US3432246A - Electrical flame ignition and supervising apparatus - Google Patents

Description

March 11, 1969 3,432,246

ELECTRICAL FLAME IGNITION AND S'UPERVISING APPARATUS K. J. H ALLGREEN Filed March 2, 1967 United States Patent 1) 49,515 US. Cl. 431-27 rm. c1. F23n /08 4 Claims ABSTRACT OF THE DISCLOSURE Flame ignition and supervisory apparatus for use in conjunction with a burner and a source of fuel to the burner provided with an electrical ignition element for igniting fuel discharged from the burner and monitoring the existence of a flame at the burner once the burner is ignited. Ignition control and supervisory circuitry are connected to the element to electrically energize it and render it incandescent and continually electrically energize it while flame continues to burn at the burner. The burner is disposed to monitor the flame and the control and supervisory circuitry controls an electromagnetically actuated valve controlling application of the fuel to the burner upon energization of the element and discontinuing supply of fuel to the burner when the element is deenergized in response to the absence of a flame.

This invention relates generally to gas or oil fired burner ignition and control and more particularly to electrical flame ignition and supervisory apparatus.

Combined ignition and flame supervising apparatus are known. These known devices make use of a high voltage ignition spark path which comprises an ion rectifier which carries out flame ignition and supervision and monitoring after ignition. The known apparatus, however, are relatively costly because of the necessity of using a high voltage transformer in the circuitry. Moreover, these known apparatus have a limitation in that an AC power source must be available. Furthermore, the ignition ele-. ments are rather sensitive to contamination and fouling.

The present invention has a principal object provision of a flame ignition and supervisory apparatus for igniting a flame at a burner and monitoring the fuel supply thereto by monitoring the flame.

Another object is to provide apparatus which is less expensive and more troublefree and is capable of operating with alternating or direct current.

A feature of the invention is the provision of an electrical ignition element rendered incandescent for igniting a fuel at a burner and comprising a material with a negative temperature coefiicient of electrical resistance. The ignition element is maintained in circuit with ignition circuitry and supervisory or control circuitry continuing the monitoring of a flame after ignition and turning off supply of fuel upon the absence of a flame.

The incandescent ignition element conducts an electrical current corresponding to its cold resistance when energized under control of a main switch, for example a boiler thermostat, and upon energization its resistance decreases so that within a short time current flow therethrough renders the material incandescent. So long as the ignited flame burns, a large current flows in the supervisory circuit or monitoring circuitry to which the ignition element is connected upon ignition of the fuel. Should the flame become extinguished, a current drop takes place in the supervisory circuitry due to an increase in resistance of the super- 3,432,246 Patented Mar. 11, 1969 visory ignition element and supply of fuel is cut off to the burner.

Another feature of the invention is the provision of ignition or firing circuitry for initially energizing the ignition element and controlling supply of fuel to a burner and subsequently automatically changing over to supervisory control circuitry application of current at a reduced value so long as a flame obtains at the burner. A relay is connected in the circuitry, maintaining fuel supply to the burner while energized with the reduced value of current corresponding to a holding current.

The firing and supervisory circuitry comprises a safety trip for deenergizing the ignition element after a predetermined number of ignition attempts at igniting a fuel fail. The safety trip comprises elements to protect a fuel supply motor against overcurrent or short circuiting.

Other features and advantages of the ignition and flame supervisory apparatus in accordance with the present invention will be better understood as described in the following specification and appended claims, in conjunction with the following drawings in which:

FIG. 1 is a schematic diagram of a first embodiment of ignition and supervisory apparatus in accordance with the invention; and

FIG. 2 is a second schematic diagram of a second embodiment of the apparatus in accordance with the invention.

As illustrated in the drawings, a motor driven pump 1 provides fuel, for example oil from a fuel supply source, not shown, through a discharge line 2 to an electromagnetically controlled valve 3 connected to a burner or nozzle 4 illustrated diagrammatically. The fuel is ignited at the burner which burns as a flame 5. Ignition of the fuel is carried out by an ignition and resistanc element 6 made for example in the form of a U-shaped thin rod of silicon carbide granules bonded by silicon oxy-nitride. This material is supplied, for example by Norton International Inc. under the trade name Chrystolon 63 Silicon Carbide and distributed as a refractory lining material for furnaces.

The ignition or resistance element 6 is connected across terminals 7, 8 of a 220 V. AC. main network through a first circuit comprising a main switch, for example a boiler thermostat switch 9, a movable contact 10 of a safety trip 11 and a rectifier 12 connected in series with an operating coil 13 of a relay 14 having a capacitor 15 in parallel with the operating coil 13 and in series with a movable contact 16 of the relay 14. This first described circuitry coustitutes an ignition circuit for electrically energizing the ignition element 6 to ignite the flame 5 as hereinafter described.

A second or supervisory circuit is connected to the ignition element 6 and includes the elements of the first described circuit and a shunt 17 having a variable resistor 18 connected across movable contact 16 of the relay 14.

A third supervisory circuit branch comprises a directaction heater 19 in the safety trip 11 in series with a variable resistor 20 and a second movable contact 21 of the relay 14. This last described circuit is connected to the element 6 through the relay contact 21 in series with the contact 10 of the safety trip 11 so that when the first described circuitry is energized, the relay 14 is actuated and the contact 16 opens the first circuit so current flow is through the shunt while the contact 21 closes a third set of stationary contacts closing a fourth branch circuit to the ignition element 6 through an operating coil 22 for operating the electromagnetic valve 3 and in series with an indirect-action resistor heater 23.

When the main or thermostatic switch 9 is closed, current energizes the first circuit including the relay coil 13 and the elements 6 and in the third circuit, the heater 19 and the element 6. The ignition element 6 is rendered incandescent as the current passing therethrough rises due to the decreasing resistance thereof. As soon as this current has obtained a level which renders the element 6 completely incandescent, the current corresponds to the necessary operating current level for actuating the relay 14. As the relay 14 is actuated, the current through the heater 19 is interrupted by the contact 21 and the current value through the relay coil 13 is reduced in view of the placing of the resistor 18 in the shunt 17 in circuit upon opening of the contact 16.

With the shunt in circuit the current in the relay coil 13 is suificient to act as holding current for the relay 14 but current flow is insufficient to continue to maintain the ignition element 16 incandescent. When the relay is energized, the circuit of coil 22 is closed so it is energized and the electromagnetic valve 3 is operated from a closed position to an open position so that fuel is delivered to the nozzle or burner 4 by the motor driven pump 1 which is continuously energized through the indirect action resistor heater 23 and is always in circuit with ignition and supervisory element 6 once the main switch 9 is closed.

When the valve 3 opens the ignition element is incandescent. If the fuel fails to ignite properly, the flame is extinguished and the ignition element 6 cools down to a temperature at which its inner resistance becomes sufficiently large that the current flow therethrough falls below the holding current level for relay 14 and the relay 14 drops out. When the relay drops out, the ignition circuit or first circuit is again closed and a second attempt at ignition in the above described manner takes place.

During each attempt at ignition, the heater 19, which may consist of a heating wire directly wound on a bimetal strip, generates a predetermined amount of heat and stores it, consequently the temperature and heat content thereof rise until finally the heater will open the movable contact and trip the safety trip 11. The resistor is variable and is used to set the value at which the heater 19 will trip the relay and therefore the number of ignition attempts that the ignition circuitry can attempt.

In the event that the motor driven pump 1 is overloaded, for example if it should become frozen or blocked, the second heater 23 will radiate suflicient heat to actuate the heater 19 and cause it to trip the safety trip 11 thus protecting the motor and the valve coil 22 against short circuits and the like.

The variable resistor 18 enables the holding current of relay 14 to be set at a desired value and allows adapting the characteristic parameters of the ignition element 6 to the parameters of the relay 14.

A second embodiment of apparatus in accordance with the invention is illustrated in FIG. 2 in which the elements corresponding to the apparatus in FIG. 1 have similar reference numerals. In this embodiment, the circuitry is connected substantially the same except that the electromagnetic valve 3 is replaced by an electromagnetic valve 24 operated by an operating coil 25 constituting the operating coil of a relay 26 replacing the relay 14 of the first embodiment. The relay is provided with movable contacts 27, 28 which are normally closed in a manner of the contacts 16, 21 of the relay 14. The circuitry functions in the manner of the first embodiment except that instead of a delay taking place in the opening of the fuel valve 24 as in the other valve 3 the valve 24 is immediately actuated to an open position when the operating coil 25 is electrically energized and operates the contacts 27, 28 to their open position in which current flow to the ignition element 6 is through the shunt 17.

In this instance, ignition is effected by the ignition element 6 being heated to its incandescent state by current flow through the coil 25 and the shunt 17. When the relay is energized, current flow through the element 6 is reduced by means of the resistor 18 in the shunt 17 to a value corresponding to the holding current for holding the relay 26. The safety trip 11 in this embodiment will likewise be triggered when several ignition attempts fail: to produce a flame or in the event that the motor runs with an overcurrent therein.

A number of modifications can be carried out in both embodiments without departing from the concepts of the invention. Thus, the fuel source need not comprise a motor driven pump 1 but may be, for example, a remote supply of fuel under pressure, for example a pressure gas fuel source for a gas fired burner. Moreover, the coil 22 of the electromagnetic valve may be connected without protection by the safety device or trip 11. The relays for cutting off ignition current may be provided with selfholding contacts, not shown, whose current does not pass through the ignition element 6 and may also remain permanently disconnected until reset manually.

Those skilled in the art will understand that the terminology first circuit, second circuit and third circuit etc. are terms used for ease of description and are not indicative of the number of necessary circuits for carrying out the principles of the invention.

While preferred embodiments of the invention have been shown and described, it will be understood that many modifications and changes can be made within the true spirit and scope of the invention.

What I claim and desire to be secured by Letters Patent 1. Flame ignition and supervisory apparatus for use in conjunction with a burner and a source of fuel to said burner comprising, an electrically energized ignition and supervisory resistance element for igniting fuel delivered from said burner and monitoring the presence and absence of a flame at said burner, said element having a negative temperature coefiicient of electrical resistance, circuit means comprising an ignition circuit connectable to said element energizing said element to heat it to a temperature igniting said fuel from said burner and a supervisory circuit comprising a part of said energizing circuit connect-able to said element to continue said element electrically energized during presence of said flame, said element being disposed to sense the pressure and absence of said flame, a current-responsive relay having contacts common to said ignition circuit and said supervisory circuit in series with said element for alternatively connecting said element to said ignition circuit and said supervisory circuit, an electromagnetic valve having a coil connected in said circuit means in series with said element through said contacts connected to be energized by said ignition circuit to open said valve and to retain said valve open under control of said element, a holding circuit for said relay shunting said contacts and in series with said element when said contacts open and rendered effective when said relay is energized and said. contacts open, a variable resistor in said holding circuit in series with said element when said holding circuit is rendered effective, whereby current value in said holding circuit is under control of said element and the resistance of said resistor and said relay drops out when said current drops below a selected value in response to rise of the resistance of said element above a selected value, and safety trip means common to said ignition circuit and said supervisory circuit connected to said element through said contacts effective to deenergize said coil to cut-off fuel to said burner and to deenergize said element when there has been extinguishment of said flame at said burner and in response to said element causing said relay to alternatively connect said ignition circuit and said supervisory circuit to said element without ignition of said fuel.

2. Flame ignition and supervisory apparatus, according to claim 1, in which said coil is connected common to said valve and said relay for operating said valve and said relay.

3. Flame ignition and supervisory apparatus according to claim 1, in which said relay comprises a coil in 5 6 series with the contacts of said relay rendering said hold- 2,068,425 1/ 1937 McCabe. ing circuit elfective. 2,159,658 5/ 1939 Hall 15 8 -12 4. Flame ignition and supervisory apparatus according 2,887,152 5/1959 Wilder.

to claim 1 in which said safety trip means is connected 3,209,809 10/1965 Nielsen et al.

in series with contacts of said relay other than contacts 5 3,282,324 11/1966 Romanelli 158-12( of said relay rendering said holding circuit efiective.

JAMES W. WESTHAVER, Primary Examiner. References Cited U's CL UNITED STATES PATENTS 431 66 1,745,178 1/1930 McCabe. 10

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