US2086823A - Control system for fuel burners - Google Patents

Description

July 13, 1937. B. E. SHAW 2,086,823

CONTROL SYSTEM FOR FUEL BURNERS Filed Aug. 3, 1936 2 Sheets-Sheet 1 lst 24 3O lst 24 26 32 3 CS 2nd 26 2a /2nd 28 July 13, 1937. Y B. E. SHAW 2,086,823

CONTROL SYSTEM FOR FUEL BURNERS Filed Aug. 5, 1956 2 Sheets-Sheet 2 Patented July 13, 1937 UNITED STATES CONTROL SYSTEM FOR FUEL BURNERS Burton E. Shaw, Adel,

Iowa, assignor to Penn Electric Switch 00., Des Moines, Iowa, a corporation of Iowa I Application August 3,

16 Claims.

One object of my present invention is to provide a control system involving a simple and inexpensive arrangement of elements for controlling a fuel supply motor and ignition means for the fuel supplied by the motor. A further object is to provide a control system in which a safety switch is operable if combustion does not occur or if it fails after occurrence to render the system inoperable, a combustion switch being provided with substitutes a resistance for the safety switch heater upon successful establishment of combustion, thereby maintaining substantially the same current value in the control circuit in either position of the combustion switch.

Still another object is to provide a control circuit for a control system of the character disclosed, which includes a pair of resistances and a safety switch heater, a combustion switch being operable to permit one of the resistances and the safety switch heater to remain energized if combustion is not established, and operable to substitute the other resistance for the safety switch heater if combustion is successfully established.

Still a further object is to provide a control system including a control circuit having one resistance therein provided for the purpose of preventing a dead short on the secondary of a transformer which supplies current to the control circuit in an intermediate position of a combustion switch.

Still a further object is to provide such a system so wired and having elements so related that low voltage protection is secured, a single relay or, the like being operable to cut in at one value of the voltage and to cut out at a point only a few volts below the cut-in voltage.

Still a further object is to provide a control system which can be arranged by including an electro-responsive ignition trip switch and additional combustion switch contacts, whereby intermittent instead of continuous ignition may be provided for.

A further object is to provide a modified form of control system in which a safety switch is operable if combustion does not occur or if it fails after occurrence to render the system inoperable, a combustion switch being provided which rendersthe safety switch heater inoperable upon successful establishment of combustion.

Another object is to provide in said modified form, a transformer so connected with a relay, a safety switch heater and a resistance that after the relay is energized, a safety switch heater circuit is established having only the resistance and the safety switch heater therein, while after combustion establishment, only the resistance remains in circuit to prevent a short circuit affect- 1936, Serial No. 94,046 (01. 158-28) ance and the safety switch heater to remain energized if combustion is not established, and operable to permit the resistance only to be energized if combustion is successfully established.

Still afurther object is to provide in. said 1 modified form a control system including a control circuit having a resistance therein provided for the. purpose of preventing a dead short on the secondary of a transformer which supplies current to the control circuit in the hot stack position of a combustion switch.

With these and other objects in view, my invention consists in the construction, arrangement and combination of the various parts of the device, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawings, in which:

Figure 1 is an electrodiagrammatical view of a burner control system embodying my invention arranged and wired for continuous ignition, showing the combustion switch thereof in cold stack position.

Figure 2 is a view of the combustion switch of Figure l in an intermediate position.

Figure 3 is a similar view showing the combustion switch in hot stack position.

Figure 4 is an electrodiagrammatical view similar to Figure 1 but arranged and wired for intermittent instead of continuous ignition.

Figures 5 and 6 are views of the combustion switch of Figure 4 showing it in a first and second intermediate position.

Figure 7 is a similar view showing the combustion switch in hot stack position.

Figure 8 is a view of the ignition trip switch in Figure 4, showing it in position breaking the ignition circuit.

Figure 9 is a view similar to the upper portion of Figure 4 and showing a modified form of control system.

0n the accompanying drawings inFigures 1 to 8 I have used the reference character M to indicate a fuel supply motor. This is the usual blower motor provided in connection with a burner for supplying oil, gas or other fuel, together with the proper amount of air to the burner nozzle. Ign indicates the ignition mechanism for the fuel supplied to the burner by the motor M. The motor M and the ignition mechanism Ign are controlled as to energization by a motor switch MS, and as to deenergization due to improper operation of the burner by a safety switch SS, current being supplied to the motor and the ignition mechanism from a suitable source indicated on the drawings as current supply.

A transformer T is provided, the primary of which is indicated at l0 and the secondary thereof at I2. This is a step-down transformer so that low voltage current can be supplied for a control circuit controlled by a temperature responsive control switch such as a room thermostat RT.

The control circuit includes a relay coil RC, three resistances R, SSH and R (the resistance SSH being a safety switch heater) and a holding switch HS. The relay coil is part of a relay, the core of which is indicated at l4 and the armature thereof at l 6. The armature is normally retained in the position illustrated in Figure 1 by a spring l8. The armature I6 is operatively connected with the motor switch MS and the holding switch HS for closing them upon energization of the relay coil RC.

A bimetal element 20 is arranged adjacent the safety switch heater SSH and warps upwardly to a position permitting a leaf spring or the like 22 to return to its normal position after the safety switch heater has been energized for a predetermined period of time. The spring 22, when finally assuming its normal position, separates the contacts of the safety switch SS. The safety switch, the elements 20 and 22 and the safety switch heater constitute a thermal time limit cut-out switch controlling the system so as to render it inoperable if combustion does not occur, or if it fails after it has been established. 1

A combustion switch CS is provided having contact springs 24, 2B and 28 suitably mounted on blocks 30 of insulation or the like. The spring 26 is so extended that it contacts with the periphery of a notched disk 32. This disk is actuated to rotate in a clockwise direction, due to an increase in the temperature in the combustion chamber of a furnace in which the burner, operated by the motor M, is located, and to rotate in an opposite direction upon failure of combustion.

Upon rotation of the notched disk in a clockwise direction, due to combustion establishment, the spring 26 will be flexed downwardly from the position of Figure 1 to the position of Figure 2, wherein contacts carried by the springs 24, 26 and 28, (and indicated as lst and 2nd.) of the combustion switch CS will all be engaged as their contact action overlaps. Further clockwise rotation of the notched disk 32 will separate the lst contacts and maintain the 2nd ones engaged, while further clockwise rotation of the notched disk 32 may occur without changing the position of the combustion switch. Likewise, during counter-clockwise rotation of the notched disk 32, when combustion has failed and the lst and 2nd contacts assume the position of Figure 1, the disk will have no further effect on the position of the contacts.

It is believed that the operation of the combustion switch CS is obvious from the foregoing description, although its complete construction and operation are explained in the Williams Patent No. 1,827,703 of October 13, 1931.

The holding switch HS is connected with a center tap of the secondary l2 of the transformer T, and with the control circuit at a point between the relay coil RC and the resistance R. The purpose and operation of this switch will be hereinafter explained.

In the circuit of Figure 1, continuous ignition is provided, as the ignition Ign is controlled only by the motor switch MS being both energized and deenergized thereby. To obtain intermittent ignition, an ignition circuit breaker or ignition trip switch ITS (see Figure 4) is provided, which is cut into the circuit between the motor switch and the ignition mechanism. It is operable by the relay coil in conjunction with a latch 34, an armature 36 operatively connected therewith and a trip coil TC.

The trip coil TC is controlled by 3rd and 4th contacts of the combustion switch CS, which are provided in addition to the lst and 2nd ones of Figure 1.

The combustion switch of Figure 4 has the leaf springs 24, 26 and 28, the spring 26 carrying one 7 of the contacts of the 3rd set of contacts of the combustion switch. A leaf spring 26a is provided which contacts with the periphery of the notched disk 32. A fifth spring 38 is provided carrying one of the contacts of the 4th set of contacts of the combustion switch. The spring 28a carries the other contacts of the 3rd and 4th sets of combustion switch contacts.

The ignition trip switch ITS is illustrated as comprising a pair of leaf springs 43 and 42 anchored to a block 44 of insulation. The leaf spring 42 has an extension 15 for cooperation with the latch 34.

For purposes of illustration, the oper ve connection between the armature IS, the holding switch HS, the motor switch MS and the ignition trip switch ITS is shown diagrammatically at 48 as a broken line, terminating in an end 58 adapted when the relay coil RC is (fie-energized to en-- gage the leaf spring 42 and close the contacts of n the ignition trip switch, as shown in Figure 4. The operative connection between the leaf spring 22 of the safety switch heater and the safety switch is likewise illustrated at 52 as a broken With reference to the modified form shown in Figure 9, a circuit is illustrated which omits the resistance R of Figures 1 to 8. This control circuit includes only two resistances, R and SSH and the combustion switch omits the leaf spring 24 of Figures 1 to 8. Accordingly the contacts are designated .Ist, 2nd and 3rd instead of 2nd, 3rd and 4th as in Figures 1 to 8.

PRACTICAL OPERATION FOE Fro-Units 1 To 8 Starting circuit In the operation of my control system, a starting circuit is established when the room thermostat calls for heat. Upon closure of the room thermostat, a secondary or'control circuit is traceable through the following wires (lower case letters being used to designate the wires) and elements of either Figure l or Figure 4: a, RT, b, RC, 0, d, 24,,lst, 2B, SSH, R and e.

The current supply for the starting circuit as thus traced is the entire output of the secondary l2. Energization of the relay coil attracts the armature I6, so that the motor switch is closed, thereby energizing the ignition mechanism and the burner motor for initiating operation of the burner. The armature l6 also closes the. holding switch HS so that thereafter there are two circuits supplied with current from the secondary l2.

Holding circuit One of these circuits is a holding circuit traceable through the following wires and elements: a, RT, 22, RC, 1, HS and g. It is now obvious that the. relay coil is being maintained energized by iii vturns from the position of Figure 3 through the only half of the secondary l2. When the wire a is tapped to the transformer exactly half way between the terminals thereof, by having the impedance of RC greater than the sum of the impedances of R and SSH, this current is weaker than the initial current from the entire secondary l2. Therefore, the gaps in the relay switches HS and MS can be quite wide and yet the relay will cut out upon only a substantially small drop in the normal line voltage. This gives low voltage protection which is a very desirable feature as fully set forth in my co-pending application Serial Number 52,595, filed December 2, 1935. The other of these two circuits is a Safety switch heater circuit When the holding switch is closed, the upper half of the secondary l-2 becomes operative as the means for supplying current to the safety switch heater. This constitutes a safety switch heater circuit traceable through the following wiresand elements: g, HS, 1, c, d, 24, lst, 26, h, SSH, R and e. If combustion does not occur in a predetermined period of time, the heat generated in the safety switch heater, due to the current flowing through the safety switch heater circuit, opens the safety switch SS, thus de-energizing the entire system. The cause for combustion failure must then be remedied by the service man, and the spring 22 manually swung to the left so that the bimetal element 29 (then cool) will latch it in such position.

Running circuit If combustion occurs, the notched disk 32 will first assume the position of Figure 2, whereupon instead of the safety switch heater circuit above traced, the circuit will then be traceable through the following wires and elements: g, HS, f, c, d, 24, lst, 2nd, 28, i, R and e. Both the resistance R and the safety switch heater SSH are shunted out of the circuit during this period of time. The resistance R, however, when the parts are in the position of Figure 2, prevents a dead short circuit across the upper half of the secondary l2, which would have the effect of weakening the current in the lower half of the secondary, and

consequently in the relay coil RC, so that if the line voltage were somewhat low, yet not undesirably low, the relay might drop out.

As the stack heats up, the disk 32 will assume the position of Figure 3, wherein the first contacts of the combustion switch are opened and thereupon the safety switch heater circuit is no longer in operation. Instead, a running circuit is established traceable through the following wires and elements: a, HS, f, c, R, h, 26, 2nd, 28, i, R and e. The combustion switch has in effect substituted the resistance R for the resistance heater SSH, so that the safety switch heater is no longer operative to warp the bimetal latch 20 upwardly. The. resistance R is now in series with the resistance R. The total resistance value of these two resistances is approximately the same 'as the total resistance value of the resistance R and the safety switch heater in series. Thus in either the cold stack or hot stack position of the combustion switch, the load on the upper half of the secondary I2 is substantially the same, soas not to vary the available current for maintaining the relay coil energized.

Combustion failure after combustion has been established position of Figure 2 to the position of Figure 1. When in the position of Figure 1, the safety switch heater circuit is again established, where-- by after a predetermined period of time, the safety switch is opened, thus providing protection for the system against combustion failure due to any cause.

Intermittent ignition control With the circuit of Figure 4, in addition to the foregoing description of the practical operation of my control system, the ignition mechanism Ign is de'energized upon combustion being established. Deenergization occurs when the combustion switch reaches the position illustrated in Figure 5. In this position, the 3rd contacts of the combustion switch have engaged, thereupon establishing a trip coil circuit through the following wires and elements: w, RT,-7', the trip coil TC, is, 38, 4th, 3rd, 26, lst, 24, d, c, 1, HS, and g.

Energization of the trip coil causes the armature 36 to be attracted, thereby raising the latch 34. The armature I6 has been attracted by the relay coil RC, so that the terminal end of the operative connection 48 is in the position of Figure 8. This permits the leaf springs 40 and 42 to return from the position of Figure 4, in which they are held by the terminal end 50, when the relay coil RC is de-energized, to the position of Figure 8 when the latch 34 is raised by the armature 36. This breaks the ignition circuit which was established by the motor switch MS when it closed as a result of energization of the relay coil. Further movement of the combustion switch to the position of Figure 6 separates the 4th contacts of the combustion switch, thereby de-energizing the trip coil TC, as after it has raised the latch 34, there is no further need for its energization. In this position both the lst and 2nd contacts are closed as in Figure 2, while upon further movement of the combustion switch toward hot stack position, the lst contacts are separated as shown in Figure 7, which corresponds to the position shown in Figure 3.

Consequently, when the room thermostat opens or when the relay coil is tie-energized from any other cause, the spring l8 returns the armature Hi to the position shown in Figure 4, whereupon the terminal end 50 of the operative connection 48 closes the ignition trip switch, thus resetting it for the next operation, although the ignition mechanism is not energized because the motor switch MS is open.

In the event of power failure, the burner can start up immediately following resumption of power. Power failure results in the de-energization of the transformer T and consequently deenergizes the relay coil RC so that the motor switch MS is thereby opened. Regardless of the position of the combustion switch CS, a starting circuit can be established across the entire secondary l2, as in any position of the stack switch, current can flow from the wire 0 to the wire e, although in some positions, the resistance value between these two Wires is different.

As soon as the starting circuit has been established then, of course, the holding switch is closed, resulting in the lower half of the secondary l2 supplying current for the relay coil and the upper half supplying current for the safety switch heater when the combustion switch is in position permitting passage of the current therethrough.

Referring to Figure 1, whenever the power has circuit is no longer failed and is again resumed, such starting up of the burner will be with ignition, because the ignition is controlled by the motor switch. Similarly in Figure 4, the motor switch will also energize the ignition, because upon power failure, the ignition trip switch, which was open because combustion had been established, is reclosed by the relay armature l6 returning to its initial position. It is therefore impossible for the burner to start up without ignition and cause an explosion.

PRACTICAL OPERATION ron FIGURE 9 Starting circuit my modified form of control system, a starting circuit is established when the room thermostat calls for heat. Upon closure of the room thermostat, a secondary or control circuit is traceable through the following wires (lower case letters being used to designate the wires) and elements of Figure 9 taken in conjunction with Figure 4: a, RT, b, RC, c, SSH, R and e.

The current supply for the starting circuit as thus traced is the entire output of the secondary l2. Energization of the relay coil attracts the armature [6, so that the motor switch is closed, thereby energizing the ignition mechanism and the burner motor for initiating operation of the burner. The armature switch HS so that thereafter there are two circuits supplied with current from the secondary l2.

In the operation of Holding circuit One of these circuits is a holding circuit traceable through the following wires and elements: a, RT, b, RC, f, HS and g. It is now obvious that the relay coil is being maintained energized by only half of the secondary l2. When the wire 9! is tapped to the transformer secondary exactly half way between the terminals thereof, by hav ing the impedance of RC greater than the sum of the impedances of R and SSH, this current is weaker than the initial current from the entire secondary I2. Therefore the gaps in the relay switches HS and MS can be quite wide and yet the relay will cut out upon only a substantially small drop in the normal line voltage to give low voltage protection. The other of these two circuits is a Safety switch heater circuit When the holding switch is closed, the upper half of the secondary I2 becomes operative as the means for supplying current to the safety switch heater. This constitutes a safety switch heater circuit traceable through the following wires and elements: 9, HS, f, c, SSH, R and e. If combustion does not occur in a predetermined period of time, the heat generated in the safety switch heater, due to the current flowing through the safety switch heater circuit,- opens the safety switch SS, thus de-energizing the entire system. The cause for combustion failure must then be remedied by the service man, and the spring 22 manually swung to the left so that the bimetal element (then cool) will latch it in such position.

Running circuit If combustion occurs, the notched disk 32 will cause the lst contacts of the combustion switch to close and thereupon the safety switch heater in operation. Instead, a running circuit is established traceable through l6 also closes the holding the following wires and elements: 9, HS, f, c, h, 26, lst, 28, i, R, and e. The combustion switch has in effect rendered the safety switch heater inoperative to warp the bimetal latch 20 upwardly. The resistance R is now the only resistance in. the running circuit.

Thus in either the cold stack or hot stack position of the combustion switch, there is a load on the upper half of the secondary i2, so as to minimize varying the available current for maintaining the relay coil energized. For minimum variation of the load on the transformer, the resistance SSH should be small in comparison with the resistance R.

Combustion failure after combustion has been established Intermittent ignition control The ignition mechanism Ion is de-energized upon combustion being established due to the' combustion switch reaching the position illustrated in Figure 5; In this position, the 2nd contacts of the combustion switch in Figure 9 (3rd in Figure 5) have energized, thereupon establishing atrip coil circuit through the following wires and elements: a, RT, 7', the trip coil TC, k, 38, 3rd (4th in Figure 4), 2nd (3rd in Figure 4), 26, h, c, HS and Q.

- Energization of the trip coil causes the armature 36 to be attracted as already explained in connection with Figures 1 to 8. Further-than as explained, the operation of the system shown in Figure 9 is similar to the operation of the system shown in Figures 1 to 8.

In addition to securing the advantages outlined, my system provides low voltage protection in the same manner as set'forth in my co-pending application hereinbefore referred to.

Some changes may be made in the construction and arrangement of the parts of my device without departing from the real spirit and purpose of my invention, and'it is my intention to cover by my claims any modified forms of structure or use of mechanical equivalents, which may be reasonably included Within their scope.

I claim as my invention:

1. In a control system for a burner having a fuel supply-motor and ignition means, a control circuit having a transformer providing a source of current supply and a relay therein for controlling the energization of said motor and the energization of said ignition means, a temperature responsive control switch in said control circuit for controlling said relay, said relay hav ing means operable upon energization to reduce the value of the current from said source of cur rent supply to said relay by using only a part of said transformer to maintain said relay energi'zed, said control circuit having also'therein a safety switch heater and a pair of resistances, a safety switch operable to render said control system inoperative upon energization of said safety switch heater for a predetermined period of time,- an electro-responsive circuit breaker for the circuit of said ignition means, a combustion switch having first contacts closed in the ab- When in such position, the safety sence of combustion and second and third contacts closed in the presence of combustion, said first contacts when closed shunting one of said resistances out of said circuit, said second contacts when closed shunting said safety switch heater out of said circuit and said third contacts when closed energizing said electro-responsive circuit breaker.

2. In a control system for a burner having a fuel supply motor and ignition means, a motor switch, an ignition circuit breaker, a temperature responsive control switch for said system, a safety switch heater, a pair of resistances, a relay, a holding switch, a combustion switch having first contacts closed in the absence of combustion and second and third contacts closed in the presence of combustion and electrical means including 'a transformer and a control circuit interconnecting the foregoing elements and operating upon closure of said control switch to (1) energize said relay to close said motor switch and thereby energize said motor and said ignition means and energize said safety switch heater and one of said resistances, all from said transformer (2) close said holding switch to effect a substantial weakening of the current supplied to said relay, said holding switch being connected to a point intermediate the ends of said transformer to effect such weakening (3) the combustion switch upon combustion occurring causes said second contacts to close and said first contacts to open, thereby substituting one of said resistances for saidsafety switch heater in said control circuit and (4) the third contacts of the combustion switch close to operate said ignition circuit breaker.

3. In combination with an electrically operated fuel burner including means for igniting the fuel burned thereby, a control system comprising a transformer, a relay having a winding, a switch controlling said fuel burner and said fuel igniting means, said switch being closed by said relay upon energization thereof to initiate operation of the burner, means operable to render said fuel igniting means inoperable while said burner is maintained in operation, a room thermostat controlling energization of said relay from the secondary of said transformer, a holdi'ng'switch operable by energization of said relay to thereafter supply current to said relay from a portion only of said secondary, a thermal time limit cutout switch controlling said system and including a resistance heater, a pair of resistances for circuit connection therewith, a combustion responsive means havi ng first contacts which are closed and second and third bontacts which are open in the absence of combustion, a first circuit including in series said transformer secondary, room thermostat, relay winding, cut-out switch heater and one of said resistances, said second contacts shunting said cut-out switch heater and said first cont-acts shunting the other of said resistances whereby upon combustion establishment said other of said resistances is substituted in the circuit for said cut-out switch heater, said other of said resistances having the approximate value of said cut-out switch heater, said one of said resistances remaining in circuit in series with said cut-out switch heater until combustion establishment and thereafter in series with the other of said resistances, said third contacts, upon being closedas a result of combustion establishment, causing operation of said means to render said fuel igniting means inoperable.

4. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a transformer, a circuit breaker for de-energizing said ignition means, a control circuit having a room thermostat therein, said control circuit including electro-responsive means operable by the secondary of said transformer for closing said motor switch, said electro-responsive means, upon energization, being effective to connect said electroresponsive means with a part of said secondary whereby said part only thereof maintains said electro-res ponsive means energized, a pair of resistances and a safety switch heater, 2. safety switch adapted for rendering said system inoperative upon a predetermined time period of energization of said safety switch heater and means for operatively de-energizing said safety switch heater upon successful combustion establishment comprising a combustion responsive mechanism having first switch contacts shunting one of said resistances and second switch contacts shunting said safety switch heater, said first contacts being closed in the absence of combustion and open in the presence of combustion and said second contacts being open in the absence of combustion and closed in the presence of combustion, said combustion responsive mechanism, upon successful establishment of combustion, operating said circuit breaker.

5. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a trans former, a circuit breaker for de-energlzing said ignition means, a control circuit comprising in series, the secondary of said transformer, a room thermostat and electro-responsive means for closing said motor switch, a pair of resistances and a safety switch heater in said control circuit, a safety switch adapted for rendering said system inoperative upon predetermined energization of said safety switch heater, means for operatively -cessful combustion establishment comprising a combustion responsive mechanism operable to connect said safety switch heater in said control circuit during the absence of combustion and to substitute one of said resistances for said safety switch heater in the control circuit upon establishment of combustion, said one of said resistances having the approximate value of said safety switch heater, a holding switch closed by energization of said electro-responsive means, said holding switch being connected with the center of said secondary and with said control circuit to maintain said electro-responsive means energized by one part of said secondary and the other elements in said control circuit energized by the other part thereof after closure of said holding switch, said combustion responsive mechanism, upon successful establishment of combustion, operating said circuit breaker.

6. In a control system for a burner having a fuel supply motor and ignition means, a control circuit having a transformer providing a source of current supply and a relay therein for controllin'g the energization of said motor, a temperature responsive control switch for controlling said relay, said relay having means operable upon energization to reduce the value of the current from said source of current supply to said relay by. us-

said relay energized, said control circuit having also therein a safety switch heater and a pair of resistances, a safety switch operable to render said control system inoperative upon energization of said safety switch heater for a predetermined period of time, a combustion switch having first contacts closed in the absence of combustion and second contacts closed in the presence of combustion, said first contacts when closed shunting one of said resistances out of said circuit and said second contacts when closed shunting said safety switch heater out of said circuit.

7. In a control system for a burner having a fuel supply motor and ignition means, a motor switch, a temperature responsive control switch for said system, a safety switch heater, a pair of resistances, a relay, a holding switch, a combustion switch having first contacts closed in the absence of combustion and second contacts closed in the presence of combustion and electrical means including a transformer and a control circuit interconnecting the foregoing elements and operating upon closure of said control switch to (l) energize said relay to close said motor switch and thereby energize said 'motor and said ignition means and energize said safety switch heater and one of said resistances, all from said transformer (2) close said holding switch to effect a substantial weakening of the current supply to said relay, said holding switch being connected to a point intermediate the ends of said transformer to effect such weakening (3) the combustion switch upon combustion occurring causes said second contacts to close and said first contacts to open, thereby substituting one of said resistances for said safety switch heater in said control circuit.

8. In combination with an electrically operated fuel burner, a control system comprising a transformer, a relay having a winding, a switch con trolling said fuel burner closed by said relay upon energization thereof to initiate operation of the burner, a room thermostat controlling energization of said relay from the secondary of said transformer, a holding switch operable by energization of said relay to thereafter supply current to said relay from a portion only of said secondary, a thermal time limit cut-out switch controlling said system and including a resistance heater, a pair of resistances for circuit connection therewith, a combustion responsive means having first contacts which are closed and second contacts which are open in the absence of combustion, a first circuit including in series said transformer secondary, room thermostat, relay winding, cut-out switch heater and one of said resistances, said second contacts shunting said cut-out switch heater and said first contacts shunting the other of said resistances whereby upon combustion establishment said other of said resistances is substituted in the circuit for said cut-out switch heater, said other of said resistances having the approximate value of said cut-out switch heater, said one of said resistances remaining in circuit in series with said cut-out switch heater until combustion establishment and thereafter in series with the other of said resistances.

9. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a transformer, a control circuit having a room thermostat therein, said control circuit including electroresponsive means operable by the secondary of said transformer for closing said motor switch, said electro-responsive means, upon energization, being effective to connect said electro-responsive means with a part of said secondary whereby said part only thereof maintains said electro-responsive means energized, a pair of resistances and a safety switch heater, a safety switch adapted for rendering said system inoperative upon a predetermined time period of energization of said safety switch heater and means for operatively de-energizing said safety switch heater upon successful combustion establishment comprising a combustion switch having first contacts shunting one of said resistances and second contacts shunting said safety switch heater, said first contacts being closed in the absence of combustion and open in the presence of combustion and said second contacts being open in the absence of combustion and closed in the presence of combustion.

10. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a transformer, a control circuit comprising in series the secondary thereof, a room thermostat and electro-resp'onsive means for closing said motor switch, a pair of resistances and a safety switch heater in said control circuit, a safety switch adapted for rendering said system inoperative upon predetermined energization of said safety switch heater, means for operatively de-ener-- gizing said safety switch heater upon successful combustion establishment comprising a combustion switch operable to connect said safety switch heater in said control circuit during the absence of combustion and to substitute one of said resistances for said safety switch heater in the control circuit upon establishment of combustion, said one of said resistances having the approximate value of said safety switch heater, a holding switch closed by energization of said electroresponsive means, said holding switch being connected with the center of said secondary and with said control circuit to maintain said electroresponsive means energized by one part of said secondary and the other elements in said control circuit energized by the other part thereof after closure of said holding switch.

11. In combination with an electrically operated fuel burner including means for igniting the fuel burned thereby, a control system comprising a transformer, a relay having a winding, a switch controlling said fuel burner and said fuel igniting means, said switch being closed by said relay upon energization thereof to initiate operation of the burner, means operable to render said fuel igniting means inoperable while said burner is maintained in operation, a room thermostat controlling energization of said relay from the secondary of said transformer, a holding switch 013- erable by energization of said relay to thereafter supply current to said relay from a portion only of said secondary, a thermal time limit cut-out switch controlling said system and including a resistance heater, a resistance for circuit connection therewith, a combustion responsive means having first and second contacts which are open in the absence of combustion, a first circuit including in series said room thermostat, relay winding, cut-out switch heater, resistance and said transformer secondary, said first contacts shunting said cut-out switch heater whereby upon combustion establishment said cut-out switch heater is rendered inoperable, said resistance remaining in circuit in series with said cut-out switch heater until combustion establishment and thereafter being alone in the circuit, said second contacts, upon being closed as a result of combustion establishment, causing operation of said means to render said fuel igniting means inoperable.

.12. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a transformer, a circuit breaker for de-energizing said ignition means, a control circuit having a room thermostat therein, said control circuit including electro-responsive means operable by the secondary of said transformer for closing said motor switch, said electro-responsive means, upon energization, being effective to shunt out part of said secondary whereby the remaining part only thereof maintains said electro-responsive means energized, a resistance and a safety switch heater, a safety switch adapted for rendering said system inoperative upon a predetermined time period of energization of said safety switch heater and means for operatively de-energizing said safety switch heater upon success ful combustion establishment comprising a combustion responsive mechanism having first switch contacts shunting said safety switch heater, said first contacts being open in the absence of combustion and closed in the presence of combustion, said combustion responsive mechanism, upon successful establishment of combustion, operating said circuit breaker.

13. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a transformer, a circuit breaker for de-energizing said ignition means, a control circuit energized.

by the secondary of said transformer having a room thermostat therein, said control circuit including electro-responsive means for closing said motor switch, a resistance and a safety switch heater in said control circuit, a safety switch' adapted for rendering said system inoperative upon predetermined energization of said safety switch heater, means for operatively de-energizing said safety switch heater upon successful combustion establishment comprising a combustion responsive mechanism operable to connect said safety switch heater in said control circuit during the absence of combustion and to render it inoperable upon establishment of combustion and a holding switch closed by energization of said electro-responsive means, said holding switch being connected with the center of said secondary and with said control circuit to maintain said electro-responsive means energized by one part of said secondary and the other elements in said control circuit energized by the other part thereof after closure of said holding switch having contacts closed in the presence of combustion and electrical means including a transformer and a control circuit inter-connecting the foregoing elements and operating upon closure of said control switch to (1) energize said relay to close said motor switch, thereby to energize said motor and said ignition means and energize said safety switch heater and said resistance all from said transformer (2) close said holding switch to effect a substantial weakening of the current supply to said relay, said holding switch being connected to a point intermediate the ends of said transformer to effect such weakening (3) the combustion switch upon combustion occurring causes said contacts to close, thereby shunting said safety switch heater from, and retaining said resistance in said control circuit.

15. In combination with an electrically operated fuel burner, a control system comprising a transformer, a relay having a winding, a switch controlling said fuel burner closed by said relay upon energization thereof to initiate operation of the burner, a room thermostat controlling energization of said relay from the secondary of said transformer, a holding switch operable by energization of said relay to thereafter supply current to said relay from a portion only of said secondary, a thermal time limit cut-out switch controlling said system and including a resistance heater, a resistance for circuit connection therewith, a combustion responsive means having contacts which are open in the absence of combustion, a first circuit including in series said room thermostat, relay winding, cut-out switch heater, said resistance and said transformer secondary, said contacts shunting said cut-out switch heater whereby upon combustion establishment said cut-out switch heater is rendered inoperable, said resistance remaining in circuit in series with said cut-out switch heater until combustion establishment and thereafter being alone in the circuit.

16. In a burner control system for a fuel supply motor and ignition means for the fuel supplied thereby, a motor circuit having a motor switch therein, the energization of said ignition means being controlled by said motor switch, a transformer, a control circuit energized by the secondary thereof having a room thermostat therein, said control circuit including. electroresponsive means for closing said motor switch, a resistance and a safety switch heater in said control circuit, a safety switch adapted for rendering said system inoperative upon predetermined energization of said safety switch heater, means for operatively de-energizing said safety switch heater upon successful combustion establishment comprising a combustion switch operable to connect said safety switch heater in series with said resistance in said control circuit during the absence of combustion and to connect only said resistance in the control circuit upon establishment of combustion and a holding switch closed by energization of said electroresponsive means, said holding switch being connected with the center of said secondary and with said control circuit to maintain said electro-responsive means energized by onepart of said secondary and the other elements in said control circuit energized by the other part thereof after closure of said holding switch.

BURTON E. SHAW.

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