly across the relay, because the shunting effect is lost.

In accordance with the present invention, the operating point on the saturation curve of the voltage responsive relay is selected to be in the saturation region to maintain operating coil voltage relatively invariant over a wide range of supply line voltage. For example, power supply line voltage commonly encountered in practice may be either volts or 240 volts, at 60 c.p.s. With the pre.- ferred embodiment of the control circuit, briefly described above, connected across the line, an increase of activating element resistance upon reduction of intensity of light impinging thereon, results in an increase of resonant circuit Q and a consequent gradual increase in coil voltage. Thus relay coil pull-in begins at a particular point along the saturation curve irrespective of line voltage provided the latter is sufficiently high to produce minimum operating coil voltage. This beginning condition of pull-in is set near the bend, i.e., the knee, of the relay saturation curve. At pull-in there is an abrupt change in relay coil impedance, as will hereinafter be more fully explained, as flux density saturation begins to occur in the magnetic path. For 120 volt line voltage, operation takes place largely in the saturation region where coil reactance, although decreased slightly from the value attained at the previously mentioned abrupt change, is still relatively high, and the resonant condition obtains. When 240 volt line voltage operation is required, the control circuit action is similar to that described above except that relay operation takes place even further into the relay saturation region. At this operating point coil reactance is well below the value existing at 120 volt operation, the resonant circuit is detuned, and thus the relay coil voltage is closely similar to that which existed in the former case. Because there iS only slight difference in coil voltage at either supply line voltage, and over a broad range which includes the two standard line voltages specified, it follows that operating characteristics of the control circuit are maintained substantially invariant. The importance of this feature is dernonstrated by the fact that no circuit modification is required for installation in power systems utilizing either supply line voltage. In addition, relay control circuit removal from the system is not required should there be conversion from one line voltage to the other. Further, uniformity of operation with respect to illumination level is maintained despite rather rapid changes in impedance of the activating element, for example a photo-conductive element, at low illumination levels.

It is accordingly a broad object of the present invention to provide a relay system having uniform operating characteristics over a wide range of supply voltage levels, in which the relay coil is contained in a series resonant circuit, and in which a variable impedance is associated with the series resonant circuit in such fashion as to effect the Q of the resonant circuit, upon change in value of the impedance element, suiciently to change the operating state of the relay, and in which the relay coil operating Voltage varies only slightly irrespective of line voltage level changes over a relatively wide range, by virtue of relay operation in the saturation region.

It is a more specilic object of the present invention to provide a relay circuit having relatively invariant operating characteristics in transferring power from a supply line to a load irrespective of changes of voltage level of the supply line across which the relay circuit is connected, in which the relay coil is contained in a series resonant circuit and in which a variable impedance is associated with the series resonant circuit in such manner as to affect the Q of the resonant circuit upon change of value of the impedance element, and in which the relay coil reactance varies inversely with supply line voltage because of relay operation within the flux satuartion region so as to produce a relatively constant relay coil operating voltage over a wide range of supply line voltage levels.

A further object of the invention resides in the provision of a relay system for uniform operation irrespective of wide variation in supply voltage to the relay system, in

which the relay coil is located in series circuit with a tuning capacitance, for series resonant operation, and in which a variable impedance is associated with the series resonant circuit in such fashion as to affect the Q of the resonant circuit upon change of the impedance value of the impedance element, and in which the operating point of the relay is preselected to occur in the region of flux density saturation of the relay saturation curve, whereby increases in supply line voltage will drive the relay further into its saturation lregion with resultant lowering of relay coil reactance and a consequent detuning of the series resonant circuit, maintaining relay coil operating voltage at a substantially invariant level.

The above and still further objects, features, and attendant advantages of the present invention will become apparent upon consideration of the following detailed description of one specilic embodiment thereof, especially when taken in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a schematic circuit diagram of a relay control circuit in accordance with an embodiment of the present invention.

FIGURE 2 is a graph showing characteristics of a photocell of the type which may be used in the embodiment of FIGURE l;

FIGURE 3 is a graph showing relay coil characteristics exemplary of the relay coil of FIGURE l; and

FIGURE 4 is a graph indicative of conventional relay operating characteristics of prior art relay circuits.

This application is related to the subject matter of copending application Ser. No. 851,352, led Nov. 6, 1959, assigned to the same assignee as the present invention.

Referring to FIGURE 1 of the accompanying drawing, the reference numeral 10' denotes a source of line voltage across which a relay coil 12 and capacitor 16 are connected in series circuit. In a preferred embodiment of the invention the line voltage source may have an A-C frequency of 60 c.p.s. Relay coil 12 and capacitor 16 are of the proper characteristics to form` a series resonant circuit at the frequency of the power line. Therefore, it follows that the total current llow to the relay coil 12 will be greater than would be the case in the absence of the capacitor 16, and that the voltage across the 4coil 12 will be ,greater than the line voltalge by a factor dependent upon the Q of the resonant circuit. The Q of the circuit is primarily determine-d by the resistance of relay coil 12, and more accurately in terms of the ratio of coil inductive reactance to coil resistance at the operating frequency. Connected directly across coil 12 is a photo-conductive cell 15. When the photo-conductive element 15 is suiciently illuminated, as may -be noted from consideration of the photocell characteristics of FIGURE 2 which are exemplary of photocells generally, the resistance across relay coil 12 becomes relatively small and the series circuit Q is reduced. On the other hand, when the photocell is relatively unilluminated the resistance thereof is sufficiently high to result in very little effect upon the Q of the series resonant circuit, as determined by relay coil 12.

That is, in the case of low photocell resistance, the phase of the voltage across the capacitor 16 is no longer opposite the phase of the voltage across relay coil 12, and moreover the relative magnitudes' of the two voltages becomeunequal, which may be described as reducing the Q of the resonant circuit. Therefore, in the operation of the relay control circuit of FIGURE l, when the photocell is in a relatively illuminated state, i.e. its resistance relatively low, the relay coil voltage is not of sutlicient level to cause operation of the normally open contacts 14 of the relay. As the light intensity decreases, the series resonant circuit Q increases and there is a corresponding increase in the voltage across relay coil 12. Eventually, as the photocell becomes unilluminated the coil voltage reaches a value suicient to cause operation of contacts 14. Thereupon the line voltage is connected directly `across the load which may, for example, be a plurality of lamps.

In order to provide damping eifects in the photo-conductive element path to prevent relay operation should the photocell 15 become illuminated for a short instant of time, a separate element (not shown), for example a ther-mister, which has the characteristics of gradual resistance change with current flow heating may be connected in series circuit with the photocell. Thus a delay would be provided to .prevent transient effects as might occur, for example, if ay flash of light were projected upon the photoconductive element.

As previously noted, in installing a system according to the present invention, the supply voltages encountered may differ according to the physical environment, that is the geographical area, in which the relay system is to be utilized. Thus, for example, in a street lighting system wherein the present invention may be used to provide street light illumination control by selectively connecting the energizing line voltage to the load on approach of night fall, a 12() volt or a 240 volt A-C line voltage may be provided. Operation of the relay system, however, is such that no modification of the relay control circuit is necessary for use over a relatively wide range of line voltage including 120 volts and 240 volts. This relatively invariant operation despite wide differences in supply voltage may be understood by reference to FIGURE 3, illustrating the operating characteristic curve of relay coil voltage vs. current, which curve is largely dependent upon the characteristics of the magnetic flux path of the relay and as such is also representative of relay magnetization curve. As a further aid to the understanding of the relay operation, a second curve showing relay coil impedance vs. coil current is Super-imposed on the graph of FIG- URE 3.

Referring now to FIGURE 3 as the resistance of photoconductive element 15 increases with decreasing light intensity, for example as darkness-falls, there is an accompanying gradual increase in voltage across the relay coil, caused by the increase in the series resonant circuit Q and the multiplying effects upon coil voltage thereof, irrespective of whether supply line voltage is 120 volts or 240 volts. Therefore in either case the relay armature 13 begins to pull in near the knee of the saturation curve, decreasing the air gap between armature and relay core and thus decreasing the reluctance in the magnetic path. Because the greatest portion of magnetomotive force produced by the relay coil current was used in driving t-he flux across the air gap, i.e., a high reluctance path, the rapid decrease in air ga-p and its subsequent elimination results in a rapid decrease in reluctance, and increase in flux density, and a sharp rise in coil reactance as depicted by the relatively vertical line in the curve indicating coil impedance vs. coil current. At this point the magnetic path begins to saturate, that is flux density increases rapidly, as shown by the rapid.decrease in slope of the saturation curve, i.e., the curve of coil voltage vs. coil current, and there is t-hus a consequent reduction in coil reactance, shown by the coil impedance characteristics.

The series circuit of relay coil 1,2 and capacitor 16 is tuned for resonance at the A-C frequency supply line Voltage, i.e., the impedance of the relay coil 12 and capacitor 16 are counter balanced because of the phase difference in the relatively high voltages across each of these elements and specifically a difference in phase of approximately 180. As previously noted, the relay coil voltage is dependent upon the value of Q `in terms of a multiplication factor times line voltage. As may be seen from FIGURE 3, relay operation at t-he 120 volt line level is set to occur Within the saturation region of the magnetic flux path, that is, along the relatively decreasing slope portion of the coil voltage vs. coil current curve.

-Upon reaching a .preselected operating coil voltage, relay operation occurs in a reliable and positive manner.

Should the relay system be used in conjunction with a supply line voltage of 240 volts there is no need for circuit modiiication because the relay coil voltage remains nearly the same as existed in the previous case. In 240 volt operation, relay circuit action through coil pull-in remains substantially similar to that which occurred at 120 volt line voltage. However, at the 240 volt level the relay is driven even further into the saturation region of the magnetic fiux path, as noted in the curve of coil voltage vs. coil current. Reliable relay operation, however, is preselected to occur in this further saturation condition. The series circuit of capacitor 16 and relay coil 12 is at this point no longer resonant, i.e., is detuned, as a result of the decrease in the relay coil inductive reactance because of the increased saturation of the magnetic circuit. The major impedance in the series circuit is thus-the capacitive reactance, and a substantial voltage appears across capacitor 16. However, coil voltage has increased only slightly from its value as existed at 120 volts because of the decrease in coil reactance.

Thus, the doubling of supply line voltage presents no significant change in the operating characteristics of the relay system. Such uniformity of operation allows a single relay circuit to be stocked for use in power supply systems, irrespective of the possibility of wide variations in line voltages. In a test of a relay control circuit constructed in accordance with the foregoing description, substantially invariant operation was obtained over a line voltage range from 110 volts to 277 volts. Itis to be realized that reliable relay operation may be preselected at any point within this range and not merely at the particular voltages which have been specified. A suitable relay for use inthe relay control system described is the type designated RL-1800-4 manufactured by Joseph Pollack Corporation, Aetna Motor Products Company, of Boston, Mass.

The graph of FIGURE 4 is typical of the characteristics of conventional relays employed in relay control circuits of the prior art. Consideration of the curves of relay coil voltage vs. coil current and of relay coil impedance vs. coil current of such prior art control circuits will show that circuit operating characteristics vary directly with line voltage changes. Except for the slight fluctuations occurring at relay coil pull-in, neither the slope of the relay coil Voltage curve nor that of the relay coil reactance curve varies significantly from a constant value. Thus, for example, if a control circuit incorporating a relay having the characteristics depicted in FIGURE 4 for use in a 120 volt power supply system were used in a 240 volt supply system, without extensive circuit modification, the large change in -relay coil operating voltage at the higher line voltage would result in completely unreliable operation. In the curve shown, a increase in line voltage represents a 93% increase in coil voltage. Further, such a relay for use at the higher voltage would be inoperative at the lower line voltage. Thus the value of relay operation in the flux density saturation region of the relay magnetic path to provide uniformity of control circuit operating characteristics irrespective of line voltage level changes, as is effected by the present invention, is readily appreciated. It is to be further noted that where iiuctuations occur in the supply line voltage the prior art relay control circuit would be incapable of positive and reliable operation but instead the relay contacts would chatter, i.e., make and break, according to the resulting variations in relay coil voltage.

While the preferred embodiment of the present invention has been described as utilizing the photo-conductive cell 15 as the activating element of the system, it will be appreciated that any variable resistance may be substituted therefor, exemplary elements being heat sensitive resistances, light sensitive capacitors, current sensitive conductors, and the like. So long as the element substituted for the photo-conductive element 15 can be varied between a very high value of impedance and a very low Value of impedance, the Q of the series circuit comprising the capacitor 16 and the relay coil 12 can be radically modified, and the system will operate effectively. In any of these cases, moreover, the activating element, with or without a transient damping element, constitutes a shunt across the relay coil 12 and accordingly has a control effect which is cumulative to the control effect contributed by the series resonant circuit as such, so that the two cumulative effects can more positively control the voltage across relay coil 12 than is the case for either effect alone. Further, the use of the saturated magnetic flux region of the relay operating characteristics allows invariant operation over the previously noted wide range supply line voltages, assuring positive and reliable control, and as- 7 suring that the system will not chatter despite changes in the supply voltage.

While there has been described and illustrated one specific embodiment of the present invention, it will be clear that variations of the details and structure which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A control circuit for connecting an A-C power supply line to a load, said control circuit adapted for uniforrn operation over a relatively wide range of line voltages, comprising, in combination, a relay having an induction coil and a saturable magnetic path, a capacitor connected in series circuit with said coil to form a resonant circuit across the supply line, an activating element having an impedance which varies in response to changes in ambient light intensity, means connecting said activating element in parallel circuit with one of said resonant elements so that said activating element controls the current passing through said coil to modify the Q of said resonant circuit when the ambient light intensity on the activating element changes, said relay including means effective to connect said line to said load upon the condition of a predetermined voltage across said relay coil, said relay having preselected operating points solely in the condition of saturation of the relay magnetic flux path whereby the operating voltage across said relay coil is maintained substantially invariant over said relatively wide range of line voltages.

2. The combination according to claim 1 wherein said activating element is a photo-conductive cell.

3. A relay system for uniform operation in transferring A-C power from a source to a load over a wide range of standard source voltages, said system comprising a relay having at least a relay coil, a saturable magnetic flux path, and a pair of contacts; a4 capacitive reactance connected in series circuit with said relay coil across said source, said series circuit having a resonant condition at the A-C frequency of said source; said pair of contacts connected between said source and said load and adapted to transfer power therebetween upon operation of said relay as defined by a predetermined voltage level across said relay coil; said relay having a plurality of preselected operating points within said range of standard source voltages; a first of said plurality of preselected operating points at the lowest of said range of source voltages at which said series circuit is in resonance and said magnetic path is saturated; a second of said plurality of preselected operating points at the highest of said range yof said voltages, at which said magnetic path is further saturated whereby the inductive reactance of said relay coil is gradually reduced in value from that at said first operating point and said series circuit is detuned; said magnetic path being increasingly saturated as said source voltage is increased from said lowest to said highest voltage level; said gradual reduction in coil reactance being effective to maintain said coil voltage at substantially said predetermined level throughout said range of source voltages; said series circuit having a Q greater than unity; and variable impedance means shunting one of said capacitive reactance and said relay coil for controllably modifying said Q value.

4. The combination according to claim 3 wherein said variable impedance is a photo-conductive cell.

5. A relay control circuit for transferring A-C power from a source to a load, comprising, in combination, a relay having an induction coil and a saturable magnetic path; a capacitive reactance connected in series circuit with said coil to form a series resonant circuit across the source; said series circuit having a resonant condition at the frequency of said source; said series resonant circuit having a Q greater than unity; circuit means, having an impedance which varies in response to changes in ambient light intensity, connected in parallel circuit with one of said resonant elements for controllably modifying said Q value; said relay being effective to transfer said A-C power from the source to the load upon the condition of a predetermined voltage across said coil; said transfer being preselected to occur at a condition of saturation of said magnetic path whereby the inductive reactance of said coil may be controllably modified to maintain said predetermined voltage relatively invariant with changes in supply voltage over a predetermined range.

6. The combination according to claim 5 wherein said circuit means is a photo-conductive cell.

7. A control circuit for transferring power from an A-C source to a load, said control circuit adapted for uniform operation over a range of line voltages from approximately volts to 275 volts supplied by said source, said control circuit comprising a voltage-operated relay, said relay having a coil, a saturable magnetic flux path, and at least one pair of contacts; a capacitive reactance connected in series circuit with said relay coil across said source to form a series resonant circuit at the A-C frequency of said source; said pair of contacts connected between said source and said load, and adapted to transfer power therebetween upon operation of said relay as defined by a predetermined voltage level across said relay coil; said relay having a rst preselected operating point, at which said series circuit is in resonance and said magnetic path is saturated, at the lowest of said source voltages; said series circuit having a Q of greater than unity; said relay having a second preselected operating point at the highest of said source voltages, at which said magnetic path is further saturated whereby the inductive reactance of said relay coil is reduced in value and said series circuit is detuned; said reduced coil reactance being effective to maintain said coil voltage at substantially said predetermined level at said lowest and said highest source voltages and in the range therebetween; and variable impedance means shunting one of said capacitive reactance and said relay coil for controllably reducing said Q.

8. The combination according to claim 7 wherein said variable impedance means is a photo-conductive cell.

References Cited UNITED STATES PATENTS 4/1961 Mitchell et al. 317-125 X 3/1963 Howell 307-117

Claims (1)

1. A CONTROL CIRCUIT FOR CONNECTING AN A-C POWER SUPPLY LINE TO A LOAD, SAID CONTROL CIRCUIT ADAPTED FOR UNIFORM OPERATION OVER A RELATIVELY WIDE RANGE OF LINE VOLTAGES, COMPRISING, IN COMBINATION, A RELAY HAVING AN INDUCTION COIL AND A SATURABLE MAGNETIC PATH, A CAPACITOR CONNECTED IN SERIES CIRCUIT WITH SAID COIL TO FORM A RESONANT CIRCUIT ACROSS THE SUPPLY LINE, AN ACTIVATING ELEMENT HAVING AN IMPEDANCE WHICH VARIES IN RESPONSE TO CHANGES IN AMBIENT LIGHT INTENSITY, MEANS CONNECTING SAID ACTIVATING ELEMENT IN PARALLEL CIRCUIT WITH ONE OF SAID RESONANT ELEMENTS SO THAT SAID ACTIVATING ELEMENT CONTROLS THE CURRENT PASSING THROUGH SAID COIL TO MODIFY THE Q OF SAID RESONANT CIRCUIT WHEN THE AMBIENT LIGHT INTENSITY ON THE ACTIVATING ELEMENT CHANGES, SAID RELAY INCLUDING MEANS EFFECTIVE TO CONNECT SAID LINE TO SAID LOAD UPON THE CONDITION OF A PREDETERMINED VOLTAGE ACROSS SAID RELAY COIL, SAID RELAY HAVING PRESELECTED OPERATING POINTS SOLELY IN THE CONDITION OF SATURATION OF THE RELAY MAGNETIC FLUX PATH WHEREBY THE OPERATING VOLTAGE ACROSS SAID RELAY COIL IS MAINTAINED SUBSTANTIALLY INVARIANT OVER SAID RELATIVELY WIDE RANGE OF LINE VOLTAGES.

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