US3434788A

US3434788A - Burner control system

Info

Publication number: US3434788A
Application number: US675200A
Authority: US
Inventors: James A Wright
Original assignee: Emerson Electric Co
Current assignee: Emerson Electric Co
Priority date: 1967-10-13
Filing date: 1967-10-13
Publication date: 1969-03-25
Anticipated expiration: 1986-03-25

Description

March 25, 1969 J. A. WRIGHT BURNER CONTROL SYSTEM Filed 061;. 1a, 1967 N VEN 7'02 JAMES A WEIGHT J) 444 ZM United States Patent US. Cl. 431-66 4 Claims ABSTRACT OF THE DISCLOSURE A gas burner control system having an electrically energized glow coil igniter positioned so as to be im pinged by burner flame and a photoconductive sensor which is insensitive to gas flame but is responsive to radiant energy of the glow coil when it is at ignition temperature to effect the flow of gas to the burner and to reduce the electrical energization level of the coil, and in which a sumcient glow coil temperature is maintained at the reduced electrical energization level due to its being positioned in the burner flame to effect a continued response of the sensor which will maintain the flow of gas to the burner.

An object of the invention is to provide a simple and reliable safety control system for gas burners employing a metallic, electrical resistance, glow coil igniter which is electrically energized to ignition temperature only until ignition of the gas occurs and is thereafter during burner operation energized to a lesser degree in order to extend the life of the coil.

A further object is to provide an arrangement in which the electric current flow through a fuel control relay electrically connected in series with a photoconductive cell varies with the temperature of an electrically energized igniter glow coil which activates the cell, in which the igniter coil is initially electrically energized to gas ignition temperature to ignite the burner and to effect suflicient conduction through the photoconductive cell and relay to cause the relay to close to a fuel supplying position, and in which the temperature of the igniter coil is reducedupon closure of the relay by reducing its electrical energization level to that which will activate suflicient conduction through the photoconductive cell and relay to hold the relay closed but not sufficient to move the relay closed from an open position.

A further object is to provide an arrangement as in the foregoing paragraph in which the igniter coil is positioned in the burner flame, in which the electrical energization level of the igniter coil is reduced upon closure of the relay to a level below that which will heat the coil sufliciently to hold the relay closed, and in which heating of the coil by the burner flame raises its temperature to that which will activate suflicient conduction through the photoconductive cell and relay to hold the relay closed whereby a flame failure will result in opening of the relay.

A further object is to provide an arrangement as set forth in the two preceding paragraphs in which the igniter glow coil is constructed of a material such as platinum which catalyzes combustion of the gas, and in which catalytic action as well as heating of the igniter coil by the burner flame supplements the resistance heating of the glow coil to provide a temperature thereof which will activate the photocell to conduction which is suflicient to hold the relay closed but is insufficient to close it.

Other objects and advantages of the invention will appear from the following description when read in connection with the accompanying drawing.

FIG. 1 of the drawing is a schematic diagram of a gas burner control system constructed in accordance with the present invention;

FIG. 2 is a side elevational view of the control relay and its switching construction.

Referring to the drawing, a gas burner is indicated at 10 to which gas is supplied from a suitable source through conduit 12. A normally closed solenoid valve 14 having a winding 15 is interposed in conduit 12 and controls the flow of gas to the burner 10. The burner 10 is ignited by a platinum or platinum alloy glow coil igniter 16. The glow coil igniter is positioned in the path of gas issuing from the burner 10 and is impinged by flame when the burner is ignited. Low voltage current is supplied to glow coil 16 by a voltage step-down transformer 20 having a secondary winding 22 and a primary winding 24.

Other primary elements of the system are: a photoconductive sensing device 26, a relay generally indicated at 28 having a winding 30, a switch blade 32 and a contact 36, a current limiting resistor 37, a heating resistor 38, a bimetal switch 39 having a contact 4.1, a fuse 40, a thermostat 42, a double-throw manual switch 44, and a pair of terminals 46 and 48 for connection to a commercial power source.

The photoconductive sensing device 26 is a cadmium sulphite, solid state device directed so as to be activated by radiant energy from glow coil 16. The device 26 has extremely high resistance to the flow of electrical current when inactivated by [radiant energy and becomes sufliciently conductive for the purposes to be described when the glow coil igniter is heated to predetermined temperatures. Inasmuch as the frequency response curve of a cadmium sulphite sensing cell peaks in the infrared band and falls to zero in the yellow band, activation of the cell by radiant energy from an efficiently operating blue flame gas burner is negligible.

The relay 28, shown in FIG. 2, is biased in the deenergized open position, as shown in FIG; 2, by a spring 35. In this open position switch blade 32 is open with respect to contact 36. When winding 30 is sufficiently energized the blade 32 moves to a closed position with contact 36, as shown in dotted line. The relay 28 being biased open with its clapper 32 spaced from its core 33, it requires a higher value of energization of winding 30 (more current flow) to effect its closing to the dotted position than is required to hold it in this closed position with the clapper 32 against core 33. The relay may, therefore, be held in the closed dotted line position at a lower energization value of coil 30 than is required to move it to a closed position.

This ditferential in the required energization value of winding 30 between closing and holding closed the relay is further increased by the provision of a permanent magnet 53 which cooperates with an armature 55 carried by switch blade 32 to provide a slight additional force holding the relay closed. The additional holding force provided by permanent magnet 53 requires a still further reduction in the current flow through relay winding 30 to permit biasing spring 35 to move blade 32 to its open position.

The relay winding 30 is connected across the power supply terminals 46 and 48 in series with the double-throw manual switch 44, the thermostat 42, the photoconductive cell 26, and the fuse 40, by

leads

52, 54, 56, 58, 60, 62, and 64.

The primary winding 24 of ignition transformer 20 is connected across the power supply terminals 46 and 48 in series with switch 44, thermostat 42, and normally closed bimetal switch 39, by

leads

52, 54, 56, 65, 67, 69, 72, and 64. The ignition transformer primary winding 24 is also connected across the bimetal switch 39 through a resistor 37 by the leads 75 and 76.

The resistor 38, in heat transfer relationship with bimetal switch 39, is connected across the power supply terminals in series with the manual switch 44, thermostat 42, the switch blade 32 and contact 36, by

leads

52, 54, 56, 66, 71, 73, 74, and 64. When the resistor 38 is energized, it causes the bimetal switch 39 to warp open with respect to its contact 41 in a relatively short time, as in the order of two or three seconds.

The solenoid valve winding is connected across the power supply terminals in series with manual switch 44, thermostat 42, relay switch blade 32 and contact 36 by

leads

52, 54, 56, 66, 71, 68, 70, and 64.

The photoconductive cell 26 is also connected across the power supply terminals 4648 in series with fuse 40 through the hot side (dotted line) of thermostat 42 and the open side (solid line) position of double-throw manual switch 44 by

leads

52, 54 or 57, 78, 58, 69, and 64.

OPERATION When it is desired to operate the burner, the doublethrow manual switch 44 is moved from its open solid line position shown to its closed dotted line position. The closing of switch 44 completes the circuit connecting ignition transformer primary winding 24 across the power supply terminals 46-48 through the thermostat 42 (in its cold position shown) and through bimetal switch 39. The transformer primary winding 24 is now connected directly across the power supply and the glow coil 16 being fully energized to a high level quickly heats to ignition temperature. The photoconductive cell 26 is activated to a high level of conductivity by the glow coil and effects the pull in of relay 28 causing the switch blade 32 to close with contact 36.

When relay switch blade 32 closes with contact 36 the described circuit through winding 15 of the normally closed solenoid valve 14 is completed, causing the valve to open and gas to flow from burner 10 to be ignited by glow coil 16. The closing of relay blade and contact 32- 36 also connects the heating resistor 38 across the power supply, and after a short period of two or three seconds, the resistor 38 causes bimetal blade 39 to warp away from its contact 41, thereby limiting the flow of current through transformer primary 24 to that permitted by current limiting resistor 37. This reduction in current flow through primary 24 by resistor 37 reduces the temperature of glow coil 16 to that which, in the absence of a burner flame, is insufficient to activate photoconductive cell 26 to a conductivity which will hold the relay in its closed dotted line position.

In normal operation burner flame occurs within one or two seconds after the closing of relay 28 and the energization of the solenoid valve, so that flame is now impinging the glow coil. The burner flame, together with catalytic action of the platium coil, raises the temperature of the glow coil 16 sufficiently above that to which it is energized through resistor 37 to effect a conduction through the sensing device 26 and relay winding 30 which will hold the relay 28 open. The temperature which the coil will attain when its energization is limited by resistor 37 will not, however, even with the supplementary heating or shrouding of the flame and catalysis, approach that necessary to effect a conduction through cell 26 which will pull in relay 28. It will be noted that after the relay is closed in normal operation, and until resistor 38 heats bimetal switch 39 sufficiently to open it, the glow coil 16 will be energized to ignition temperature. When the thermostat is satisfied during normal burner operation and moves to its hot dotted line position, the igniter will be completely disconnected.

The fuse 40 is calibrated to burn out at a slightly higher current flow than that required to effect the pull in of relay 28 so that if the photocell 26 breaks down and becomes conductive at any time when manual switch 44 is open or the thermostat is in its hot position, the relay 28 will not be pulled in. The photocell being connected across the power source terminals in series with the fuse 40 through the manual switch 44 when open (solid line position), and through the manual switch 44 and thermostat 42 when the manual switch is closed (dotted line position) and the thermostat 42 is in its hot (dotted line) position, a failure of the photocell during inoperation of the burner will effect a burn out of fuse 40 and prevent subsequent pull in of relay 28 when switch 44 is closed and thermostat 42 moves to a cold demand position.

If the photoconductive cell becomes faulty during burner operation and becomes abnormally conductive, it may not burn out the fuse due to the impedance of relay coil 30, but as soon as the thermostat is satisfied and moves to its dotted line position, the photocell and fuse will be directly connected across the power source and the fuse will be caused to burn out, thereby preventing a reopening of valve 14 upon subsequent closure of the thermostat.

I claim:

1. In a burner control system, a burner, a source of electrical power, a normally closed fuel valve, an electric glow coil igniter, circuit means connecting said igniter across said power source effecting the heating thereof to ignition temperature, a relay including a winding, said relay having a biased open position and an energized closed position to which it moves when its winding is fully energized, a photoconductive cell, circuit means connecting said photoconductive cell and said relay winding in series relationship across said power source, said photoconductive cell being responsive to the radiant energy of said glow coil and becoming sufficiently conductive when said glow coil is at ignition temperature to permit full energization of said series connected relay winding and effect the closing of said relay, means rendered operative when said relay closes to effect the opening of said normally closed fuel valve, and means rendered operative when said relay closes to effect a reduction in current flow through said glow coil, and therefore its temperature, to that which will effect a conductivity of said photocond-uctive cell sufficient to hold said relay closed but less than that required to close it.

2. A burner control system as set forth in claim 1 in which said glow coil is constructed of a material which catalyses the combustion of the fuel, in which said glow coil is positioned so as to be in the path of the fuel issuing from said burner and impinged by burner flame, and in which the heating of the glow coil by the reduced electrical current flow therethrough, and the heating by catalysis and burner flame, maintains a temperature thereof which activates said photoconductive cell to conductivity suflicient to hold said relay closed but insufficient to close If.

3. A burner control system as set forth in claim 1 in which said relay includes detent means rendered operative upon closure of said relay to require a greater reduction in current flow through said relay winding to permit its return from its closed position to its biased open position.

4. A burner control system as set forth in claim 1 in which said circuit means connecting said glow coil across said power source includes a normally closed heat opened bimetal switch, and a current dropping resistor connected 5 across said bimetal switch, and in which said means rendered operative upon closure of said relay to effect a reduction in current flow through said glow coil comprises a resistance heater for heating said bimetal switch and circuit connections completed upon closure of said relay 1O connecting said resistance heater across said power source.

6 References Cited UNITED STATES PATENTS 3/1963 Wright et a1. 431-66 10/1964 Matthews 431-66 X FREDERICK L. MA'ITESON, JR., Primary Examiner. ROBERT A. DUA, Assistant Examiner.

US. Cl. X.R. 431-70