US3327193A

US3327193A - Control apparatus for burner systems

Info

Publication number: US3327193A
Application number: US429245A
Authority: US
Inventors: Mungard Hans
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1964-02-05
Filing date: 1965-02-01
Publication date: 1967-06-20
Anticipated expiration: 1984-06-20
Also published as: NL6501428A; GB1031623A; BE658949A; DE1279884B

Description

June 20, 1967 H. MUNGARD 3,327,193

CONTROL APPARATUS FOR BURNER SYSTEMS Filed Feb. 1, 1965 United States Patent 8 Claims. oi. 318-421) The present invention relates to control arrangements for fuel burners utilizing a single phase AC fuel supply motor, and further containing a flame sensitive element to indicate the absence or presence of a flame, particularly for use in oil burners.

Single phase AC motors having separate starting windings require that the starting winding be disconnected when the motor comes up to running-speed. This disconnect mechanism is often incorporated with the motor itself, sensing the speed of the motor, and disconnecting the starting Winding when a predetermined speed is reached.

It is an object of the present invention to decrease the number of parts necessary in a control system for an AC motor having sensing elements to determine the presence or absence of a flame.

In accordance with the present invention, the starting relay, sensitive only to the speed of the motor itself, can be omitted, when a flame sensitive element isused, if the flame sensitive element is so arranged that it will disconnect the starting winding of the motor when a flame is sensed, that is that the flame sensitive element controls the starting circuit of the motor itself.

A flame sensitive element is usually provided in all oil burner installations as a safety means. When a thermostatic control requires more heat, the motor is started and oil is transported into the combustion chamber. An

ignition device, known in the art, is provided to ignite the oil. Should there be any failure, for some reason or another, of ignition, then considerable damage may result if oil is being pumped into the combustion chamber which is not burned. To prevent such damage, photosensitive switches were provided to disconnect the ignition device, and to stop the oil supply motor. Additionally, an alarm signal may be given.

According to the present invention, the photo-sensitive switch is further utilized to interrupt the starting of the motor; this is based on the realization that, when a flame is present, the motor must be running. Conversely, the flame can be expected as soon as the motor has come up to speed.

The safety function of this photo-switch is in no way changed by the arrangement according to the present invention. It is desirable to include in the starting winding a time delay relay, such as a hot wire relay, which disconnects the motor entirely in case the photo-sensitive switch should become defective and not indicate the presence of a flame. Also, should the oil supply become defective so that the motor does not reach its running speed and so that, therefore, no oil is pumped and no flame results, the motor will be disconnected thus avoiding damage thereto. In case the flame should go out, although the motor is still running, the photo-switch will react, and shortly thereafter, the time delay safety switch will again open the main circuit to the motor. Of course, current will have flowed for some period of time through the starting winding. This will not cause damage to the motor, however, when it is disconnected shortly thereafter.

In its simplest form, the heating winding of a hot wi-re relay is merely placed in series with the photoswitch and the starting winding of the motor. This also provides for protection to the motor in case the hot wire of the heating relay should burn out.

Electric motors usually tolerate a good deal of overload for a limited period of time. If the dimensioning of the motor is not such that it will remain below its temperature limit when the running winding is subjected to excessive loading, for example due to unexpected trouble in the oil supply line, a positive temperature coeflicient resistance can be placed in series with the motor running winding, or other motor protective devices known in the art can be used in conjunction therewith.

In order to decrease the number of movable parts, and particularly the number of mechanically operating relays, it is particularly desirable to use solid state devices. Solid state switching elements which change their resistance value from that of a high resistance to one of low resistance value, when a predetermined sensing threshold voltage is exceeded, have been found particularly useful. Such devices may be, for example, m-ulti-layer diodes.

A particularly interesting device for use in connection with solid state switch elements useful in the invention is made from telluri-um, with additives taken from Groups IV and V of the periodic table of elements. The base substance is polycrystalline. These switches are absolutely symmetrical, have high current carrying capacity, and are easily manufactured. Their switching threshold potential can readily be changed by choice of the relative ratio of components, or by appropriate choice of the thickness of the body. As an example, a solid state switch may consist of approximately 67.5% tellurium, 25% arsenic and 7.5% germanium, made by evaporation on a metal plate, by sintering, or by solidification of an alloy melt.

A pair, or more, of such solid state switch elements can be arranged as a single unit having a common electrode. Each of the elements can be switched separately; yet a combined assembly is entirely possible, simplifying the connection to the common terminal, or junction, over that of several physically separate elements.

A pair of such solid state switching elements are connected in series. These elements have the characteristic that they change their resistance from that of a high resistance value, in the order of up to several megohms to one of low resistance value in the order of an ohm or less when a predetermined switching threshold voltage connected thereacross, is exceeded. The switching threshold voltage of each element is chosen to be greater than half of the line voltage. Thus, since the line voltage is less than the switching threshold voltage of the element, in series, they will both remain in their high value of resistance, or switched OFF condition. A trigger potential, which is greater than the switching threshold voltage of one of the elements, but which may be less than the line voltage, is then applied across one of the elements only. Upon application of this switching potential, the element across which it is applied, will change to its low resistance, conducting condition, and remain in the conducting condition until the current through the element drops to almost zero. Almost full line voltage will thus be applied to the other element which will also switch and change its condition to low resistance, thus completing a low resistance circuit through both elements, and switching the entire series circuit ON.

The structure, organization, and operation of the invention will now be described more specifically in the following detailed description with reference to the accompanying drawings, in which:

FIG. 1 is a typical voltage (abscissa) vs. current (ordinate) diagram for solid state switching elements for use in the switch according to the present invention; and

FIG. 2 is a schematic circuit diagram of the control arrangement according to the present invention.

FIG. 1 shows, diagrammatically, a current I through a symmetrical solid state switching element, having a voltage U applied thereacross. Below the threshold potential :U the current is practically Zero since the element is in its high resistance state, in which its resistance is up to several megohms (curve I). As soon as the switch ing threshold potential U is exceeded, the switching element changes to its low resistance state (curve 11), in which its resistance may be one ohm or less. The current through the switch is then essentially determined only by the resistance of the remainder of the circuit. The element remains in the low resistance state until the current therethr-ough decreases below the holding value J which is almost at the zero point. As soon as J is passed, the element changes back to its high resistance state.

Five layer diodes or other multi-layer diodes with an odd number of layers show this characteristic. The best results, however, have not been obtained with multi-layer diodes, but with the polycrystalline solid state switching element consisting essentially of tellurium with the additives previously mentioned.

Referring now to FIG. 2, a control circuit for use-With an oil burner is illustrated. Control unit 1 is connected to a single phase alternating current supply connected to lines U and O, of which may be grounded. An oil burner motor 2, having running winding 3 and starting winding 4, control thermostat 5, shown schematically as a switch, safety photo-resistor 6, and ignition transformer 7 with ignition electrodes 8, are indicated schematically, and connected to the control unit 1. All these components are well known in the field. The control equipment itself has a safety switch 9 which, when it is connected from its normal position as shown, to the alarm position, causes an alarm signal lamp 10 to light. A starting and safety circuit may be traced from line U through switch 9', running winding 4 of motor 2 to line 0. Another circuit extends from line U, switches 9 and 5 to a junction of a resistor 12 and, in parallel with the resistance 12, and a low resistance heat sensitive relay 11; and solid state switch unit 13, formed of two serially connected switch elements 14 and 15, applied to a common electrode 17. The switch B effectively places in circuit or takes out of circuit the star-ting winding 4. The elements 14, 15, are deemed as two single, separate solid state switch elements as indicated by the dashed line 16. Unit 14 is connected to relay 11. The electrode 17 is connected to a junction 18, formed by the resistor 12, and a photo-resistor 15. Photoresistor 6 has the resistor similar to that of resistance 12 when illuminated, but a substantially higher resistance value than resistor 12 when dark. The switch element and the other terminal of photoresistance 6 are connected to the starting winding 4 of motor 2, the other terminal of which is connected to line 0.

The operation of this circuit is as follows: When thermostatically controlled switch 5 closes, line potential is applied over closed switch 9, to the running winding 3 of the motor 2, to the ignition transformer 7 and to the starting circuit. The current through solid state device 13 is extremely low, because the device 13 is, initially, in its high resistance condition and thus, practically, presents an open circuit. Additionally, current will flow through resistor 12, photo-sensitive resistor 6 and starting winding 4. This current is insuflicient to start the motor. However, as stated before, the resistance of photo-sensitive resistor 6, when dark, is substantially higher than that of the resistor 12. Thus, the major portion of the voltage drop from the line supply U, 0, will occur over photosensitive resistor 6, and will be applied over element 15 of the solid state device 13, by the connection from junction 1 8 to the common electrode 17 The path 15 of solid state device 13 will thus have a potential applied which is greater than its switching threshold potential, and switch to its low resistance state. As soon as this happens, substantially the entire line voltage will be applied across the solid state resistor 12, that is also across element 14, thus causing switching of the entire device 13 to its low resistance condition. Current through the starting circuit and starting winding 4 will now be suflicient to cause the motor 2 to start. If the flame lights, the resistance of photo-sensitive resistor 6 will drop and become substantially equal to the resistance of resistor 12. At the next half cycle the device 13 will then switch over into its high resistance state. As soon as the flame is lit, however, the motor has already come up to sufl'icient running speed so that power is no longer necessary for the starting winding. In case the flame should not light, however, the starting current will cause temperature sensitive resistance relay 11 to heat, causing switch-over of switch 9 from the position shown, opening the circuit from line U through the motor, thus stopping motor 2 supplying fuel to the burner. Also, line U will be connected to alarm light 10. Preferably, the switch 9 is arranged in such a manner that it will lock in position keeping the lamp 1t} lit until manually reset to the position illustrated in the drawing.

Short circuit at the photo-sensitive resistor 6 does not cause a dangerous condition. In such case, full potential is applied across the resistor 12, and then first the region or element 14 of the solid state device 13 will switch to the low resistance condition; thereafter or element region 15 will switch to the low resistance condition. Since there will be no disconnection of the starting winding, current will flow over heating element 11 for an unduly long time, which will again cause operation of safety switch 9 and an alarm. A similar operation will result in case photo-sensitive resistor 6 should burn out. In such case, element 15 of the solid state 13 will switch first, then element 14, and the device or switch 13 will remain in its low resistance condition, again causing operation of the heating coil 11 and safety switch 9.

The circuit is very economical in its use of components and parts; and inherent fail-safe, regardless of malfunction of the flame sensitive device.

It is to be noted that the solid state switching device not only disconnects the starting winding during ordinary running condition, but furthermore controls the safety disconnect in case there is malfunction in the system. The solid state switch 13 is easily controlled, for example by the photo-sensitive resistor 6, thus providing for a savings in components in parts while maintaining the electrical requirements as well as safety requirements of the system.

I claim:

1. A control arrangement for a single phase AC fuel supply motor having a running winding and a starting winding; flame sensitive sensing means sensing the presence or absence of a flame, said sensing means having a first resistance value when a flame is present, and a second resistance value when a flame is absent; and a starting and safety circuit in series with said starting winding, said starting and safety circuit including a pairof serially connected voltage sensitive elements having a common junction and which change their resistance from a high resistance value to a low resistance value when a predetermined switching threshold voltage connected thereacross is exceeded; means for applying said switching threshold voltage to said elements comprising said flame sensitive sensing means and a resistor having a value of resistance similar to said first resistance value; means connecting said resistor and flame sensing means in series circuit, and means connecting said series circuit being connected across said pair of voltage sensitive elements; a cross connection from the common junction between said resistor and said flame sensing means to the common junction of said pair of voltage sensitive elements.

2. A control arrangement according to claim 1, including a time delay safety relay responsive to a predetermined current for a predetermined time, said time delay relay being connected in said starting and safety circuit.

3. A control arrangement according to claim 1, said pair of serially connected voltage sensitive elements comprise a single unit on a common substrate, said common substrate defining said common junction between said pair of elements.

4. A control arrangement according to claim 1, said voltage sensitive elements comprising two regions of a polycrystalline body consisting essentially of tellurium, with additives of elements of Groups IV and V of the Periodic Table of Elements.

5. Control apparatus for a single phase AC motor having a running winding and a starting winding comprising, connections for connecting said apparatus to a voltage source including connections connecting said motor and said control apparatus and connections for said motor to said voltage source, photo-resistor means sensing the presence or absence of a flame, said photo-resistor means having a first resistance value when a flame is sensed thereby and a second resistance value in the absence of a flame, switch means connected to said starting winding and to said photo-resistor means comprising voltage-responsive means having a high resistance state changeable to a low resistance state when a predetermined switching threshold voltage connected thereacross is exceeded, means including said photo-resistor means for applying in operation said switching threshold voltage to said switch means and effective to cause said photo-resistor means to cooperate with said switch means to effectively change said switch means to said high resistance state thereby to effectively deenergize said starting winding when a flame is sensed.

6. Control apparatus according to claim 5, including ignition means for igniting a fuel in operation to cause said flame, means connecting said ignition means to said connections for energization thereof when said driving winding is energized.

7. Control apparatus according to claim 6, including means to stop said motor in the event said ignition means is ineffective to ignite said fuel.

8. Control apparatus according to claim 7, in which said means to stop said motor comprises a thermally-responsive relay in series with said switch means disconnecting said switch means and said starting winding and said driving winding from said connections connecting said motor to said voltage source.

References Cited UNITED STATES PATENTS 2,420,578 5/1947 Wilson 318-471X 2,449,858 9/1948 Ottmar 31s 471 x 3,116,445 12/1963 Wright 31s 22o 3,263,158 7/1966 Bargen et al. 31s 473 X 3,273,626 9/1966 Brown 318221 x ORIS L. RADER, Primary Examiner.

G. Z. RUBINSON, Assistant Examiner.

Claims

1. A CONTROL ARRANGEMENT FOR A SINGLE PHASE AC FUEL SUPPLY MOTOR HAVING A RUNNING WINDING AND A STARTING WINDING; FLAME SENSITIVE SENSING MEANS SENSING THE PRESENCE OR ABSENCE OF A FLAME, SAID SENSING MEANS HAVING A FIRST RESISTANCE VALUE WHEN A FLAME IS PRESENT, AND A SECOND RESISTANCE VALUE WHEN A FLAME IS ABSENT; AND A STARTING AND SAFETY CIRCUIT IN SERIES WITH SAID STARTING WINDING, SAID STARTING AND SAFETY CIRCUIT INCLUDING A PAIR OF SERIALLY CONNECTED VOLTAGE SENSITIVE ELEMENTS HAVING A COMMON JUNCTION AND WHICH CHANGE THEIR RESISTANCE FROM A HIGH RESISITANCE VALUE TO A LOW RESISTANCE VALUE WHEN A PREDETERMINED SWITCHING THRESHOLD VOLTAGE CONNECTED THEREACROSS IS EXCEEDED; MEANS FOR APPLYING SAID SWITCHING THRESHOLD VOLTAGE TO SAID ELEMENTS COMPRISING SAID FLAME SENSITIVE SENSING MEANS AND A RESISTOR HAVING A VALUE OF RESISTANCE SIMILAR TO SAID FIRST RESISTANCE VALUE; MEANS CONNECTING SAID RESISTOR AND FLAME SENSING MEANS IN SERIES CIRCUIT, AND MEANS CONNECTING SAID SERIES CIRCUIT BEING CONNECTED ACROSS SAID PAIR OF VOLTAGE SENSITIVE ELEMENTS; A CROSS CONNECTION FROM THE COMMON JUNCTION BETWEEN SAID RESISTOR AND SAID FLAME SENSING MEANS TO THE COMMON JUNCTION OF SAID PAIR OF VOLTAGE SENSITIVE ELEMENTS.