US3064719A

US3064719A - Fuel burner control apparatus

Info

Publication number: US3064719A
Application number: US82421A
Authority: US
Inventors: Graves Donald Lee
Original assignee: Electronics Corp of America
Current assignee: Electronics Corp of America
Priority date: 1961-01-13
Filing date: 1961-01-13
Publication date: 1962-11-20
Anticipated expiration: 1979-11-20
Also published as: DE1401938A1; CH403138A; AT241005B

Description

Nov. 20, 1962 D. L. GRAVES FUEL BURNER CONTROL APPARATUS Filed Jan. 13, 1961 NGI mOZOOm-m Z- 20F/FOI INS- F Ill INVENTORS D.L. GRAVES BY L MS Y ATTORNEY 3,064,719 FUEL BURNER CONTROL APPARATUS Donald Lee Graves, Woburn, Mass., assigner to Electronics Corporation of America, Cambridge, Mass., a corporation of Massachusetts Filed Jan. 13, 1961, Ser. No. 82,421 8 Claims. (Cl. 158-23) This invention relates to an apparatus for the safe automatic lighting of a fuel burner and for its safe shutdown in the event of either ignition or flame failure.

Fully automatic industrial furnaces burning oil or gas employ either spark electrodes or a pilot burner to ignite the main iburner. A pilot burner, if used, is ordinarily ignited by spark electrodes. The heating period is initiated by the closing of contacts in a thermostat or similar control. In order to put the burner into operation at the beginning of each heating period, the ignition and fuel supply systems must be turned on in a proper sequence. This is frequently accomplished by a programming relay or an automatic timer which closes and opens contacts in the control circuits at predetermined intervals. The entire starting operation is known as the starting cycle. On a typical burner, the iburner motor is first turned on. The ignition follows. If a pilot is used, the pilot valve is opened at the same time. After a certain interval, during which the ignition or pilot llame is established, the main fuel valve is opened. After another interval, during which the main llame becomes established, the ignition is turned olf, leaving the burner in normal running condition. When the space or vessel to be heated reaches the desired temperature, the contacts of the thermostat open, shutting down the burner. When the thermostat contacts close again, the starting cycle is repeated. Because of the explosion hazard associated with an industrial furnace of large capacity, a llame detector is usually provided to shut down the burner in case of failure of the main llame or the pilot, in order to prevent the accumulation of unburned fuel in the combustion chamber.

Flame detectors are of various types and respond to such flame characteristics as llame conduction or radiation. In order to provide a high degree of safety, the operating condition of the llame detector and control circuit is generally checked prior to the starting cycle to determine whether or not `burner operation can he safely initiated. This is usually accomplished by applying to the control circuit a simulated flame signal which serves to operate the circuit in a normal manner. If the control circuit does not function properly on the simulated llame signal, then the control apparatus is safely held inoperative.

It is the principal object of this invention to obtain a fuel burner control apparatus which offers a high degree of safety and Versatility with a minimum number of switching members.

Other and incidental objects of this invention will be apparent to those skilled in the art from a reading of this specification and an inspection of the accompanying drawing in which:

FIGURE 1 shows a circuit diagram of a fuel burner control apparatus in accordance with this invention, and

FIGURE 2 is a time chart showing the sequence and relative duration of the closing of the contacts of the timer used in the circuit of FIGURE 1.

Referring now to 'FIGURE l, there is shown a transformer 11 having a primary Winding 13, and

secondary windings

15, 17 and 19. One terminal 21 of the primary winding 13 is connected to the ungrounded side of an A.C. power line, while the other terminal 23 of the primary winding 15 is connected to the grounded side of the power line. There is also shown another transformer United States atent G 6 3,04,719 Patented Nov. 20, 1962 25 having a primary winding 27 and a secondary winding 29.

Terminal 21 is connected through the timer switches 31 33, and 35 to the timer motor 37 yback to ground. Terminal 21 is also connected through timer switch 39, the starting interlock switch 41, the limit switches 43, and

timer switches

45, 47, and 49 through the main fuel Valve 51 to ground. Starting interlock switch 41 must be closed before the burner can be started. It is designed to allow the fburner to start only when a given condition, which must be met for starting purposes only, has lbeen met. For instance, it may be a switch which opens when the oil temperature falls below a certain minimum level. Or, in a burner having two independently controlled fuel nozzles, with an igniting electrode near the r.first nozzle only, it may be a switch which is closed only when the second nozzle is inoperative. The switch 41 may be either open or closed after operation has begun. The junction 53 of

timer switches

45 and 47 is connected through the llame relay switch `55 to a point 59 which itself is connected to the junction 60 of

timer switches

47 and 49, to the ungrounded side 62 of the ignition circuit 61 through the time switch 63, and optionally to ground through terminal 64 of an intermittent ignition or 0ptional burner motor connection 65. Junction 67 of the limit switches 43 and of the timer switch 45 is connected through thermal lock-out switch contacts 69 and 71 to the ungrounded terminal 73 of transformer winding 27, or through thermal lock-out

switch contacts

69 and 75 through the alarm 77 back to ground. The junction 79 of the starting interlock switch 41 and of the limit switches 43 is connected through the control relay switch 81 to the control relay switch contact 83 and to the junction 85 of

timer contacts

31 and 33. Junction S5 is-con nected to ground through the burner motor 87. The control relay switch comprising contact S3 is a single pole double-throw switch which connects contact 83 either to contact 89 which is itself connected to terminal 21, or to contact 91 which is connected to the timer motor 37,. The timer switch 35 is shunted by the flame relay switch 93.

The llame detection portion of the fuel fburner control apparatus comprises flame sensing means such as photocell 95 or flame rod 97. Serially connected resistors 99 and 101 are connected in shunt with the photocell 95. The anode 103 of photocell 95 is connected to the tap 105 on transformer winding 17 through a capacitor 107. The junction 109 of resistors 99 and 101 is connected to the control grid 111 of triode 113. The cathode 115 of triode 113 is connected to ground, and its anode 117 is connected lto the terminal 119 of secondary winding 15, the other terminal 121 of which is connected to the control grid 123 of triode 125. The control grid 111 is connected to ground through serially connected capacitor 127 and resistor 129. The control grid V123 is connected to ground through resistor which is shunted by serially connected capacitor 131 and resistor 133. The cathode 137 of triode 125 is connected to ground, and the anode 139 of triode 125 is connected to the ungrounded terminal 141 of transformer winding 17 through the llame relay 143. The llame relay 143 is shunted by a capacitor 145. The heaters 147 and 149 of

triodes

113 and 125 are supplied from the secondary winding 19 of transformer 11.

l 'The junction 151 of capacitor 127 and resistor 129 is connected through timer switch 153 and through the operating control switch 155 to the terminal 159 of transformer winding 29. The junction 161 of capacitor 131 and resistor 133 is connected through contact 163 of the single-pole double-throw llame relay switch and through timer contact 167 to one terminal 169 of the control relay 171. The other terminal 173 of control relay conducting state.

' Operation The operation of the system shown in FIGURE'I will be described for an oil burner with an interrupted gas pilot. llt will lbe assumed that a source of power, usually 120 volts, single phase A.C. is present at

input terminals

21 and 23. It will also be assumed, initially, thatthe system previously underwent a complete starting cycle, that operating control switch 1'5'5 is open,'and that timer 37 is in the starting position, as shown in FIGURE 2.

Normal Starting Cycle Transformer 11 is energized by the power supplied to

input terminals

21 and 23, thereby providing power for filaments 147 and 149 which are connected to winding 19. Transformer 25 is simultaneously energized through 'timer contact 39, starting interlock switch 41, limit switches 43, and the thermal lock-out switch 69, the operation of which will be described hereinafter. The 131.-C. voltage appearing at tap 105 of winding 17 is coupled to the yllame detecting circuit through the capacitor 107. The flame detecting circuit comprises either the flame rod 97 or the photocell 95 which is used to detect Visually the main llame. The unidirectional current which ows through capacitor 107 as a result of the rectifying elements in the ame detecting circuit serves to prouduce a net negative charge on the plate of capacitor 107 `connected to llame rod 97. The voltage appearing-across the capacitor 107, then, is referred to the grid and cathods of tube 113 through isolating resistor 99 and through nthe portion of secondary winding 17.

The grid 111 of tube 113 is biased negatively with respect to the cathode 115 and this bias voltage, developed 'when a'anie is detected or when a checking signal is applied, is -sufficient to Vdrive tube 113 to cutoff. When 'tube`11`3 is biased to cutoff and is non-conducting, no bias voltage is 'developed across resistor 135 and tube 125 is thus able to conduct. Capacitor 145, which is connected in shunt with relay 143, stores sufficient energy during the half cycles when tube 125 is conducting to keep relay 143 energized during the half cycle when tube 125 is not conducting. vIn this manner, a bias voltage developed across capacitor 107 by the ame detector drives tube 113 to cutoff .and Vthus allows tube 125 to conduct and enerlg'ize relay'1'43. Y

When -tube 113 is not biased to cutoi, a current flows during positive half cycles from tap `119 of transformer 11 through tube 113 back to tap 121k of transformer V11 through lthe -parallel paths of resistor 135 and serially Yconnected-resistor 133 and capacitor 131. The direction t of currentflow is such as to produce a voltage drop across Y the same time that the plate of tube 125 is positive and'is thus suicient to drive tube 125 to cutoff. `Conventional polarity transformer markings are shown on the windings of transformers llvand 25. It is therefore vevident that relay k143 is Vde-energized whenever tube 113 is in the Upon need for burner operation, operating control switch 155 is closed either Ymanually or by means of a -thermostatic control. For checking purposes, a flame signalis ."simulated.' This occurs whenever operating control l'switch 155 and timer contact 153 are closed. The

secondary windings of Ytransformers 11 and 25 are so rrelated in phase that tap 159 of transformer 25 is positive -when tap 119 of transformer 1/1 is negative; Whenthe voltage. 31125311.59 is positiveand the'voltageon plate 117 of tube 113 is negative, a current flows from tap 159 Vof transformer 25 through capacitor 127 and the grid-cathode path yof tube 113 to ground back through resistor 177 to tapV 175 of secondary winding 29. In the alternate half-cycle when the voltage at tap 159 is negative, and the voltage at tap 119 is positive, tube 113 is held cutoff as a result of the net voltage appearing across capacitor 127. The charge that leaks off capacitor 127 during this alternate half-cycle through resistors 101 and 129 is negligible. When tube 113 is held cutoff, tube 125 is permitted to conduct, thereby energizing relay 143.

When relay 143 is energized, relay 171 is simultaneously energized by the power supplied by secondary winding 29 through tne resulting path comprising timer contact 167 and contact 185 of relay switch 165 and operating control switch 155. When relay 171 is energized, burner motor 87 is energized through contact 89 of relay switch 83. Timer motor 37 is also energized through contact 89 of relay switch 83 and timer switches 33 and 35.Y The timer contact 181 closes providing a current path through the parallel combination of heater 179 of the thermal lock-out switch 69 and

closed contacts

185 and 167. The charge on vcapacitor 127 leaks off through resistors 101 and 129 subsequent to the opening of contact 153. This discharge time constant is chosen so that after about one second, a ysufficient amount of charge has leaked olf capacitor 127 to permit tube 113 to conduct, thereby cutting 'off tube 125 and de-energizing relay 143. However, before relay 143 is deenergized and, infact, after six seconds of timer rotation, timer contact 167 opens, thereby removing the 'shunt current path around heater .179.

Heater 179 thus conducts current andbegins to heat up.

After nine seconds of time rotation, timer contact v35 opens but does not interrupt power applied to timer motor 37 since contact 35 is shorted by relay switch 93. Y Contact 35 recloses after twelve -seconds of timer rotation and thus precludes subsequent interruption of power to timer motor 37 by the opening of switch 93. At the,vv

same time, timer contact 63 closes'but does not affect the circuit. Timer contact 45 closes after 15 seconds/lof time rotation andthu's energizes the ignition circuit;t 61 'through contacts 47 Vand 63, which ignition circuit includes the ignition transformer and the pilot fuel vs'i'alve. With the burner motor `87 and the ignition circuit 61Y in the energized state, a pilot ame is established.

The pilot llame that -is initiated causes a unidirectional current to ow through capacitor 107 from tap 105 of 'secondary winding 17.V As previously described, tube 113 is cut olf and tube 125 conducts, thereby energizing relay V143. After 25 seconds of timer rotation, contact167 recloses, completing through contact Y185 of relay-switch 165 a shunt path around the lock-out switch heater 17,9 which thus stops heating. At the same time, contact 47 Since relay 143 is enerpower lines through

timer contacts

45 and 49 and switch 55. The'ignition circuit 61, however, `remains energized whenrcontact 47 opens because of the shunt pathprovided by relay switch 55. The main-ilameis thus estab- Vlished and is detected by the Vame detecting element or 97.

If the conduction of tube reduces to theY point where relay 143 is de-energized after 25 seconds of timer rotation, i.e., when flame-is required to be detected, then tube'125 Vwill beheld in the non-conductive state.

InV

describing the safety feature of the present invention that is apparent at this time, it should be pointed out that operating control 155,

timer contacts

167 and 181 are closed, that timer contact 153 is open, and that contact 185 is connected to switch 165. If flame signal ceases or diminishes sufficiently to let tube 113 conduct, and the conduction of tube 125 reduces to the point where relay 143 will not be energized, switch 165 will break from contact 185 and connect to contact 163. On the half cycles where the voltage applied to plate 139 and the voltage at tap 175 are negative, a current tlows through the heater 179 and through timer contact 167 to the junction 161 of resistor 133 and capacitor 131. Current ow during this half-cycle is such as to produce a voltage across capacitor 131 that is of proper polarity to bias tube 125 negatively. Thus, when the plate voltage of tube 125 becomes positive in successive half-cycle, the tube will have suiiicient negative bias voltage between grid 123 and cathode 137 to maintain tube 125 cut-olf. By this process, relay 143 is prevented from being energized if it assumes a de-energized position during any part of the burner starting cycle after contact 167 closes at 25 seconds of timer rotation.

The pilot flame is extinguished after 35 seconds of timer rotation as a result of timer contact 63 opening. However, relay 143 is maintained in the energized state as a result of the continued detection of the main flame. After 45 seconds of timer operation timer contact 33 opens and de-energizes timer motor 37. There is no further switching action until the operation control switch 155 opens as a result of information provided by the temperature of the headed space or vessel.

Normal Shutdown When the heat demand is satised the operating control switch 155 is opened either manually or by the thermostatic control. This de-energizes relay 171. The circuit through contact 89 and switch 81 is broken and connection to contact 91 is thus made. The burner motor S7 remains energized through contact 31. The main fuel valve 51 and the optional burner motor connection 65 are de-energized by the opening of relay switch 81, and the timer motor 37 is re-energized through timer contact 31 and contact 91 of relay switch 83. No effect is produced upon the circuit when

timer contacts

45 and 49 open and contact 47 closes after fty seconds of timer rotation. Also, no effect i is produced on the circuit when

contacts

153 and 33 close and contact 181 opens after 55 seconds of timer rotation.

After sixty seconds of timer rotation, contact 31 opens and de-energizes the burner motor and timer motor. At the same time, contact 39 closes but has no eiect at this time.

rThe timer now has made one complete revolution and is again in the starting position. When the starting interlockiswitch 41, limit switches 43, and operating control switch 155 are again actuated simultaneously, a repeat of the cycle just described will result.

Several other modes of operation are possible using the circuit of the present invention for various combinations of main flame fuel and igniting means. By way of example, and to demonstrate the versatility of the present invention, operation of the circuit for a few of the possible fuel and ignition means combinations will be described hereinafter.

Operation for Gas Burner With Intermittent Gas Pilot The ignition circuit 61 is connected as shown. A pilot valve control is connected in the position of block 65. The sequence of operation is the same as in the normal operating sequence with the exception that pilot valve control 65 is not de-energized after 35 seconds of timer rotation, but rather remains energized for as long as the main fuel valve 51 is energized. A failure of the main ame will not de-energize the fuel valve 51 if the pilot ame remains burning and detected.

Operation fOr Oil Burner With Interrupted Spark Ignition The ignition circuit 61 and main fuel valve 51 are connected as shown and a jumper connecting terminal 50 and terminal 64 is provided. The operation of the circuit is the same as described for the normal starting cycle until after 15 seconds of timer rotation. Contact 45 closes, completing a circuit from terminal 67 to i-gnition circuit 61 through contact 47 and contact 63 and completing a circuit from terminal 67 to the main fuel valve 51 through contact 47 and the jumper between terminals 5t) and 64. With burner motor 87, ignition circuit 61, and main fuel valve 51, now all energized, a flame is established. When the main flame is sensed, the signal thus developed causes tube to conduct, thereby energizing relay 143. Contact 167 closes after 25 seconds of timer rotation, thus providing a shunt current path around heater 179 through contact of switch 165, which heater thus stops heating. At the same time, contact 47 opens and contact 49 closes but this does not affect the circuit operation at this time because of the shunt path provided by relay switch 55. After 35 seconds, contact 63 opens, thus de-energizing ignition circuit 61. The operation of the circuit is substantially the same as the operation described for the normal starting cycle after contact 33 opens at 45 seconds of timer rotation. i

Operation Following POwer Interruption During Normal Starting Cycle If power is interrupted prior to the opening of contact 39 at a time three seconds after the start, normal sequence of operation proceeds when the power is resumed. However, if power is interrupted after three seconds of timer rotation when contact 39 opens and contact 31 closes, relay 171 cannot be re-energized when power is resumed because of contact 39 and switch 81 both being open. The burner motor 87 will be re-energized through contact 31 and timer motor 37 will also be re-energized through contact 31 and contact 91 of switch 83 when power is resumed. Both motors will remain energized until contact 31 opens at time 60 seconds and no other loads will be energized during this period because of the aforementioned open state of both contact 39 and switch 81.

Operation for False Flame Signal During Checking Period The operation of the circuit progresses as a normal starting cycle up through the opening of contact 153 at time live seconds after starting. Although the checking signal is then removed, relay 143 remains energized because of real or simulated signal at that time. Contact 167 opens at time six seconds and current flows through heater 179 which subsequently begins to warm up. Contact 35 opens at time nine seconds and the timer motor is thus de-energized because switch 93 is also open. After about one minute, the heated bimetallic element of the lockout switch 69 detiects from contact 71, thereby de-energizing transformer 25 which thus de-energizes relay 171. Blower motor 87 remains energized through contact 31 and timer motor 37 is re-energized through contact 31 and contact 91. Both motors now remain energized until contact 31 opens at time 60 seconds. No other loads will be energized during this period because both contact 39 and switch 81 are open. When contact 39 closes at time 60 seconds, power is again applied through contact 39, starting interlock switch 41 and limit switches 43 to junction 67. However, since lockout switch 69 is not connected to contact 71, transformer 25 cannot be energized. There can be no further burner operation until lockout switch 69 is manually reactuated to its normal position.

Operation for Flame Failure or Loss of Detection After Contact 47 Opens The operation of the circuit is the same as the operation for the normal starting cycle until the main flame is established and is detected by the photocell. However, if

insufii'cient llame signal is developed as a result of loss of ame or other factors, relay 143 becomes dez-energized. There can be no Afurther power applied to ignition circuit 61 and main fuel valve 51 because both contact 47 and switch 55 are open. Heater 179 begins to heat up because contact 185 no longer provides a shunt current path. Lockout will occur about one minute after contact 185 is opened, thereby causing relay 171 to become cle-energized. Timer motor 37 will then become re-energized through contact 31 and switch contact 91, and Will advance through the cycle until both timer motor 37 and blower motor 87 are de-energized by the opening of contact 31 at time 60 seconds. When lockout occurs, alarm 77 is energized until switch 69 is manually reactuated to its normal position.

Therefore, the circuit of thepresent invention provides many safety features which are readily apparent to those skilled in the art. Some of the safety features provided are:

(1) A precise ignition trial period of a short, safe duration which is not affected by normal variations of line voltageor ambient temperature.

(2) A check, prior to ignition period, of the ability of the iiame responsive relay to pull in with signal and` to drop out when there is no signal. This check is eiective whether or not the ampliiier is operating at the time burner operation is called for and cannot be adventitiously circumvented,

(3) A lockout in the event a'false signal is prolonged for a minute or more during safety check to avoid danger of initiating another firing cycle,

(4) An optional pre-purge period to clear the furnace of unburned gases,

(5) A post-purge period to sustain combustion air while a slow-operating gas Valve is closing,

(6) Non-recycling of the operation following ignition, ame, o r component failure, and

(7) A cut-off of the flame-responsive relay current following a tiame failure to avoidvpossibility of re-energizing the main fuel valve without ignition Abeingpresent during lock-out procedure.

. It should be noted also that-several circuit simplifications are provided by the system design of the presentinvention. For example, the location of starting interlock circuits permits starting andre-'setting switches 39 and 31 to be combined as a single-pole double-throw switch. The circuit arrangement also permits a two-pole control relay 171 with one single-throw and one double-throw contact to initiate burner motor operation, to initiate timer 'motor operation, to provide a maintaining circuit around the starting interlock circuit, and to interrupt power applied to ignition and fuel valve Vloads and to its own actuator vwhen such action is required. This permits economical relay design and circuit design since oneside of the control relay contacts are electrically common toeach other,

` control switch to be actuated'upon the need for `fuel burner operation, a timer having a motor and a plurality of switches controlled thereby, flame sensing means, a arne relay connected tothe output of said-flame sensing means including the first switch of said flame relay in the energizedlstate and a second timer switch to energize said control relay, means including the iirst switch of said control relay in its energized state and a third timer switch to energize said timer motor, means responsive to the opera-V tion of said timer motor to open said second timer switch, means including the second switch of said control relay for maintaining said control relay in its energized state, means responsive to `the operation of said timer motor to remove said checking signal and deenergize said ame relay, means responsive to the further operation of said timer motor to open said third timer switch, means including the second switch of -said flame relay in its deenergized state for maintaining said timer motor in its energized state, and means including a fourth timer switch responsive to the further operation of said timer motor to actuate said ignition means.

2. A programming apparatus according to claim l including means responsive to the further operation of said timer motor to deenergize said timer motor.

3. A programming apparatus according to claim 2 yfurther comprising means including a fth timer switch and the lirst switch of said control relay in its deenergized state to energize again said timer motor and reset it toits starting position.

4. A programming apparatus according to claim 3 further comprising means including the second switch of -said control relay in its deenergized state to .prevent energization of said ignition means and main fuel valve while said timer is resetting.

5. A programming apparatus according to claim 3 Vand further comprising a thermally actuated lockout device comprising a heating element serially connected with said control relay and a lockout switch actuated thereby, a sixth timer switch andthe first switch of said'ame relay in its energized state being'serially connected to provide an electrical path shunting said heating element. l

6. A programming apparatus according to claim 5 wherein said heating element is energized upon 'the opening of said shunt path, and wherein the energization of said heating element beyond aV predetermined time 'inter-val causes the lockout switch actuated thereby to deenergize -said control relay.

burner operation, a timer having a motor and a plurality 4 of switches controlled thereby, ame sensing means, a ame relay connectedto the output of said flame sensing means and having an energized state indicative 4'of the presence of flame and a deenergized state indica 've of the absence of flame, said flame relay having'an actuator and iirst and second switchescontrolled therebyf'a control relay having an energized state indicative of the need for and having an energized state indicative of the presence of flame and a deenergized state indicative of the absence of llame, said flame relay having an actuator and first and second switches controlled thereby, a control relay having .burnereoperationand a first timer switch to generate a checkingsignal to .simulate the presence of 'flame and thereby causeV the energization of said flame relay, means fuel burner 'operation and a deenergized state indicative of no need Vfor fuel burner operation, said control relay having an actuator and lirst and second switchesfcontrolled thereby, means including said operating control switch and a first timer switch to generate a checking signal to simulate the presence of ilame and thereby cause-the energizav tion of said ame relay, means including the first switch sof said lame relay VAin the energized vstate and a'second timer switch to energizesaid control relay, means includ-y .ing the rst switch of said control relay in its energized ing signal and deenergize said flame relay, means respon- References Cited in the le of this patent sive to the further operation of said timer motor to open said third timer switch, means including the second switch UNITED STATES PATENTS of said flame relay in its deenergized state for maintaining 2 616 490 Wilson et al Nov. 4, 1952 said timer motor in its energized state, and means inelud- 5 2748845 Marshall et a1 June 5 1956 ing a fourth timer switch responsive to the further opera- 2966940 Graves et a1 Jan 3 1961 -tion of said timer motor to actuate said ignition means.