US3767354A

US3767354A - Oil burner control system

Info

Publication number: US3767354A
Application number: US00237415A
Authority: US
Inventors: J Wright
Original assignee: Emerson Electric Co
Current assignee: Emerson Electric Co
Priority date: 1972-03-23
Filing date: 1972-03-23
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23
Also published as: CA963556A

Abstract

A control system for fluid fuel burners including electric motor means operative to supply fuel and combustion air to a burner comprises a first circuit including a relay and a thermal time switch resistance heater completed through a conducting SCR and a space thermostat. A second circuit including the thermal time switch and a spark igniter, and a third circuit including the time switch, the electric motor windings, and a double-throw, centrifugal, motor starting switch in its start position are jointly completed through contacts of the relay when the thermostat closes. Means responsive to flame conduction cuts off SCR conduction when burner flame appears, whereby the relay opens and the resistance heater is de-energized and the igniter becomes inoperative. A fourth circuit for continued operation of the motor when the relay opens extends through the thermal time switch and is completed through the double-throw, centrifugal, starting switch in its running position, whereby the supply of fuel and air to the burner is continued so long as the burner flame persists and the thermostat is closed.

Description

United States Patent n 1 Wright Oct. 23, 1973 OIL BURNER CONTROL SYSTEM [75] Inventor: James A. Wright, Webster Groves,

[73] Assignee: Emerson Electric Co., St. Louis, Mo.

[22] Filed: Mar. 23, 1972 [21] Appl. No.: 237,415

Primary Examiner'Edward G. Favors Attorney-Charles E. Markham [57] ABSTRACT A control system for fluid fuel burners including electric motor means operative to supply fuel and combustion air to a burner comprises a first circuit including a relay and a thermal time switch resistance heater completed through a conducting SCR and a space thermostat. A second circuit including the thermal time switch and a spark igniter, and a third circuit including the time switch, the electric motor windings, and a double-throw, centrifugal, motor starting switch in its start position are jointly completed through contacts of the relay when the thermostat closes. Means responsive to flame conduction cuts off SCR conduction when burner flame appears, whereby the relay opens and the resistance heater is de-energized and the igniter becomes inoperative. A fourth circuit for continued operation of the motor when the relay opens extends through the thermal time switch and is completed through the double-throw, centrifugal, starting switch in its running position, whereby the supply of fuel and air to the burner is continued so long as the burner flame persists and the thermostat is closed.

7 Claims, 1 Drawing Figure OIL BURNER CONTROL SYSTEM This invention relates to automatic control systems for fluid fuel burners which include electric motor means operative to effect the supply of fuel and combustion air to a burner and intermittently operated ignition means which is rendered inoperative when burner flame exists. It particularly relates to means for economically achieving the intermittent operation of an igniter and is particularly adapted to, although not limited to, the automatic control of so-called blue flame oil burners and power gas burners, wherein the relatively high rate of ionization occurring in a blue flame provides greater signal conduction through the flame for reliable operation of flame conduction responsive means operative to de-energize a thermal time switch heater and ignition means when flame at the burner is established.

An object of the invention is to provid a generally new and imprpved automatic control system for fluid fuel burners including novel means to terminate operation of an igniter when burner flame is established.

A further object is to provide an automatic control system for fluid fuel burners in which an igniter is operated and fuel is supplied to the burner in the absence of flame for a predetermined short trial period under control of a thermal time switch upon starting operation of the burner, and in which igniter operation is cut off substantially instantly when burner flame is established and becomes operative substantially instantaneously if the burner flame subsequently fails.

A further object is to provide an automatic control system for fluid fuel burners in which electric motor means operative to effect the supply of fuel and air to the burner includes a double-throw, centrifugal, starting switch operative in its starting position to complete a motor starting circuit under control of a flame responsive switch and operative in its running position to complete a running circuit for the motor independent of the flame responsive switch upon establishment of burner flame.

Further objects and advantages will appear when reading the following complete description in connection with the accompanying drawing. v The single figure of the drawing is a diagrammatic illustration of a burner control system constructed in accordance with the present invention.

Referring to the drawing, the system includes a blue flame oil burner generally indicated at having an electric driving motor '12 which when operating at running speed effects the ejection of a combustible mixture of fuel and air from the nozzle end 14 of the burner. The electric driving motor 12 includes a starting winding 16, a running winding 18, and a centrifugally actuated, double-throw switch 20. The switch is normally biased in a starting position, as indicated in solid line, and is moved to a running position, as indicated in dotted line, by a conventional centrifugal actuator (not shown) when the motor attains running speed. A spark igniter 22 comprising a voltage step-up transformer having a primary winding 24, a secondary winding 26, and a pair of spaced spark electrodes 28 connected across the secondary winding 26 is operative to ignite the combustible mixture issuing from burner The motor running winding 18 is connected across

terminals

30 and 32 of an a. c. power source through circuit leads 34, 36, 38, 40, and 42, the normally open contacts 44 of a relay 46 (when they are closed), through

leads

48,50, 52, and 58, through a normally closed safety time switch 54, a lead 56, a space thermostat 60, and a lead 62. The motor starting winding 16 is connected in parallel with running winding 18 through the

leads

64 and 66, the double-throw starting switch 20 in its solid line starting position, and the lead 68. A circuit for the motor running winding 18 paralleling the relay contacts 44 is provided and includes; the lead 68, the switch 20 in its dotted line, running position, and the lead 50. The motor running winding 18 is energized, therefore, whenever the safety switch 54 and thermostat 60 are closed, and the switch 20 is in its dotted line, running position whether or not relay contacts 44 are closed.

The bimetal safety time switch 54 includes a bimetal blade 55, and an electrical resistance heater arranged (in practice) adjacent thereto is operative when energized to heat the bimetal blade sufficiently in a predetermined short period of time to cause the left free end thereof to warp upwardly away from contact 57 and therefore break the circuit at that point. The safety switch 54 is positioned so that the entire system is disconnected from the power supply when .it opens. A freely pivoted latching member 59 retains the bimetal blade 55 in a warped open switch position once it is moved there, so that its return to a closed position upon cooling requires the manual disengagement of the latch 59.

The primary winding 24 of the igniter transformer 22 is connected across the power source terminals 30-32 through

leads

34, 72, and 74, the normally open contacts 76 of the relay 46 (when they are closed), the

leads

52 and 58, the safety time switch 54, the lead 56, thermostat 60, and lead 62.

The relay 46 includes an electromagnetic winding 78 which is connected across

power source terminals

30 and 32 through the lead 34, a lead 80, the safety time switch resistance heater 70, a lead 82, a siliconcontrolled rectifier 84, the lead 58, safety switch 54, a lead 56, thermostat 60, and lead 62. An intermittent, unidirectional current therefore flows through the relay winding 78 when the thermostat is closed and the SCR 84 is conducting.- However, a diode connected across relay winding 78 in opposed polarity to SCR 84 permits some continued current flow through the winding when the SCR is cut off each half cycle, thereby retaining the filtering effect of an inductance in series with rectifier and preventing relay chattering.

A gating circuit for SCR 84 comprises a resistor 88 connected between an SCR gate lead 90 and the cathode side and

resistors

92 and 94 series connected between gate lead 90 and the anode side through a diode 96 effects conduction of SCR 84 in the absence of flame when thermostat 60 closes. A PNP transistor 98 connected between the SCR gate lead 90 and the cathode side, and having its emitter 100 connected to gate lead 90 and its collector 102'connected to the cathode side of SCR by a lead 104, is operative when conducting to shunt the application of a firing signal to SCR 84 through the described SCR gating network and thereby cut off conduction of the SCR.

The transistor 98 is preferably a Darlington amplifier comprising in effect a two-stage transistor amplifier, but for the purpose of simplifying the description and drawing, a single PNP transistor amplifier is illustrated and will function quite satisfactorily in many installations. The transistor emitter 100 is also connected to the anode side of SCR 84 through the

resistors

92 and 94 and diode 96, and its collector 102 is connected to the cathode side of the SCR in parallel with resistor 88 by the lead 104, so that the emitter 100 is positive with respect to collector 102 during the conductive half cycle of the SCR.

A resistor 106, in the order of seven megohms and being of much higher resistance than series connected

resistors

92 and 94, is connected at one end to a point between

resistors

92 and 94 and at its other end to the transistor base lead 108, and effects a lower potential at the transistor base 110 than exists at emitter 100 so that transistor 98 is forwardly biased. A capacitor 112 connected between transistor base lead 107 and the collector side charges through the high resistance 106, resistor 94, and diode 96 during the conductive half cycles of diode 96. The capacitance of capacitor 112 is such that it requires a period in the order of one second to fully charge through the described resistors. When following closure of the space thermostat 60 capacitor 112 becomes fully charged, current ceases to flow through resistor 106 while current continues to flow through

resistors

92 and 94 during the conductive half cycles, so that a higher potential now exists at the transistor base 1 than at emitter 100. Conduction of transistor 98 therefore ceases, and as a result, SCR 84 receives firing signals and becomes conductive, whereby the relay 46 closes causing a combustible mixture to be supplied to the burner nozzle, the operation of the igniter, and the energization of safety switch resistance heater 70.

A conductive probe 114 is positioned adjacent the nozzle 14 of the burner 10 in a position to be impinged by burner flame when the burner is operating normally. The burner 10 is constructed of electrically conductive material and is grounded at 116. The system is also grounded at 118 near terminal 30, so that when a normal flame exists at burner 10, a discharge path for capacitor 112 is provided extending from transistor base lead 108 through the resistor 80, lead 82, the probe 1 14, and through the burner flame to ground during the non-conductive half cycle of diode 96 when supply terminal'32 is positive. The discharging of capacitor 112 through the burner flame at a greater rate than it can be charged through high resistance 106 will again result in a partially or fully discharged capacitor and, consequently, a voltage drop across resistor 106 which will re-establish the forward biasing and conduction of transistor 98 and, consequently, the cutoff of SCR 84.

A small capacitor 120, connected in parallel with resistor 88 between the SCR gate lead 90 and the cathode side, operates to damp any high frequency pulses which may result from switching at thermostat 100, or from other causes, and which may otherwise momentarily fire the SCR, upon starting, before the capacitor 112 is fully charged to permit the application of a firing signal to the SCR. This premature firing of the SCR would cause objectional clicking or chattering of the relay 46. Such momentary firing of the SCR may also otherwise occur when the thermostat opens at a time when the SCR is normally not conducting.

OPERATION gating of SCR 84. The capacitor 112 is, however, now

charging through the high resistance 106 and resistance 94 during the conductive half cycles of diode 96. There being no burner flame at this time to provide a discharge path during alternate half cycles, the capacitor 112 becomes fully charged in the order of one second. When this occurs conduction through transistor 98 is cut off and SCR 84 becomes conductive.

When SCR 84 conducts the safety switch resistance heater and the relay 46 are energized and

relay contacts

44 and 76 close. Closure of relay contacts 76 ef fects operation of the igniter 22 and closure of contacts 44 completes a circuit for the motor to effect the supply of a combustible mixture to the burner nozzle. A timed trial period during which fuel, air, and ignition are supplied is therefore initiated. Upon closure of the relay contacts 44, the circuit for the motor starting winding 16 is completed through the starting switch 20 in its solid line, starting position. When the motor attains running speed to supply a combustible mixture, starting switch 20 moves to its dotted line, running position, thereby de-energizing the starting winding 16 and completing a circuit for the running winding 18 which circumvents the relay contacts 44. It will be understood that motor-driven power burners are conventionally arranged to provide a combustible mixture to the nozzle only after the motor has attained running speed.

When, under normal conditions, combustion occurs at the burner nozzle 14 within the trial period determined by resistance heater 70, a discharge path for capacitor 112 through the burner flame is provided. Only a very small flow of current through the flame is required to discharge the capacitor 112 at a greater rate than it can be charged through the high resistance 106. Discharging of capacitor 1 12 through the burner flame results in a voltage drop across high resistance 106 and a drop in potential at transistor base 110, and transistor 98 now conducts, thereby shunting the application of a firing signal to SCR 84 and thereby cutting off conduction.

When conduction through SCR 84 is cut off in response to the appearance of burner flame, the safety switch heater 70 and relay 46 are de-energized and

relay contacts

44 and 76 open. De-energization of resistance heater 70 renders the'safety switch 54 inoperative to terminate the trail period. Opening of relay contacts 76 cuts off operation of the igniter 22; opening of relay contacts 44 does not, however, cut off operation of the motor 12 because the starting switch 20, in its dotted line, running position, completes a circuit for the motor running winding around these relay contacts. The motor and therefore the burner will now continue to operate until the thermostat 60 is satisfied and opens.

If, upon starting, combustion fails to occur within the predetermined trail period, the resistance heater 70 will cause the bimetal safety switch 54 to warp open and remain latched open, thereby cutting off operation of the entire system. To re-start burner operation under these conditions, the latch 59 is manually released to permit bimetal blade 55 to reclose with contact 57.

In combustion fails for any reason during normal operation, conduction of transistor 98 will be cut ofi and conduction of SCR 84 will be resumed. Operation of the igniter and energization of the safety switch resistance heater 70 will therefore be resumed substantially instantaneously upon flame failure, and the opening of safety switch 54 will occur in a short predetermined period of time unless flame is re-established within this period.

If the electrical power supply fails during normal burner operation, the centrifugally actuated motor switch will return from its dotted line, running position to its solid line, starting position, thereby cutting off motor operation due to the fact that relay contacts 44 will be open under these conditions. Re-starting the motor will therefore require the closure of relay contacts 44 and energization of relay 46 and the series connected safety switch heater 70. Energization of the realy will also effect operation of igniter 22, so that if the electrical power supply is interrupted during burner operation, the burner motor will only be re-started upon resumption of power supply through energization of the relay and the safety switch heater, and with igniter 22 in operation.

I claim:

1. In a burner control system, an electrical power source, ignition means, a space thermostat, a burner including an electric motor operative at running speed to supply a combustible mixture to the burner nozzle, said motor including starting and running windings and a double-throw centrifugal starting switch normally connecting said windings in parallel, a relay having a winding and normally open contacts, and a normally closed thermal time switch; circuit connections connecting said motor windings across said power source through said thermal time switch and through said relay contacts and said space thermostat when they are closed; and circuit connections including said doublethrow starting switch when in a running position connecting said motor running winding across said power source through said thermal timev switch, and said thermostat independent of said relay contacts; an electrical resistance heater operative when energized to open said thermal time switch in a predetermined short period of time, and normally conductive switching means; circuit connections series connecting said relay winding and said resistance heater across said power source through said normally conductive switching means and said thermostat; and flame resonsive means operative to cut off conduction through said normally conductive switching means when burner flame appears.

2. The burner control system claimed in claim 1 in which said ignition means is electrically operated and which further includes circuit connections connecting said ignition means across said power source through said relay contacts when they are closed.

3. The burner control system claimed in claim 2 in which said normally conductive switching means comprises a solid state switch including gating means normally biasing it conductive, and in which said flame responsive means is operative in response to electrical conduction through the burner flame to render said gating means inoperative, whereby operation of said igniter is cut off substantially instantaneously when burner flame appears and is restored to operation substantially instantaneously if the burner flame is subsequently extinguished.

4. In a burner control system, an electrical power source, a space thermostat, a burner including electric motor-driven means operative to supply a combustible mixture, said motor including running and starting windings, a double-throw centrifugal starting switch, ignition means, a normally closed time switch, and a resistance heater operative when energized to open said time switch in a short time; circuit means including said resistance heater operative when said thermostat closes to connect said motor windings across said power source through said thermal time switch; circuit connections including said starting switch in a running position connecting said motor running windings across said power source through said thermao time switch and said thermostat; and said circuit means further including flame responsive switching means operative to render said circuit means inoperative when combustion occurs.

5. The control system claimed in claim 4 in which said ignition means is electrically operated and in which said circuit means is further operative to connect said ignition means across said power source through said thermal time switch.

6. The burner control system claimed in claim 4 in which the burner is a blue flame oil burner, and in which said flame responsive switching means comprises a controlled solid state switch including gating means normally operative in the absence of burner flame to render said switch conductive, and means including amplifying means responsive to signal conduction through the burner flame to render said gating means inoperative and cut off conduction of said switching means.

7. In a burner control system of the kind described, an electrical power source, an electrically operated igniter, a burner, a burner motor having starting and running windings and a double-throw centrifugal starting switch, a space thermostat, a thermal time switch, and a resistance heater operative to open said time switch in a short time; first circuit means including relay means and said resistance heater operative to connect said igniter and both motor windings across said power source through said time switch and said thermostat when said motor starting switch is in a start position; second circuit means connecting said motor running winding across said power source through said time switch and said thermostat when said motor starting switch is in a running position; and said first circuit means further including normally conductive switching means responsive to flame at said burner to render said first circuit means inoperative.

Claims

1. In a burner control system, an electrical power source, ignition means, a space thermostat, a burner including an electric motor operative at running speed to supply a combustible mixture to the burner nozzle, said motor including starting and running windings and a double-throw centrifugal starting switch normally connecting said windings in parallel, a relay having a winding and normally open contacts, and a normally closed thermal time switch; circuit connections connecting said motor windings across said power source through said thermal time switch and through said relay contacts and said space thermostat when they are closed; and circuit connections including said double-throw starting switch when in a running position connecting said motor running winding across said power source through said thermal time switch, and said thermostat independent of said relay contacts; an electrical resistance heater operative when energized to open said thermal time switch in a predetermined short period of time, and normally conductive switching means; circuit connections series connecting said relay winding and said resistance heater across said power source through said normally conductive switching means and said thermostat; and flame responsive means operative to cut off conduction through said normally conductive switching means when burner flame appears.

4. In a burner control system, an electrical power source, a space thermostat, a burner including electric motor-driven means operative to supply a combustible mixture, said motor including running and starting windings, a double-throw centrifugal starting switch, ignition means, a normally closed time switch, and a resistance heater operative when energized to open said time switch in a short time; circuit means including said resistance heater operative when said thermostat closes to connect said motor windings across said power source through said thermal time switch; circuit connections including said starting switch in a running position connecting said motor running windings across said power source through said thermal time switch and said thermostat; and said circuit means further including flame responsive switching means operative to render said circuit means inoperative when combustion occurs.