US2167227A - Relay circuit - Google Patents

Description

y 1939 J. M. WILSON- 2,167,227

RELAY CIRCUIT Filed June 2, 1958 CONTACTS OVERLAPPING ON TEMPERATURE RISE ONLY w Fmg 2 Fig 11 Snventdr Jollmn MaWillson I BE attorney Patented July 25, 1939 PATENT OFFICE RELAY CIRCUIT John M. Wilson, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., ware a corporation of Dela- Application June 2, 1938, Serial No. 211,402

Claims.

The present invention relates to a relay circuit and more particularly to one wherein provision is made for the relay moving to its deenergized position upon a relatively small reduction in voltage.

In certain types of control systems, it is highly desirable to have the relay drop out upon the voltage of the source of power decreasing a relatively small amount below the value at which the relay is pulled in. In the case of an oil burner" control system having electrical ignition means, for example, a reduction in voltage during operation of the burner may cause the ignition means to become deenergized and yet still permit the motor to run. This is true inasmuch as in many systems, the ignition means requires a much higher voltage forjoperation than do the motors of the systems. If the motor continues to run, oil will be supplied to the furnace, this oil being unignited. While means are usually provided for eventually deenergizing the system in the event of combustion failure, such means requires an appreciable time for operation. If it is assured that the voltage is not sufficiently high to operate the ignition, there is no need to delay the deenergization of the system for this period of time since it is assured that the burner will not again be placed in operation. It can readily be seen from the foregoing that it is highly desirable that the relay controlling the oil burner and ignition circuits be of a type which moves to its deenergized position upon a relatively small drop in voltage. It has been proposed in the past to connect a resistance in series with the relay coil upon energization of the relay, this resistance serving to reduce the voltage applied to the relay coil and hence to make it possible for the relay to drop out upon a relatively small reduction in line voltage. The disadvantage of such a resistance is that at the time that the resistance is connected in the circuit, the power factor is changed. This change in power factor may so disturb the flux flow in the core structure of therelay that the relay drops out momentarily. Where, as it is desirable in the case of certain systems, the original energizing circuit is interrupted at the moment the impedance is connectedin series with the relay coil, this dropping out of the relay instead of being momentary 50- will be. permanent, since the impedance is of such value that the relay cannot initially pull in with the impedance connected in series therewith. q An object of the present invention is to provide a,circuit arrangement for an electromagnetically operated device biased to one position in which an impedance having the same power factor as the electromagnetic operator is connected in series therewith upon energization of the operator.

A further object of the invention is to provide a relay circuit in which an impedance having the same power factor as the relay is connected in series therewith upon energization of the relay.

.A further object is to provide such a relay circuit in which the relay controls a condition producing device and in which the connection of the impedance is dependent both upon one of the relay switches and upon a switch responsive to the condition produced by operation of said device.

A further object of the invention is to provide a relay circuit according to the previous object in which the condition responsive switch is effective to break the original energizing circuit to the relay as soon as the circuit including the impedance has been established.

Other objects of the invention will be apparent from a consideration of the accompanying specification, claims and drawing, of which:

Figure 1 is a schematic view of an oil burner circuit including the novel relay circuit oi? the present invention, and

Figure 2 is a slightly modified form of the relay circuit.

As indicated above, Figure 1 is a schematic view of an oil burner control circuit incorporating the improved relay circuit. The oil burner is generally designated by the reference numeral I0 and comprises the usual nozzle II and the usual blower driven by a motor l2. The blower is effective to force an atomized mixture of fuel through the nozzle ll. provided for the purpose of igniting the fuel issuing from the nozzle. This ignition means may be of any conventional type such as a high voltage transformer connected to suitably spaced spark electrodes.

The energization of the oil burner and ignition means is controlled by a relay generally designated by the reference numeral l6. This relay comprises a coil I1 which is operatively associated'with an armature l8 connected to switch blades I9, 20, and 2t. Switch blades 69, 26, and 2| are biased to the right by any suitable means (not shown), but are adapted to bemoved, upon energization of the relay coil. i'i into engagement with contacts 23, 2d, and 25, respectively.

An ignition means I4 is While the relay has been shown schematically as of a type comprising a solenoid coil through which a core is movable, it is to be understood that the relay can be of any conventional electromagnetic type wherein the reluctance of the magnetic circuit is decreased upon the armature moving'to its energized position.

The energization of the relay I6 is controlled by a room thermostat 28. This room thermostat comprises a bimetallic element 21 to which is secured a composite contact arm 29. The contact arm 29 is adapted to sequentially engage contacts 38 and 3i. Upon a temperature fall, the contact arm 29 is adapted to first engage contact and then to engage contact 3|.

Also controlling the energization of relay I1 is a thermal safety switch 35. This safety switch may be of the form shown in the patent to F. S. Denison No. 1,958,081, issued May 8, 1934. As shown in the drawing schematically, the switch comprises two switch blades 36 and 31, the lower one of which is pivotally mounted. The bimetallic element 38 when in its cold position extends under switch blade 31 and holds the same in contact making position with switch blade 36. A heater 39 is located adjacent the bimetallic element 38 and serves when energized to heat the element 38 causing the latter to warp to the right. It will be obvious that if this heating is continued sufiiciently long, bimetallic element 38 will be warped to the right sufficiently to permit switch blade 31 to drop away from switch blade 36.

A stack switch generally indicated by the reference numeral 48 is provided for the purpose of indicating when combustion has taken place. This switch comprises a temperature responsive element (not shown) which actuates a switch blade 4| through a slip friction connection. The switch blade 4| when in its cold position, engages a contact 42. Upon the temperature responsive element of switch 48 being subjected to a rise in stack temperature, the switch blade 4| is moved into engagement with a contact 43. The assembly consisting of switch blade 4| and contacts 42 and 43,is so designed that switch 3 blade 4| moves into engagement with contact 43 before it moves out of engagement with contact 42. Upon a temperature fall, switch blade 4| moves out of engagement with contact 43 before it moves into engagement with contact 42. In other words, the contacts are overlapping on temperature rise but non-overlapping on temperature fall. The switch 48 may take the form of the switch disclosed in the patent to A. F. Erickson No. 1,969,974, issued January 2, 1934.

A choke coil is designated by the reference numeral 45. This choke coil is so designed as to have the same power factor as the relay coil |1 when the armature of the relay is in its energized position. This choke coil comprises the usual winding 46' and core 41 of magnetic material.

The step-down transformer 58 is provided for the purpose of supplying low voltage power for operation of the control portion of the system. This transformer comprises a line voltage primary 5| and a low voltage secondary 52. The primary 5| is connected to line wires 53 and 54 leading to any suitable source of power (not shown).

s'fperation of Figure 1 species The elements are shown in the system in the position they occupy when the temperature to which thermostat 28 is responsive is at or above the desired value. Upona drop in temperature,

the contact arm 29 first engages contact 38 and then contact 3|. The engagement of arm 29 with contact 38 has no effect. As soon as it engages contact 3|, however, an energizing circuit is established to relay coil H as follows: from the right-hand terminal of secondary 52 through conductor 56, contact- 38, contact arm 29, contact 3|, conductors 51 and 58, heating element 39, conductor 59, contact 42, contact blade 4|, conductor 68, relay coil l1, conductor 6|, switch blades 31 and 36, and conductor 62 to the other terminal of secondary 52. The establishment of this circuit causes the energization of relay coil |1 so that switch blades I9, 28, and 2| are moved into engagement with contacts 23, 24, and 25, respectively.

The moving of switch blade 28 into engagement with contact 24 results in the establishment of the following holding circuit to relay coil l1: from the right-hand terminal of secondary 52 through conductor 56, contact 38, contact arm 29, bimetallic element 21, conductors 63 and '64, contact 24, switch blade 28, conduc-,

tors 65 and 58, heating element 39, conductor 59, contact 42, switch blade 4|, conductor 68, relay coil |1, conductor 6|, switch blades 31 and 36, and conductor 62 to the other terminal of secondary 52. It will be noted that the circuit just traced is independent of contact 3|. It is now possible for the contact blade 29 to move away from contact 3| without interrupting the energization of the relay coil. The relay coil thus does not become deenergized until contact arm 29 disengages contact 38. It will thus be seen that a differential is required between energization and deenergization of the relay |6, thus eliminating any danger of excessively frequent energization and deenergization of the control apparatus by reason of a chattering of the thermostat contacts.

The moving of relay switch blade 2| into engagement with contact 25 results in the establishment of the following energizing circuit to the oil burner motor l2: from line wire 53, through conductor 66, contact 25, switch blade 2|, conductors 61 and 68, burner motor l2, and conductor 69 to the other line wire 54. At the same time the following circuit is established to the ignition means l4: from line wire 53 through conductor 66, contact 25,v switch blade 2|, conductors 61 and 1|, ignition means I 4, and conductors 12 and 69 to the other line wire 54. The establishment of these two circuits to the oil burner motor and to the ignition means results in the establishment of the conditions necessary for combustion.

It will be noted that the two circuits traced to relay coil |1 included heating element 39. If combustion does not take place within a predetermined period of time after the ignition of the oil burner motor and the ignition means l4, the heating element 39 will heat the bimetallic element 38 sufliciently that it will permit switch blade 31 to drop away from switch blade 36. When this happens, the complete system is deenergized and cannot be reenergized until the safety switch 35 is manually reclosed by the operator.

If combustion does take place upon energiza- ,tion of the oil burner m or and the ignition means l4, as will usually be the case, the temperature of the stack will very quickly rise so as to cause switch blade 4| to move first into engagement with contact 43 and immediately thereafter out of engagement with contact 42.

As soon as switch blade 4| engages contact 43, a new circuit is established to the relay coil I! as follows: from the right-hand terminal of secondary 52 through conductor 56, contact 38, contact arm 29, bimetallic element 21, conductors 63 and 13, contact 23, switch blade I9, conductor I4, choke coil 45, conductor I5, contact 43, switch blade 4|, conductor 68, relay coil I1, conductor 6|, switch blades 31 and 36, and conductor 62 to the other treminal of relay coil 52. It will be noted that this new circuit includes the choke coil 45. Until the switch blade 4| disengages contact 42, however, the choke coil 45 is effectively shunted out of the circuit since the resistance of heater 39 is relatively small. As soon as switch blade 4| leaves contact 42, this shunt circuit through heater 39 is interrupted and all of the current to relay coil I! must pass through the choke coil 45. It will be seen that the stack switch 48 has had two effects. In the first place, it has connected the choke coil 45 in series with relay I! to thereby reduce the drop in voltage necessary to cause the relay to move to its deenergized position. In the second place, the heating coil 39 has been deenergized to thereby render the safety switch 35 inoperative to interrupt operation of the system. This deenergization of the heating element 39 is desirable since it is now assured that combustion has been established.

By reason of the fact that the choke coil 45 has the same power factor as the relay coil N, there will be no disturbance in the power factor of the circuit when the choke coil isconnected in series with the relay coil. It is true that the resistance of heating element 39 is removed from the circuit but this resistance is so slight that it does not appreciably affect the power factor of the circuit. Since the power factor of the circuit is not changed, the relay coil I! will not drop out, even momentarily.

It is further to be noted that the circuit for the relay coil I'I including the choke coil 45 is dependent upon the closure of the switch blade I9 with contact 23. Thus if the voltage should drop, causing the relay IE to move to its deenergized position, the relay could not again be reenergized until the stack temperature had cooled down sufliciently to remake switch blade 4| with contact 42 to reestablish the original energizing circuit for the relay. If some such means as this were not provided, the relay might drop out upon the choke coil being connected in series therewith merely as a result of the heavy load placed on the line by both the oil burner motor and ignition means, and then would immediately pull in again as soon as the oil burner and ignition was disconnected by reason of the relay dropping out. The relay would thus cycle back and forth between its energized and deenergized positions. With the present arrangement, it is assured that when the relay drops out, it must stay out until the stack has cooled down sulficiently to reengage switch blade 4| with contact 42.

With the choke coil 45 connected in series with relay coil I1, any appreciable drop in voltage will be effective to cause an immediate movement of relay I6 to its deenergized position. As soon as the relay moves from its energized position, the energizing circuit thereto is completely broken and the system is not restarted until both the voltage is restored to normal and the stack switch has moved back to its cold position. If the stack switch moves back to its cold position and the voltage is still too low, the heating element 39 will eventually heat up and cause safety switch 35 to deenergize the system.

If flame failure occurs for any reason during operation of the system, the cooling of the stack temperature will cause switch blade 4| to reengage contact 42. Relay I'I will once more be energized, if .contact blade 29 is still in engagement with contact 3| whereupon the entire cycle will be repeated. Thus upon flame failure during operation, it is possible to again automatically restart the burner if conditions are proper. If not, the safety switch 35 is opened just as during the normal starting period.

Species of Figure 2 In certain types of systems, it will be desirable to have the choke coil connected in series with the relay coil immediately upon energization of the relay coil. Such a relay circuit is shown in Figure 2. In this figure, the relay is designated by the reference numeral 88 and comprises a relay coil 8| which has associated therewith a movable armature 82 adapted to position switch blades 83 and 84. The switch blades 83 and 84 are biased to the right, switch blade 83 being biased into engagement with a contact 85. Switch blade 84 is adapted to be moved into engagement with a contact 86. Upon energization of the relay coil 8|, switch blade 83 is moved out of engagement with contact 85 and switch blade 84 into engagement with contact 86. The switch blade 84 and contact 86 may be used to control any suitable load circuit. A thermostat 8! is shown as controlling the energization of the relay 88. This thermostat comprises a bimetallic element 88 and a contact arm 89 secured thereto. The contact arm 89 is adapted to move into engagement with a fixed contact 98 upon a suflicient temperature drop. A magnet 9| is associated with the contact arm 89 to impart a snap action thereto.

A step-down transformer is generally indicated by the reference numeral 93. This transformer comprises a line voltage primary 84 and a low voltage secondary 95. This transformer corresponds to the transformer 58 of the species of Figure 1. A choke coil 96 corresponds to the choke coil This choke coil, like choke coil 45, comprises a winding 91 and a magnetic core 98.

When the temperature to which thermostat 81 is subjected drops to a predetermined point, contact arm 89 is moved into engagement with contact 98 with a snap action. Upon this occurring, the relay coil 8| is energized through the following circuit: from the right-hand terminal of secondary 95 through conductor I88, contact 98, contact arm 89, bimetallic element 88, conductors I8| and I82, switch blade 83, contact 85, conductor I83, relay coil 8 I and conductor I84 to the other terminal of secondary 95.. In addition to the energizing circuit just mentioned, there is also a circuit established to relay coil 8| as follows: from the right-hand terminal of secondary 95 through conductor I88, contact 98, contact arm 89, bimetallic element 88, conductors I8I and I86, choke coil 96, conductor I81, relay coil 8|, and conductor I84 to the other terminal of secondary 95. Inasmuch as the choke coil 96 is effectively shunted by conductor I82, switch blade 83, contact 85, and conductor I83, this second circuit will play no particular part in the energization of relay coil 8| so long as switch blade 83 is in engagement with contact 85. Upon energization of the relay coil 8|, however, switch blade 83 is moved out of engagement with contact 85, thus interrupting the shunt around choke coil 96 so that choke coil 96 is now effectively connected in series with relay coil M.

The connection of choke coil 96 in series with relay coil 8| has the same effect as the connection of choke coil 45 in series with the relay in the species of Figure 1. In other words, upon any appreciabledrop in the supply voltage, the relay 8!] moves to its deenergized position. As in the preferred species, the power factor of the choke coil 96 is the same as that of the relay 8| when the armature is in its energized position. Thus, the connection of the choke coil 96 in series with the relay 8| does not disturb even momentarily the power factor of the entire relay circuit.

It will be seen that I have provided a new and I novel relay circuit in which the drop-out voltage of the relay is increased without disturbing the power factor of the relay circuit. While I have disclosed a specific embodiment of my invention for piu'poses of illustration, it is to be understood that the invention is to be limited only by the scope of the appended claims.

I claim as my invention:

In combination, a device biased to one positionand including an electromagnetic operator for moving it to another position, an alternating current source of power for energizing said electromagnetic operator, a constant impedance having the same power factor as said operator when said device is in said other position, and means operative subsequent to the energization of said operator to connect said impedance in series with said operator so as to reduce the drop in voltage necessary to cause said device to return to its biased position.

2. In combination, an electromagnetic relay, an alternating current source of power for energizing said relay, a constant impedance having the same power factor as said relay when in its energized position, and means operative subsequent to the energization of said relay to connect said impedance in series with said relay.

3. In combination, an electromagnetic relay biased to one position and adapted upon energization to move to a second position, an alternating current source of power for energizing said relay, a constant impedance having the same power factor as said relay when in said second position, and means operative subsequent to the energization of said relay to connect said impedance in series with said relay so as to reduce the drop in voltage necessary to cause said relay to return to its biased position.

4. In combination, a device biased to one position and including an electromagnetic operator for moving it to another position, an alternating current source of power for energizing said electromagnetic operator, a constant impedance choke coil having the same power factor as said operator when said device is in said other position, and means operative subsequent to the energization of said operator to connect said choke coil in series with said operator so as to reduce the drop in voltage necessary to cause said device to return to its biased position.

5. In combination, an electromagnetic relay, an alternating current source of power for energizing said relay, a constant impedance choke coil having the same power factor as said relay when in its energized position, and means operative subsequent to the energization of said relay to connect said choke coil in series with said relay.

6. In combination, an electrically operated condition producing device, a relay comprising an; electromagnetic coil and a plurality of switches actuated thereby, one ofsaid switches controlling the energization of said device, a switch controlling the energization of said coll, a constant impedance having the same power factor as said relay coil when said switches are in their energized position, and means dependent upon both the movement of one of said relay switches to its energized position and the'establishment of the condition produced by energization of said device for connecting said impedance in series with said coil.

7. In combination, an electrically operated condition producing device, a relay comprising an electromagnetic coil and a plurality of switches actuated thereby, one of said switches controlling the energiz-ation of said device, a switch controlling the energizationn of said coil, a constant impedance having the same power factor as said relay coil when said switches are in their energized position, and means dependent upon both the movement of one of said relay switches to its energized position and the establishment of the condition produced by energization of said device for establishing a new energizing circuit for the relay coil including said impedance and for interrupting the initial energizing circuit for the coil.

8. In combination, a device biased to one position and including an electromagnetic operator for moving it to another position, an alternating current source of power for energizing said electromagnetic operator, a constant impedance having the same power factor as said operator when said device is in said other position, said impedance being connected in series with said operator, means for normally shunting said impedance, and means operative subsequent to the energization of said operator to interrupt said shunting means.

9. In combination, an electromagnetic relay, an alternating current source of power for energizing said relay, a constant impedance having the same power factor as said relay when energized and connected in series therewith, means for normally shunting said impedance, and means operative subsequent to the energization of said operator to interrupt said shunting means.

10. In combination, an electromagnetic relay biased to one position and adapted upon energization to move to a second position, an alternating current source of power for energizing said relay, a constant impedance having the same power factor as said relay when energized and connected in series therewith, means for normally shunting said impedance, and means operative subsequent to the energization of said operator to interrupt said shunting means and thereby reduce the drop in voltage necessary to cause said relay to return to its biased position.

JOHN M. WILSON.

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