US2445531A - Safety control system for burners - Google Patents

Description

JuIy-ZO, 19. 8- T. J-. MESH SAfETY CONTROL SYSTEM FOR BURNERS 5 Sheets-Sheet 1 Filed April 16, 1945 INVENTOR fi/z'ooa/rz JJYtJ/l BY 7141,

ATTORNEYS July 20,1948. T. J. MESH I 2,445,531

SAFETY CONTROL SYSTEM FOR BURNERS 27/500004- J'M'Ju w BY 9 W141,

ATTORNEYS July 20, 1948. 1'. J. MESH 2,445,531

smm cou'rRoL sYs'rEu won sunuaas Filed April 1a, 1945 v 5 Sheets-Sheet s INVENTOR 77/500005 I M's/r WW, o i/e44 ATTORNEY? T. J. MESH SAFETY CONTROL SYSTEM FOR BURNERS Filed April 16,1945

July 20, 1948.

.5 Sheets$heet 4 INVENTOR fi/iooomz JJYfJ/l BY 1 q. z a g ATTORQYS July 20, 1948, 'r. J. MESH SAFETY CONTROL SYSTEM FOR YBURNERS 5 Sheets-Sheet 5 Filed April 16, 1945 vide electronic Patented July 20,

SAFETY CONTROL SYSTEM FOR BUB'NEBS Theodore J Mesh, Easthampton, Mam, assignor to Gilbert & Barker Manufacturing Company,

West Springfield, Mass,, a corporation of Maosachusetts Application April 16,

16 Claims. 1

This invention relates to improvement in control systems for burners, such for example as those using liquid or gaseous fuel.

This application is a continuation in part of m application Serial No. 542,841, filed June 30, 1944, andwhich has become abandoned.

The invention has for its general objects to provide an improved burner control system which is relatively simple, can be produced at relatively low cost, requires little servicing, is reliable in operation and is exceedingly compact.

The invention makes use of a well known form of control motor for actuating the switch or switches of the system. A small, alternating current, synchronous motor, set into action on a call for heat by a thermostat switch, drives, through gear reduction mechanism, including an electromagnetically-operated clutch, a timing shaft having thereon means for actuating the switch or switches of the system at a predetermined time or times after the control motor is started. The timing shaft is turned in one direction only by the control motor and, when so turned, winds up a spring which is later used to return the shaft to its initial position, when the clutch is released by deenergization of its electromagnetic-operating means on opening of the control motor circuit, to interrupt the transmission between the shaft and the control motor.

The invention has for one object to provide means operable with a very small amount of power for stopping the control motor substantially instantaneously, when combustion occurs at the burner following the starting of the burner by a switch actuated by the timing shaft, and for magnetically holding the motor and its timing shaft in its stopped position with the clutch engageda failure of combustion allowing the shaft to move beyond said position and stop the burner.

The invention has for another object to promeans, set into action by any suitable means responsive to the occurrence of combustion in the burner, for effecting the stopping of the control motor and the magnetic holding of it in the aforesaid position without the use of switches or relays and without opening the circuit of the control motor.

The invention has for a further object to provide, as a control element for said electronic means, a phototube located to respond to the presence of flame at the burner and adapted to set said means into action.

The invention has for another object to provide a grid-controlled vacuum or gaseous-discharge rectifier tube having its plate-cathode circuit con- 194 5, Serial No. 588,451 (Cl. 158-28) nected directly across the terminals of the field winding .of the control motor and set into action by a suitable combustion responsive control, whereby to rectify the alternating current and produce a' pulsating direct current in a short circuit across said winding for the purpose of stopping the motor and magnetically holding it in its stopped position.

The invention has for another object the provision in a control system of the class means for preventing resetting of the timing shaft by its spring, whenever the burner is stopped by the safety means because of failure of combustion, for the purpose of preventing recycling of the control unless and until the preventing means is manually released.

The invention has sion in a control system of the class described, of means for compelling resetting of the timin shaft to its initial position as a condition precedent to a subsequent cycle of operation of the shaft, for the purpose of providing a safe failure of the control in case the timing shaft fails to reset because of a broken reset spring, or sticking of the timing shaft or motor in on any other reason.

The invention will be disclosed for illustrative purposes in connection with the accompanying drawings, in which,

Fig. 1 is a diagrammatical view of a burner.

control system embodying the invention:

Figs. 2 and 3 are diagrammatical views showing modifications of the control system;

Fig. 4 is a sectional view of the control motor, its timing shaft, gear reduction mechanism, and clutch;

Fig. 5 is a diagrammatical view of the control motor, timing shaft and the switches actuated thereby; and

Figs. 6 and 7 are diagrammatical views showing other modifications of the control system.

Referring to Fig. 1, l and 2 are the hot and ground terminals of a 115 volt, cycle, alternating current supply. The terminal I is connected by wires 3, l and 5 to one terminal of the primary 6 of a step down transformer I. The other terminal of the primary 6 is connected by a wire I to the terminal 2. Interposed between wires I and l is a normally-closed limit control switch 9, such for example as a switch opening in response to excess pressure of steam in the boiler, being heated by the burner. Interposed between the wires 4 and I5 is a safety lockout switch III, which is normally closed but can be opened'automatlcally on failure of combustion, as will later appear. Un-

descrlbed of.

for another object the proviposition or for der normal conditions, the primary circuit of transformer 1 is closed.

This transformer has two secondary windingsone, marked supplying current at 24 volts for example, and the other marked l2, supplying current at 6 volts for example. The 24 volt winding is in a circuit |2 including in series a room thermostat switch l4 and the coil ll of a relay, having two sets of mating contacts l2 and I1, respectively, the contacts or each set engaging when coil ll is energized.

One of the contacts I6 is connected by a wire I! to switch l and through the latter, wire 4, limit switch 9 and wire 2 to one terminal I of the alternating current supply. The other of contact I6 is connected by wires i9 and 20 to a capacitor 2| and through the latter and resistors 22 and 22 to one terminal of the main field winding 24 of a control motor such for example as a self-starting synchronous electric motor. The other terminal of this field winding is connected by wires 2|, 28 and 21 to the ground terminal 2 of the alternating current supply. Thus, on closure or the thermostat switch H, the relay will be energized and contacts I6 closed to start the control or timing motor.

This motor actuates three switches in sequence. They are, in the order of their actuation-a switch 22, which is initially open and is closed by operation of the timing motor a predetermined time after the motor is started; a switch 29 which is initially open and is closed by operation of the timing motor a predetermined time after switch 22 is closed; and the described switch III. which is initially closed and is opened it and when the timing motor continues in operation a predetermined time after the closing of switch 28.

The switch 29 controls the burner motor 20 and the ignition means 3|, setting them into opterminal 2.

The switch 28 connects a rectifying means across the field winding 24 of the timing motor. The purpose of this means is to stop the timing motor, if combustion occurs before the motor moves far enough to open switch Ill. The rectii'ying means as herein shown, is electronic. Preterably, such means consists of a grid-controlled, gaseous-discharge rectifier tube 25, such as a thyratron, having a plate 36, grid 31, cathode 22, shielding grid 39 and a. tube heater 40. The plate-cathode circuit of this tube is suitably coupled to the. field 24 of the timing motor. As shown, the plate 36 is connected by a wire 4| terminal of switch 28 is connected by a wire 43 to the cathode 28. The shielding grid 39 is also connected to wire 42.

The tube heater 4!! is connected by wires 44, 45 and 4B in a series circuit with the secondary |2 of the transformer and with the contacts i1. Thus, on a call for heat when thermostat switch l4 closes, the contacts H are engaged and the heater is supplied with low voltage current. The heating of the tube and the operation of the 28 as by a wire and 45.

The electronic tube 25 is set into action by means of a. suitable combustion control when combustion occurs. A desirable form of combus- Bias for the grid of tube II is voltage drop across the resistor 22, which drop may, for example, be 6.75 volts. This bias is applied to the grid through a capacitor ll of from provided by the between the resistors 22 and 22. nects the other terminal of the wire BI and thus to grid 21.

When the electronic tube 25 is set in action by the phototube 41 in response to the presence of flame or by any other suitable combustion-responsive means, a pulsating direct current fiows through wires 4|, 25 and 42 01' such magnitude as to produce for all practical purposes the eilect of a short circuit across the motor field 24 on the positive half cycles of voltage. Impedance is included in the circuit with the motor field, first for the purpose of limiting the current fiow in the rectifier during the aforesaid short circuit periods and, second, for the purpose of dropping the motor voltage across the motor field 24 to a A wire 22 concapacitor II to the wires 4|, 2! and 42.

It will be noted that the impedance which is in series circuit with the timing motor is composed of the capacitor 2|, which may for example have a capacity oi 1 microiarad, and the resistors 22 and 22, which may for example respectively be 01' 500 and ohms resistance. The circuit or the timing motor is in partial resonance with the result that the arithmetical sum of the voltages across the motor, capacior and resistors is more than the applied line voltage 01' 115. The vector sum of these voltages is nevertheless 115. This provides a convenient method of obtaining full motor voltage, without the use of a transformer, and at the same time securing a good series impedance to limit the current in tube 22, when it is actuated. These resistors are chosen to give exactly the rated voltage at the timing The timing motor is shown in section in Fig. 4. Its rotor 44 is fixed. to one end of a shaft 44, which is rotatably mounted in hearings in the casing I4 and which has fixed to its other end a pinion 51. This shaft is axially movable. A spring '4 moves it to the right into, and yieldingly holds it in, the illustrated position, in which the pinion 51 is out of meshwith a gear I of a gear reduction mechanism. The latter comprises the pinion 51, the gear 59 and a train of gears 40, which are mounted in casing 54 and drive a timing shaft 6i. When the field 24 of the timing motor is energized, the rotor 44 is drawn by magnetic attraction to .the left until the magnetic ring 62 of the rotor comes into line with the pole piece member 43. As a result. the pinion II will be moved into mesh with gear 49 and, as the rotor rotates, the shaft 4| is turned at a definite time rate, say for example, one revolution-per minute.- The pinion I1 and gear 49 constitute a clutch operable by electromagnetic means comprising the field 24 and armature 54 of the timing motor. The details of the motor construction are not important to the present invention anddescr-iption of them is deemed unnecessary. The motor construction may, for example, be substantially the same as is shown in the Haydon Patent No. 1,996,375, dated April complete disclosure of the motor if such is necessary or desired. As more fully disclosed in said patent, ashaded pole winding, comprising short circuited copper rings 42' surrounding the polar projections'ii', is used for starting purposes.

The timing shaft 6i, and the switch-actuating means thereon, are shown in diagrammatical form in Fig.- 5. This shaft, as shown, carries three cams III, II and 12 for actuating the switches 29, 29 and I0, respectively. The shaft 4i can be turned in a clockwise direction by the timing motor until a stop If, movable with the shaft, engages the right hand side of a fixed abutment I4. A spring 15, connected at one end to the shaft and at the other end to a stationary member 14, is adapted to be wound up by the clockwise rotation of the shaft. Them-when the motor field 24 is deenergized, the magnetic pull on rotor 54 is broken and spring 58 moves it into the position illustrated in Fig. 4, disengaging pinion II from gear 59, whereupon the spring II 1935, to which reference is made for a more will turn shaft BI in a counterclockwise direction back into the illustrated position, wherein the stop I3 abuts the left hand side of abutment I4.

In the particular example shown in Fig. 5, the shaft II turns clockwise at the rate of one revolution a'minute or 6 degrees in one second. In the zero and rest position shown, the cam followers of all three switches are entailed with the low dwell portions of their respective cams, whereby the switches 29 and 29 are open and switch II is closed. Cam I9 starts its rise in 7 seconds and completes it in 12 seconds, whereupon switch 28 will be closed. The plate-cathode circuit to the field of the timing motor 24 is thus established. This switch 28 will be maintained closed by the engagement of its follower with the high dwell portion of cam III, untilthe shaft reaches the end of its clockwise'travel or until stop it abuts the right hand side of abutment 14, when the follower rides off onto the low dwell portion of the cam and the switch 24 opens. Cam II starts its rise in 12 seconds from zero position and completes it in 1'? seconds, whereupon switch 29 is closed to start the burner motor I. and the ignition means ll. This switch 29 is maintained closed by the high dwell portion of cam 'II until the shaft 8i completes its clockwise travel, when the switch is opened because its cam follower rides off the high dwell portion of cam II. Cam I2 starts its rise in 42 seconds from zero position and completes it in 47 seconds, whereupon switch It will be opened. Once opened, switch III cannot be closed until it has been manually reset. This can be accomplished in various ways, as will be readily understood by those skilled in the art. As shown conventionally herein, the blade ll of switch III is 0! resilient material and, when its free end is snapped past the pointed end of abutment II, it is retained by the latter in open position, as indicated by dotted lines. The blade Il may be moved back into its normal position by manual pressure on the reset button I9, provided that the cam I2 is then so positioned that some part of the low dwell portion of the cam lies opposite the cam follower, which occurs at both ends of the range of travel of shaft 8 I.

The operation will next be described. On a demand for heat from the burner, the thermostat switch I4 closes, thereby energizing the relay II. The latter, when energized, closes the two sets of contacts l6 and I1. A circuit is established from transformer secondary I2 through the heater 40 of electronic tube 35. Another circuit is established through the timing motor 24, as follows: from terminal I, wire 3, limit switch 9, wire 4, safety switch I0, wire II, contacts I6, wires I9 and 20, capacitor 2|, resistors .22 and 23, field 24, wires 25, 26 and 21 to terminal 2. The circuit to the timing motor and the circuit to the heater are simultaneously established. The heating of tube 35 requires approximately ten seconds and twelve seconds elapses before the shaft BI has traveled far enough to close switch 28. The closing of the latter serves to connect the plate-cathode circuit of tube 38 directly across the motor field 24. After the shaft 6| has been turning for 1'1 seconds, the switch 29 closes and this starts the burner motor 34 and the ignition means ii, the circuit being traced as follows: from terminal I, through wire 3, limit switch 9, wire -4, safety switch II, wire I8, contacts I8, wires I9 and 32, switch 29, wire 31 to motor 3|! and i nition means II, and then by wires 34 and 21 to terminal 2. The timing motor continues to turn shaft 4| in a clockwise direction until combustionoccurs, or until safety switch ill opens, whichever event occurs first. In the particular example herein disclosed, an interval of 30 seconds after closing of the switch 28 is required for the shaft ii to turn to the position wherein the safety switch II opens. Normally, combustion will occur within this interval. If combustion does occur within this interval, the phototube 41 starts the electronic tube 35 and the timing motor 24 is stopped and held magnetically in its stopped position. If combustion does not occur within said interval, the timing shaft 4| continues to be turned by the timing motor and will eventually cause safety switch iii to open and be held open until manually reset. Opening of switch I! will deenergize the primary 6 of transformer I, thus deenergizing relay I5, causing the opening of contacts i6 and II, whereupon the burner motor 20 and ignition means ii are stopped and the timing motor and the heater of tube 35 are deenergized. 0n deenergization of the timing motor, shaft 4| will be turned backwards by spring 15 to the initial p sltion illustrated in F18. 5. Switches 28 and 28 will thus be opened and cam ll will become so positioned that switch I8 can be manually closed by the reset button 19. On closure of switch it, recycling will occur, the relay l closing con- 1 tacts l8 and I1, starting the timing motor and the heater for tube 35, whereby the switches 28 and 29 will be successively closed as before. If combustion then occurs, the timing motor will be stopped as described. Assuming that combustion does occur and continues until the demand for heat is satisfied, the thermostat switch it will open, deenergizing coil l5, causing contacts i5 and H to open, whereby the heater 48, motor 38, ignition means 3i and the field 25 of the timing motor are deenergized. As the timing motor is deenergized, the clutch, comprising the gears 51 and 59, is opened, allowing shaft 6| to be turned back to zero position by spring 15. This movement of shaft 6i will open switches v28 and 28 in readiness for another cycle of operation when another demand for heat occurs. If during operation of the burner, the limit control switch 8 should open, the apparatus is stopped in the same manner as if the safety switch I0 opened, except that it will recycle without manual resetting when the limit is satisfied. If flame failure occurs during any run after combustion has been initiated, the timing motor will start up and cause .the switch ill to open unless combustion occurs during the 30 second interval described, in which case the timing motor will stop and normal burner operation will continue.

The sensitivity of the combustion control to response to flame is controlled by the size of the capacitor 5| and the amount of the grid bias obtained by the drop in voltage through the resistor 23. By these means, the intensity of flame necessary to secure actuation of the electronic tube and resultant stopping of the timing motor may be varied within limits as desired. If for example, the burner nozzle becomes partially plugged, resulting in a poor and stringy fire, the timing motor will be released and the cam shaft 8i will be driven on until the safety switch i8 opens.

The control is designed to fail safe in the event of failure of any of its component parts. In the event of a broken or defective phototube 41 or open wiring in the phototube circuit, the tube will not operate. Accordingly, the timing motor will continue in operation until it opens switch 10 and causes a safety shut down of the burner. In the event of a short-circuited phototube, shorted or grounded phototube wiring, moisture or leakage across the phototube sufficient to cause trouble, stray light of sufficeint intensity to cause trouble, after-fire in the combustion chamber, or a defective electronic tube which operates in the absence of flame, the tube 35 is activated as soon as switch 28 is closed and the timing motor is locked before it has turned shaft 8| far enough to close the switch 29, whereby the burner cannot start. J

In case there is a short circuit from the plate to the cathode in tube 35, the field 24 of the timing motor will be deenergized and the gear 51 will move out of mesh with gear 58, allowing spring 15 to reset shaft iii to zero and open switch 28. The timing motor will again start and the described cycle of operation will be repeated indefinitely. However, no harm results because the current flow is limited by capacitor 2| and resistors 22 and cannot start.

' In case thecapacitor 2| becomes short circuited, the tube 35 will be unable to lock the timing motor and will be overloaded in attempting to do so. The timing motor will turn until the safety switch it opens and stops the burner. The resistor 22 may burn out as the result of heavy current through tube 35 and, if it does, the field of the timing motor is deenerglzed and the timing shaft automatically resets to zero position. If this same capacitor has an open circuit in the connection to its plates, the timing motor cannot start and the burner cannot be started. If the capacitor 5i becomes short circuited, the tube 35 is activated to lock the timing motor as soon as switch 28 closes and the burner cannot start. If the capacitor II is open circuited, either of two things may happen, via, the tube 35 will be activated when switch 28 closes in which case the burner cannot start, or the tube 35 will not be activated at all and there will be a safety shut-down of the burner when switch i0 opens.

As to resistor failures, if resistor v23 is short circuited, the tube 35, as the result of loss of grid-bias, will lock the timing motor as soon as switch 28 closes and the burner cannot be started. If this resistor is open circuited, the timing motor cannot start. If resistor 22 is short circuited, the current in the timing motor and in the tube 35 will be slightly higher than normal but otherwise has no harmful effect.

In the event that the relay I5 is burned out, the timing motor cannot start and operation of the burner cannot occur. If the timing motor is burned out, or grounded or short circuited, the burner cannot start.

As to switch failures, if switch 28 fails to close, the tube 35 cannot lock the timing motor and the switch I0 is eventually opened to cause a safety shut-down of the burner. If switch 28 fails to open, because its contacts are welded together 28 and because the burner or for other reasons, all functions will nevertheless occur normally. This switch merely prevents the application of plate voltage to the tube 35 until the tube has heated up. If switch 28 fails to close, the burner cannot; start and the timing motor continues to operate-until switch III isopened to cause a safety shut-down of the control. In case switch 29 fails to open for any reason, the burner will start immediately on the closing of thermostat switch i4, If combustion occurs, the timing motor will be locked but if it does not occur, the timing motor will continue to operate until switch l0 opens and causes a safety shut-down of the burner. If switch i0 fails to close, the burner cannot be started and the entire control system is dead. It switch I8 fails to open for any reason, a safety shut-down will nev-- ertheless occur because the shaft 8i will continue to turn until the stop 13 engages the right hand side of abutment 14, when switches 28 and 28 will open because their cam followers will ride off the steep drop, which interconnects the high and low dwell portions of the cams. The cam followers are locked in this position and manual attention is necessary before the burner can again be started. By manually opening the thermostat switch or by opening the circuit in which this switch is located, the electromagnetic pull on the clutch is broken and spring 15 can then turn the camshaft 6i back to its initial position, after the several cam followers have been pulled radially outward far enough to release the cams for amass! movement. It is not necessarily essential in all cases to have the cam followers thus locked as described.

In case of failure of shaft 8| to reset because of a broken reset spring I! or because the clutch gears do not disengage or because of excessive friction on the shaft M, the timing motor will drive the shaft to running position, where switch 28 closes in the usual way. The same protection against combustion failure is present. The burner continues to operate until the thermostat is satisfied, when the relay contacts open and stop the burner and th timing motor. The shaft 8I, however, does not reset; On the next call for heat, the burner starts immediately on closing of thermostat switch I4 and the timing motor starts. The tube 80 cannot lock the timing motor until its cathode is heated up and this takes from 7 to 10 seconds. Hence. camshaft 8| is driven along from its abnormal advanced starting position toward the safety shut-down position. About one third of the time interval between running and safety shut-down positions is used up. On the next succeeding call for heat, the burner will again operate as described, and shaft 8i will be moved close to safety shut-down position using up another third of said interval. On the next succeeding call for heat, the burner will again operate as described and this time, before the tube 80 can 'cause the timing motor to lock, the camshaft 8| will have moved far theless this operation would be likely to occur only at rare intervals following the failure of some other part.

In Fig 3, another variation of the control system is shown. Here the switch 28 is dispensed with as in Fig. 2 and, in addition, the safety switch I is omitted. The wires 4 and are directly interconnected instead of being connected enough to cause switch I0 to open and cause a safety shut-down of the burner.

The invention has been described in its complete form. However, it is possible to dispense with some of the elements described and still obtain many of the advantages of the invention.

For example the switch 28 with its actuating cam 10 may be omitted if desired. Such an arrangement is shown in Fig. 2, wherein a single wire 48' connects oneterminal or the timing motor 24 to the cathode 88 and shielding grid 88 of tube 88, instead of the wires 42 and 48 shown in Fig. l.- All other connections are the same as in Fig. l and the operation is substantially the same, differing only in that plate voltage is immediately applied to the tube 85, when thermostat switch I4 closes, instead of waiting until the cathode 88 has become heated. The switch 28 is a refinement which, while often desirable, is nevertheless not essential for the reason that no harm is done to the tube 85 provided that sumcient grid bias is present to prevent flow of plate current until such time as the tube cathode has ,reached its normal operating temperature.

The operation of the control system of Fig. 2 is essentially the same as the system of Fig. 1. There is the same protection against failure of component parts of the system, as above described in connection with Fig. 1, except for that failure due to a short circuit between the plate and cathode of the electronic tube 88. With switch 28 omitted, such a failure results in a permanent short circuit of the timing motor 24, which therefore can never start, instead of continuous recycling of the timing motor as previously described. A further advantage is that a shorted circuited phototube, or similar failure, will cause a premature locking of the timing motor as soon as the tube heater reaches operating temperature (in 7 to 10 seconds), rather than at the time of closing of switch 28 (12 seconds) as described in connection with Fig. 1. While this may be an improper method of operation of certain electronic tubes, such as thyratrons, neverthrough the switch I0 as heretofore. With switch I0 omitted, a safety shut-down is effected, as above described, when the shaft 8| travels to theend of its range of clockwise movement. The switch 28 will thenopen and stop the burner. Recycling will occur, when thermostat switch I4 is opened or its circuit otherwise opened, and the follower of switch 28 is drawn radially outward far enough to release the cam for return movement to zero position by spring I5.

In Fig. 6,there is shown an improved control system which provides protection in case the control shaft 8| fails to reset for any reason. In this system, the shaft BI is driven in one direction (clockwise) by the rotor 54 of the timing motor from the initial position shown until the timing motor is stopped by the occurrence of combustion or, in case combustion doesnot occur, to the limit position, wherein the stop I8 abuts the opposite side of the fixed stop I4. The spring I5, as before, tends to reset shaft 8i, whenever the field winding 24 of the timing motor is deenergized and the clutch opens. The shaft Si in this case carries a single cam having a rise of 45 degrees, an ensuing highdwell ofv degrees and then a low dwell of degrees. .A spring switch blade 8I carries a roll 82 which is adapted to ride on cam 80 and which is pressed against the cam by the spring of the blade or in any other suitable way. The blade carries a contact 88 which is adapted to engage a contact 84, when roll 82 rides on the low dwell of the cam, and which is adapted to be disengaged from contact 84 and engaged with a second contact 80, when the roll 82 rides on the high dwell of the cam.

The contacts 88 and 84 are in series in the primary circuit of transformer I. This circuit may be traced as follows, from terminal I by wire 88, limit switch 8, wires 81 and 88, contacts 84 and 88, blade 8|, wire 89 to primary 6 and thence by wire 80 to terminal 2. The primary 6 is thus energized. The relay coil I5, as before, is controlled by a room thermostat switch I4 in a low tension circuit including the secondary II. wires 8|, 82, 88 and 84, and a pair of contacts 88 and 88, which are normally held in engagement by a sprin 81. The relay coil I5, when energized by closing of thermostat switch I4 on a demand for heat, closes two pairs of contacts. The contacts 88 and 88 of one pair are connected by wires I00 and IOI to wires 88 and 88, respectively, and thus they are in parallel with the contacts 88 and 84. The contacts I02 and I08 of the other pair control the timing motor. Contact I08 is connected to wire IOI. Contact I02 is connected by a wire I04 to a capacitor I05 and the latter is connected by a wire I06 to a resistor I01. The latter is connected by a wire I08 to one terminal of the main field winding 24 of the timing motor.

The other terminal of winding 24 is connected by circuit to the primary I is maintained because the turn Y4 revolution per minute, for example. Thus,

the burner motor 80 and ignition 8| are rendered active in 10 seconds, which gives sufficient time for the heater 40 to heat the electronic tube 88 in case such action is required. As shown, the heater 40 is permanently connected b wires 8 and I to the secondary I2 and is not cut out by a switch, as heretofore described. Thus, the electronic tube 88 will normally be heated. However, if the burner is stopped by the limit control 8, the circuit of primary 8 will be opened and the secondary I2 which supplies the heater 0, will not be energized and thus the tube 88 will .be cool, when the burner is next started. But

the burner cannot be started by the subsequent closing of the limit control because the relay will drop out when the transformer 1 is deenergized and thus separate the contacts 88 and 88, causing a break in the circuit to primary 8 which break cannot be closed except by the closure of contacts 83 and 88, which occurs only after shaft 8| has been reset by its spring, following deenergization of the motor field 24 by the opening of contacts I02 and I08, when the relay dropped out.

The electronic tube 88 functions as before to stop the timing motor in the event that combustion occurs. Its plate 88 is connected by a wire 8 to wire I08 and its cathode 88 is connected to wire I08. Thus, the plate-cathode circuit is connected in parallel with the winding 24 of the timing motor. One terminal of the phototube I1 is connected by a wir ||8 to wire H5 and thus to the plate 88 while the other terminal is connected by wires II! and H8, resistor H8 and wire I20 to the grid 81. Bias for the grid is provided by the voltage drop across the resistor H0. This bias is applied to the grid through a capacitor 8|, the latter being connected by wires I and I22 to the wires H8 and II I, respectively. The resistor I I8 is added to secure final or subsequent adjustment of control sensitivity. The shielding grid 88 is connected to wire I08. One wire III of the heater supply circuit is also connected to wir I08 by a wire I 28. The circuits to the electronic tube differ slightly from those heretofore described. The phototube 41 is connected directly to the plate 86 instead of being grounded. The cathode 38 runs at practically ground level (except for the drop of a few volts in resistor III) and more stable operation is secured in this way. Also, some metal tubes, which may be used, have their metal shell tied to the cathode and it would be objectionable to have this shell alive to the ground. A capacitor I24 of .1 microfarad capacity is respectively connected by wires I 28 and I28 to the wires I06 and III for the purpose of eliminating radio interference. As one specific example, the capacitor I08 is of 1 microfarad capacity, resistors I01 and 0 are each of 150 ohms and one watt rating, resistor H8 is of A megohm and one-half watt rating, and the timing motor is rated at 110 volts and normally draws 3.6 watts from the line.

While the arrangement of Fig. 6 differs in detail from that before described, it functions in the same general manner, That is, the P O Q- tube on receiving light from the burner flame activates the tube 88 and causes the flow of unidirectional current through the winding 28 of the timing motor to lock the rotor 88 of the same and thus timing shaft 8|.

It will be clear that. if combustion occurs during the 30 second interval when roll 82 is riding on the 135 degree high dwell of cam 80, the shaft 8| will be stopped and held in stopped position by the locking of the timing motor. When the demand for heat is satisfied. thermostat switch I4 opens, deenergizing relay II, which drops out, thereby opening the circuit to the winding 28 of the timing motor and the circuit of the primary winding 8. The clutch of the timing motor then opens and spring 18 moves the control shaft 8| back to its initial position. This results in stopping the burner by the separation of contacts 88 and 88 and in the reestablishment of the circuit to the primary 8 by the engagement of contacts 88 and 84.

Should combustion not occur, the phototube 81 will not activate the tube 88 and the timing motor will not be locked. Hence, shaft 8| will continue its clockwise travel until the pin 18 engages stop I8. A spring latch |2l,.which is moved out by pin I8 as it passes, moves back into position to prevent return movement of the pin and thus resetting of shaft 8|. During the clockwise travel of shaft 8|, the roll 82 ran off the end of the high dwell onto the low dwell of cam 80, and thus caused the contacts 88 and 88 to separate and stop the burner and also caused the engagement of contacts 88 and 88 to close the initial circuit to primary 8. The timing motor is still energized because the demand for heat is not satisfled, but it cannot turn shaft 8| clockwise because of stop II. The spring 18 is prevented by the motor torque from turning the shaft counterclockwise. If the motor is deenergized by manually opening the thermostat switch, the spring I8 cannot completely reset shaft 8| because of the latch I21.

To recycle the control, the latch I2! is man ually released by pushing button I28 which turns bellcrank I28 and by means of a link I pulls the latch out. This movement of the bellcrank also separates the above described contacts 88 and 88. Separation of these contacts opens the relay circuit, causing the contacts 88 and 88 and I02 and I08 to separate. The primary circuit of the transformer I is thus opened and the timing motor is stopped. The spring I8 can now move shaft 8| back to initial position. As shaft 8| moves back, the contacts 88 and 88 will again be separated and the contacts 88 and 88 will again be engaged but the burner will not start because con-. tacts 88 and 88 are separated. As shaft 8| moves into its initial position, contacts 88 and 88 separate and contacts 88 and 88 engage. The circuit to the primary 8 is reestablished and the control is conditioned to respond to another call for heat.

It will be noted that the control shaft must be reset before it can again be moved in the direction necessary to start the burner. Hence, if the reset spring breaks, or the shaft 8| sticks in its bearings or the timing motor sticks in "on".

transformer 1 is held open by the then separated contacts 83 and II.

The system of Fig. '7 is generally the same as that of Fig. 6 with the following exceptions. The cam 83' has a high dwell of 315 degreeswhich maintains contacts 83 and 84 separated and the contacts 33 and 85 engaged at all positions except the initial angular position of 45 degrees. The burner is stopped on safety by the momentary opening of the thermostat circuit by separation of the contacts 95 and 98. This occurs in 30 seconds after the burner switch is closed, if combustion does not occur. Separation of these contacts is effected by causing the pin 73 to engage the spring blade l3l, on which contact 35 is mounted, and move it away from contact 98. This results in the dropping out of the relay and the stopping of the burner and the timing motor. Then, the shaft Bi starts to turn back by spring 15 and pin 13 .moves back until it is stopped by latch I21. The contacts 95 and 98 thus reengage. The latch is released, as before, by pressing on the button I23 which draws out the latch in the same way as described in connection with Fig. 6. As in Fig. 6, resetting of the shaft Si is necessary to a subsequent operation of the burner. The contacts 83 and 85 must separate and the contacts 83 and 84 must engage as a condition precedent to a subsequent operation of the burner. If the contacts Bil-and 35 should weld together the burner could not be started because the contacts 83 and 34 must engage before the transformer can be energized. The system of Fig. 7 has the advantage over the system of Fig. 6 that the timing motor is deenergized whenever the burner is stopped by the safety means. 7

In the system of Fig. 6 and also that of Fig. 7, the circuit of the timing motor is in resonance before the tube 35 is activated. The circuit in each case is resonant and is 50 arranged by the use of the capacitor I05 and the resistors I01 and H that the voltage across the terminals of the main field winding of the timing motor is higher than the line voltage before the tube fires. For example, the voltage across the motor may be 125 with a line voltage of H5. With this arrangement, a large drop in line voltage can occur without reducing the voltage applied to the motor to such an extent that the motor cannot operate the timing shaft. For example, even if the line voltage drops to 85 volts, the voltage across the motor will still be about 93 volts which is sufficient for the purpose. When the tube 35 is activated, the resonance of the timing motor circuit is destroyed and the voltage across the terminals of said field winding drops below line voltage,

.say to 105 volts. Low voltage protection is secured by adjusting the relay l to pick up at about 95 volts and drop out when the voltage drops below 85. There will be no chattering of the relay, due to low voltage operation, because the instant the relay contacts open, the relay drops out and it can not pick up again until the voltage rises to 95 and at this voltage there will be no chatter.

The component parts of the system are for the most part standard articles which can be bought in quantities at low unit cost. Such are the electronic tube, phototube, resistors, capacitors, relay, switches, and transformer. The timing motor, including the timing shaft, gear train, with magnetic gear shift or clutch and reset spring, is also a standardarticle and one needs to add only the special cam or cams needed to actuate the switch or switches desired. There is nothing of a special or complicated nature to be manufactured and the various parts may be obtained and assembled into the system described at relatively low cost.

The various parts of the, system may be assembled into a very compact unit occupying very little space. The complete timing motor unit occupies very little space and may be held in the palrn of one hand. The switches may be the so-called micro" switches, which are very small. The relay and transformer need be no larger than the timing motor unit. It is readily possible to mount all the parts in a space no larger than that occupied by the ordinary stack thermostat switch.

The invention thus provides an improved burner control which is simple, compact, relatively inexpensive to manufacture and one which is reliable in operation and unlikely to require much servicing. The control provides all the necessary safeguards against failures of the burner and against failure of the component parts of the system.

I claim:

1. In a burner control system, an alternating current timing motor, an electric circuit including said motor and an impedance, means to close said circuit on demand for heat from the burner and to open it when said demand is satisfied, an electronic tube having its plate-cathode circuit coupled to the terminals of said motor, a switch actuated by said motor a predetermined time after it is started to start the burner, a second switch actuated by said motor at another and later predetermined time after starting of the motor to stop the burner, means responsive to combustion at the burner to activate said tube and cause'said motor to be stopped and magnetically held in its stopped position, whereby on failure of combustion at the burner the motor continues to turn and actuate said second switch to stop the burner.

2. In a burner control system, an alternating current timing motor, an electric circuit including said motor and an impedance, means to close said circuit on demand for heat from the burner and to open it when said demand is satisfied, an electronic tube having its plate-cathode circuit coupled to the terminals of said motor, a switch actuated by said motor a predetermined time after it is started to start the burner, a second switch actuated by said motor at another and later predetermined time after starting of the motor to stop the burner and the timing motor, means responsive to combustion at the burner to activate said tube and cause said motor to be stopped and magnetically held in its stopped position, whereby on failure of combustion at the burner the motor continues to turn and actuate said second switch to stop the burner and the timing motor.

3. In a burner control system, a single phase alternating current timing motor, an electric circuit including said motor and an impedance, means to close said circuit on demand for heat from the'burner and to open it when said demand is satisfied, an electronic tube having its plate-cathode circuit coupled to the terminals of said motor, a switch actuated by said motor at a predetermined time after it is started to start the burner, means responsive to combustion at the burner to activate said tube and cause said motor to be stopped and magnetically held in its stopped position. and means to stop the burner operable by continued movement of said motor after closing of said switch on failure of said tube to stop the motor.

4. In a burner control system, an altematins current timing motor, an electric circuit including said motor and an impedance, means to close said circuit on demand for heat from the burner and to open it when said. demand is satisfied, an electronic tube having its plate-cathode circuit coupled to the terminals of said motor, a switch actuated by said motor a predetermined time after it is started to start the burner, a phototube responsive to combustion at the burner to activate said tube and cause said motor .to be stopped and held in its stopped position,'and means to stop the burner operable by continued movement of said motor after closing said switch on failure of said tube to stop the motor.

5. In a burner control system, an alternating current timing motor, an electric circuit including said motor and an impedance, means to close said circuit on demand for heat from the burner and to open it when said demand is satisfied, an electronic tube having its plate-cathode circuit coupled to the terminals or said motor, a switch actuated by said motor a predetermined time after it is started to start the burner, a phototube responsive to combustion at the burner to activate said tube and cause said motor to be stopped and held in its stopped position, and means to stop the burner operable by continued movement of said motor after closing of said switch on failure .of said phototube to cause said motor to stop.

6. In a burner control system, an alternating current timing motor, an electric circuit including said motor and an impedance. means to close said circuit on demand for heat from the burner and to open it when said demand is satisfied, an electronic tube having its plate-cathode circuit coupled to the terminals of said motor, a switch actuated by said motor a predetermined time after it is started to start the burner, a second switch actuated by said motor at another and later predetermined time after starting of the motor tostop the burner, a phototube responsive to combustion at the burner to activate said tube and cause said motor to be stopped and held in its stopped position, whereby on failure of combustion at the burner the motor continues to turn and actuate said second switch to stop theburner.

7. In a burner control system, an alternating current motor, a clutch, a member driven in one direction from initial position by the motor through said clutch at a predetermined time rate. means for moving said member to initial position when said clutch is released. an electric circuit including said motor and an impedance, means for closing said circuit on a demand for heat from the burner to start said motor and close said clutch and for opening such circuit when said demand is satisfied to stop the motor and open said clutch, an electronic tube, a circuit including the plate and cathode of said tube and coupled to said motor, means actuated by said member a predetermined time after it is started by said motor to start the burner, means responsive to combustion at the burner to activate said tube and stop the motor and thus said member, and means to stop said burner actuated by said member on continuance of its movement in the event of failure of the combustion responsive means to stop said motor.

8. In a burner control system, an alternating current motor, a circuit therefor including an impedance comprising in series a capacitor and a resistor, a first switch to respectively close and open said circuit when there is a demand for heat irom the burner and when such demand is satisfied, a clutch, a member driven in one direction from an initial position by said motor through said clutch at a predetermined time rate. means for closing and opening the clutch respectively operable by the energization and deenergization of the timing motor, means for returning said member to initial position when said clutch is opened, an electronic tube having its plate-cathode circuit coupled to the terminals of said motor, heating means for said tube started and stopped coincidentally with the starting and stopping oi the timing motor, a phototube responsive to combustion at the burner and connected to the grid of said tube and adapted to activate said tube and stop said motor, a bias for said tube, a second switch actuated by said member a predetermined time after said motor is started to start the burner, and a third switch actuated by said member to stop the burner on continued movement of said member after failure 0! said tube to stop the motor.

9. In a burner control system, an alternating current motor, a clutch, a member driven in one direction from initial position by the motor through said clutch at a predetermined time rate, means for moving said member to initial position when said clutch is released, an electric circuit including said motor and an impedance, means ior said motor to close the last-named circuit, means 3 actuated by said member a predetermined time after the closing of the last-named circuit to start the burner, means responsive to combustion at the burner to activate said tube and stop the motor and thus said member, and means to stop said burner actuated by said member on continuance of its movement in the event 01' failure 01' the combustion responsive means to stop said I motor.

10. In a burner control system, an alternating current motor, a clutch, a member driven in one direction from an initial position by th motor through said clutch at a predetermined time rate, means for moving said member back to initial position when said clutch is released, an electric circuit including said motor and an impedance: means for closing said circuit on a demand for heat from the burner to energize said motor, close said clutch and drive said member and for opening such circuit when said demand is satisfied to deenergize the motor, open said clutch and allow said member to be moved back to its initial position by said first-named means, an electronic tube, a circuit including the plate and cathode of said tube and coupled in parallel with said motor, mean actuated by said member shortly after it is moved from said initial position by said motor to start the burner, means responsive to combustion at the burner to activate said tube and stop the motor independently of the secondnamed means and thus stop said member, means operable by continued movement of said member in said direction to a second position to stop the burner, and means for preventing return of said restored to initial position by the first-named means.

11. In a burner control system, 'an alternating current motor, a clutch, a member driven in one direction from an initial position by the motor through saidclutch at a predetermined time rate, means for moving said member back to initial position when said clutch is released, an electric circuit including said motor and an impedance; means for closing said circuit on a demand for heat from the burner to energize said motor, close said clutch and drive said member and for opening such circuit when said demand is satisfied to deenergize the motor, open said clutch and allow said member to be moved back to its initial position by said first-named means, an electronic tube, a circuit including the plate and cathode 01' said tube and coupled in parallel with said motor, means actuated by said member shortly after it is moved from said initial position by said motor to start the burner, means responsive to combustion at the burner to activate said tube and stop the motor independently of the second-named means and thus stop said member, means to stop the burner and deenergize' the motor operable by said member on continued movement in said direction to a second position in the event of failure of the combustion-responsive means to stop said motor, and means for preventing return of said member to initial position when stopped in said second position, said preventing means being manually releasable to restore said member to initial position.

12. In a burner control system, a timing memher, an alternating current motor for moving said member in one direction and capable of moving it from an initial position to a second position. means tending to move said member back tn initial position on deenergization of said motor, a circuit including said motor and an impedance, a control switch to close said circuit and start said motor and member on a demand for heat from the burner and to open the circuit when the demand for heat is satisfied and allow said member to be returned to its initial position by the first-named means, means actuated by said member after a predetermined movement in said direction from initial position to start the burner and for stopping the burner when the member -moves to its second position; an electronic tube having its plate-cathode circuit coupled in parallel with the motor, means responsive to combustion at the burner to activate said tube and cause said motor to be stopped and magnetically held in its stopped position, and means compelling retlli'nof said member to initial position be-- fore said circuit can again be closed by said switch.

13. In a burner control system, a timing member, an alternating current motor for moving said member in one direction and capable of moving it from an initial position to a second position in a predetermined time, means tending to move said member back to initial position when the motor is deenergized, a circuit including said motor and an impedance, a relay operable when energized to close said circuit, a primary control switch operable on a demand for heat from the burner to cause energization of the relay and operable when the demand is satisfied to cause deenergization of the-relay, means operable by movement of said member shortly after it is 18 moved away from initial position to start the burner and operable when the member moves into the second position to stop the burner, an electronic tube having its plate-cathode circuit connected in parallel with said motor, means responsive to combustion at the burner to activate the tube and cause the motor to be stopped and ma!- netically held in its stopped position, a pair oi contacts closed and opened when the relay is respectively energized and deenergized. a second pair of contacts connected in parallel with the first pair of contacts and closed and opened respectively when said member is in or out of initial position, the opening of both sets of contacts preventing energization or the relay, whereby when the relay is deenergized the first pair of contacts open and the second pair of contacts remain open until said member is reset to initial position.

14. In a burner control system, a single phase alternating current motor having a main field winding and a shaded pole winding for starting purposes, a circuit including said main field winding and adapted for connection to a supply of alternating current, an electronic tube having its plate-cathode circuit connected in parallel with said main field winding in the first-named circuit, a capacitor and a resistor in the first-named circuit in series with the plate-cathode circuit and with said winding and of such values as to produce resonance at the frequency of said supply and to cause the effective voltage across said terminals to be substantially greater than the effective voltage of said supply, a timing member driven away from an initial position by said motor, means for closing the first-named circuit on a demand for heat from the burner and starting said motor and for opening said circuit and deenergizing saidmotor when said demand is satisfied, means to start the burner operable after a predetermined movement or said member, means to stop the burner operable alter a further predetermined movement or said member, means responsive to combustion at e burner to activate said tube and cause said tor to be stopped and magnetically held in stopped position, and means for resetting said member to its initial position when the motor is deenergized. said tube when activated destroying the resonance of the first-named circuit and causing the eilective voltage across said terminals to drop to at least substantially that of said supply to reduce the current in the motor to a safe value during the period of operation of the burner.

15. In a burner control system, a timing member, a motor for moving said member in one direction from an initial position to a second position in a predetermined time, means tending to move said member back to initial position when the motor is deenergized, a circuit for said motor including a switch, an electromagnet for actuating said switch and operable when energized and deenergized to respectively close and open said switch to thereby open and close said circuit and energize and deenergize said motor, a primary control switch operable on a demand for heat from the burner to cause energization of said electromagnet and operable when the demand is satisfied to cause deenergization of the electromagnet, means operable by movement of said member shortly after it is moved away from initial position to start the burner, means operable when said member moves into its second position to stop the burner, means responsive to combustion at the burner to causesaid motor to be stopped and held in its stopped position, a pair of contacts closed and opened by said electromasnet when the latter is respectively energized and deenergized, and asecond pair of contacts connected in parallel with the first pair of contacts and closed and opened by said member when the latter is respectively in or out of initial position, the opening of both pairs oi. contacts at the same time preventing energization oi the electromagnet, whereby when the electromagnet is deenergized the first pair of contacts open and the second pair contacts remain open until said member is moved back to initial position.

16. In a burner control system, a timing member, a motor for moving said member in one direction from an initial position to a second position in a predetermined time, means tending to move said member back to initial position when the motor is deenergized, a circuit for said motor including a switch, an electromagnet for actuating said switch and operable when energized' and deenergized to respectively close and open said switch to thereby open and close said circuit and energize and deenersize said motor, a primary control switch operable on a. demand ior heat from the burner to cause energization of said electromagnet and operable when the demand is satisfied to cause deenergization of the electromagnet, means operable by movement of said member shortly after it is moved away from initial position to start the burner, means operable when said member moves into its second position to stop the burner, means responsive to combustion at the burner to cause saidmotor to be stopped and held in its stopped position, a pair of contacts closed and opened by said electromasnet when the latter is respectively energized and deenergized, a second pair or contacts connected in parallel with the iirst pair of contacts and closed and opened by said member when the latter is in or out of initial position, the opening of both pairs of contacts at the same time preventing energization oi the electromagnet, whereby when the electromagnet is deenergized the tirst'pair of contacts open and the second pair 01' contacts remain open until said member is moved back to initial position, and means operable when the burner is stopped by the thirdnamed means to deenergize said electromagnet.

. THEODORE J. MESH.

REFERENCES CITED The following references are oi record in the ille of this patent:

UNITED STATES PATENTS 2,263,225 Sparrow Nov. 18, 1941

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