US3673464A - Energization system with safety provision for faulty rectifier - Google Patents

Abstract

A fail-safe spark ignition system for gas burners includes a spark energy monitoring circuit for controlling the gas valve and bimetal spark gap disabling means for eliminating radio interference. Two circuit arrangements are shown for protection against short circuit failure of rectifiers energizing the gasvalve solenoid or other load from an AC power source, using a second rectifier and a fuse or fusible resistor for circuit disconnection.

Description

United States Patent Lamb et al. 1 June 27, 1972 54 ENERGIZATION SYSTEM WITH 2,693,566 11 1954 Hooper .317/43 SAFETY PROVISION FOR FAULTY 3,423,666 l/1969 Brown ..317/43 RECTIFIER 3,480,374 11/1969 Lamb etal ..317 43 2,813,243 11 1957 Christian et al ..321 12 Inventors: John T. Lamb, Mansfield; Carl L.

son, Shilon, both of Ohio Assignee:

Filed: Oct. 7, 1970 Appl. No.: 78,825

Related US. Application Data Ander- The Tappan Company, Mansfield, Ohio Continuation-impart of Ser. Nos. 754,304, Aug. 21, 1968, and Ser. No. 841,200, July 14, 1969, which is a division of Ser. N01 651,865, July 7, 1967.

US. Cl ..317/43, 317/52, Int. Cl Field of Search...

References Cited UNITED STATES PATENTS Bedford ..H02m l/l8, H02h 7/10 ...H02h/3/l8; 317/42, 52; 321/1 1,

Primary ExaminerL. T. Hix Attorney-Oberlin, Maky, Donnelly and Renner [5 7] ABSTRACT A fail-safe spark ignition system for gas burners includes a spark energy monitoring circuit for controlling the gas valve and bimetal spark gap disabling means for eliminating radio interference. Two circuit arrangements are shown for protection against short circuit failure of rectifiers energizing the gas-valve solenoid or other load from an AC power source, using a second rectifier and a fuse or fusible resistor for circuit disconnection.

3 Claims, 3 Drawing Figures PATENTEDJum I972 CO NT ROL K m P s izov INVENTORS. JOHN 7. LAMB SPARK IGNITOR BY wmwmayam CARL L. ANDERSON ATTORNEYS ENERGIZATION SYSTEM WITH SAFETY PROVISION FOR FAULTY RECTIFIER This application is a continuation-in-part of applications Ser. No. 754,304, filed Aug. 21, 1968, entitled Electric Self- Cleaning Oven Circuit," and Ser. No. 841,200, filed July 14, 1969, entitled Energization System With Safety Provision for Faulty Rectifier"; the latter being a division of application Ser. No. 651,865, filed July 7, 1967, entitled Spark Ignition System.

The problem of devising a system for igniting the various burners including the oven burner in a cooking range has seen several solutions. Predominant among these is the use of a pilot light which remains burning at all times in close proximity to each of the burners to that when the has valve is turned on, the gas willflow near the flame of the pilot light to ignite the burner. Failure of these devices is sometimes monitored by a thermostatic element which is energized by the heat of the pilot light and which serves to prevent the flow of gas to the burner in the event of the absence of the pilot light flame. Such ignition systems, of course, are wasteful of gases in that a continuous flame is required even during idle times of the range with the subsequent rapid deterioration of burner ports and the like, and also present the danger of having an open flame at the range.

Glow type igniter elements have also been utilized to provide a sufficiently high temperature in the area of the combustible gases. However, these devices are subject to frequent burnout and in addition, require auxiliary means to detect when there is a failure of the element.

The spark ignition system circumvents many of the faults of previous systems in that the spark mechanism need only be energized when the appropriate valve for the burner is turned on and additionally, is not subject to wear or breakdown as is common in the earlier systems. In the spark ignition system, however, it isstill desired to know whether some extraneous material has somehow faulted the spark gap or whether the ignition system itself is producing sufficient spark to ignite the gases. Furthermore it is desirable, in order to prevent outside interference from the energy radiated from the spark gap, to extinguish the spark when it is determined that the appropriate burner has ignited.

Therefore, it is an object of this invention to provide an improved spark ignition system which is more reliable than previous systems and includes means for extinguishing the spark when the burner has lighted.

It is another object of this invention to provide an improved spark ignition system which monitors the intensity of the sparks occurring at the gaps and prevents the flow of gas if there is insufficient or nospark available.

It is still another object of this invention to provide an improved spark ignition system which detects faults within the components of the system itself and prevents flow of gas to the burners.

It is yet another object of this invention to provide safety apparatus for protecting any load energized from an AC source of power against short circuit failure of a power rectifier.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, the following description and the annexed drawing setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

IN SAID ANNEXED DMWING:

FIG. 1 is a schematic representation of a range burner system with a spark ignition system;

FIG. 2 is a circuit schematic of the spark ignition system, including a first embodiment of rectifier safety circuit; and

FIG. 3 is a circuit schematic of a second embodiment of rectifier safety circuit.

A typical range burner system is shown in FIG. 1 and consists of an input gas line 10 leading to a burner 12. Such burner 12 might comprise a surface cooking unit of a range or the oven burner and may take the configuration of 'a greater number of burners since the teachings of this invention are applicable to all such embodiments. Interposed in the input gas line 10 prior to the burner 12 is a manually operated gas valve 14 for controlling flow of gas to the burner 12. The valve 14 includes an electrical switch 16 connected to the spark control system 18 by the lines 20 such that opening of the valve 14 to allow flow of gas to the burner 12 closes the switch to actuate the spark control 18.

Also interposed in the input gas line 10 leading to the burner 12 is an electromagnetic gas valve 22 which in this embodiment of the invention is located on the input side of the manual valve 14. In a multiple burner system the electromagnetic valve controls the flow of gas to all burners and the valve would be responsive to actuation by the spark control system which would provide the spark ignition at all burners.

A single spark gap 24 is shown in proximity with the burner 12 of the range, however, it will be appreciated that the teachings of this invention apply as well to multiple gap arrangements, either in single or in plural burner ranges. The gaps are located in close association with each of the burners in such a position as to be in proximity to the flow of unburned gases emanating from the respective burner. The spark gap 24 consists of a pair of electrodes 25 separated a small distance and retained in position by a ceramic insulating block 26 which may be mounted to the range. Electrical leads 27, 28 lead to to the spark control and carry voltage sufficient for arcing to the gap 24.

The spark control 18 includes a spark igniter 30 shown in box form which is representative of any type of ignition producing device which generates adequate voltage for arcing across the gap 24 of the burner 12. In a simple form such spark igniter 30 may be merely a transformer which converts ordinary household voltage to voltage suitable for the production of an arc across the gap 24.

It will be apparent, then, that the following operation of the spark ignition system is desired. When the manual valve 14 is turned on in order to light the burner 12, the spark igniter 30 is energized to create sparks across the gap 24 associated with the burner 12. Recognition of the occurrence of adequate sparking will cause the electromagnetic valve 22 to be actuated to allow the flow of gas into the burner 12. If for any reason insufiicient sparking occurs at the gap 24, the electromagnetic valve 22 will be deenergized, thereby shutting off the flow of gas into the burner 12.

In the circuitry for the spark ignition system ordinary household voltage as a typical supply of power is applied on lines 32 to the spark igniter 30 and on lines 34 to the circuitry for controlling the electromagnetic valve 22. The switch 16 associated with the manually operated gas valve 14 is shown in association with the spark igniter 30 and it will be understood that closure of the switch 16 will energize the spark igniter 30 to cause a sufficient voltage to be applied at the output terminals 34, 35. The spark gap 24 is connected in series together with a capacitor 36 across the output terminals 34, 35 of the spark igniter 30, terminal 35 of the spark igniter 30 being connected also to the chassis ground of the range. Connected across the capacitor 36 are a resistor 38 and neon lamp 40 in series, which provide a means for monitoring the energy at the spark gap 24.

Thus, in operation when a spark of the correct energy is developed by the spark igniter 30 and appears across the spark gap 24, such spark current will cause a charge to occur across the capacitor 36. The capacitor 36 is provided to accumulate the spark energy and holds enough charge between sparks to maintain the neon lamp 40 in a lit condition. The flow of current through the resistor 38 and the neon lamp 40 will, of course, tend to discharge the capacitor 36 and by a proper selection of components, the discharge time of this circuit may be adjusted so as to maintain the neon lamp 40 in a lit condition only when sufficient energy is provided. A resistor 42 or rheostat (shown in dotted lines) may be connected in parallel across the capacitor 36 to vary the discharge time of the circuit and adjust the circuit for desired spark conditions.

In the electromagnetic valve circuit, household voltage is applied on lines 34 to the electromagnetic valve which is connected in series with a fuse 44 and an amplifier circuit 46 for providing a flow of current through the valve 22. The amplifier circuit 46 provides the energization for the electromagnetic valve 22 and in this embodiment is a silicon controlled rectifier 48 having its anode connected to one side of the electromagnetic valve 22 and its cathode connected to one of the input lines 34. The SCR 48 is poled to conduct current flow through the electromagnetic valve 22 in the forward direction as indicated by the arrow when the SCR 48 is triggered into conduction. As is typical in devices of this type, current flow occurs on alternate half cycles of the applied alternating current input voltage. A diode 50 is connected in parallel across the electromagnetic valve 22 having its anode connected to the anode of the SCR 48 and its cathode connected to the junction between the fuse 44 and the electromagnetic valve 22, thereby being poled to conduct reverse current flow in a direction opposite to that indicated by the arrow. Thus, in the normal operation of the electromagnetic valve circuit, the diode 50 will have no effect upon the current passing through the electromagnetic valve 22 since the diode 50 is back biased and exhibits a high resistance.

A triggering network for the SCR 48 consists of a photoelectric device 52 and a resistor 54 which are connected in series between the anode and cathode of the SCR 48. The common junction 56 between the resistor 54 and the photoelectric device 52 is connected to the gate lead of the SCR 48 and produces the voltage for triggering the SCR 48 into conduction. The type of photoelectric device 52 is not critical to this invention since it is only necessary that it alter the bias of the SCR 48 and this may be accomplished if the device 52 provides a high resistance when no light is falling upon it and a substantially lower resistance when it receives light from the neon lamp 40. Thus, the photoelectric device 52 and resistor 54 act as a voltage divider, taking a proportion of the voltage applied across the SCR 48 to be applied to the gate lead of the SCR 48. When little or no light is falling upon the photoelectric device 52, the high resistance will provide insufficient voltage at the junction 56 and at the gate lead to the SCR 48 to cause triggering of the SCR 48. When a sufiicient amount of light falls upon the photoelectric device 52, a greater proportion of the voltage applied across the SCR 48 will appear at the junction 56 and by suitable selection of the photoelectric device 52 and the resistor 54, may be made sufficient to cause conduction of the SCR 48. It will be apparent that the resistor 54 could as well be a variable resistor to provide a convenient means of adjustment of the triggering level of the SCR 48.

It will be appreciated by those skilled in the art that the photoelectric device 52 may have sufficient capacity to directly energize the electromagnetic valve without the necessity of intermediate power amplification. An alternating voltage arrangement may be employed or a series diode may be utilized for direct current operation of the valve 22. In such an arrangement however, the on-off characteristic supplied by the SCR 48 circuit will not be available.

The light beam connection between the neon lamp 40 and the photoelectric device 52 provides an electrical isolation between the spark gap circuitry and the circuitry for energizing the electromagnetic valve 22, both of which may be operating a substantially different levels of potential. Although the neon lamp 40 and photoelectric device 52 are shown as separate units, it will be understood that recently available devices which incorporate these two units into a single assembly may be utilized as well since there is still isolation between the two circuits. In a similar manner, it will be apparent that different means might be utilized for monitoring the spark energy and transmitting this information to the electromagnetic valve circuitry for controlling the energization of the electromagnetic valve 22. Thus, as one example, an incandescent lamp could be substituted for the neon lamp 40 if sufficient energy were provided in the spark igniter circuit. Alternatively, the neon lamp 40 may be utilized only as a visual indicator to register proper operation of the spark ignition.

In normal operation of the elecu'omagnetic valve circuit when the SCR 48 is triggered into conduction, current flow will occur through the series circuit consisting of the fuse 44, the electromagnetic valve 22 and the SCR 48 on positive half cycles of the applied input voltage, the current being of an average value sufficient to energize the electromagnetic valve 22 at its nominal current rating. Due to the relative sensitivity to breakdown of the semiconductor material of the SCR 48 due to line transients and the like which might be caused, for example, by nearby lightening strokes, this circuitry also provides means for detecting such faults in the circuitry to prevent against energization of the electromagnetic valve 22 and a tum-on of the gas flow. In the normal operating condition the fuse 44, which may also be a circuit breaker or interrupter, is selected to have a current rating slightly greater than the average current flow through the electromagnetic valve 22. If the SCR 48 should break down due to line transients or internal defects and become a short circuit, both the positive and negative half-cycles of the input voltage will be applied across the electromagnetic valve 22. This will result in a current flow through the valve 22 of twice the value of the normal operating circuit. Since a typical electromagnetic valve in this environment would require approximately 75 ma., increased current flow due to the short circuit would result in a flow of approximately ma. Such differential in current levels is not readily recognized or definable by a fuse or circuit breaker since these devices do not ordinarily have a close tolerance. They are usually selected to carry current somewhat greater than the normal current flow so as not to cause burnouts within the normal range of line transients, due to the switching of currents within the circuit itself or to normal input voltage transients due to other devices connected to the external line circuitry. Therefore, the diode 50 across the electromagnetic valve 22 is provided to detect this reverse current flow through the electromagnetic valve 22, the diode 50 in this condition being forward biased to allow a substantially greater amount of current flow in the circuit and sufficiently great to overrate the fuse 44 and cause its burnout.

Connected across the spark gap 24 is a bimetal conductive leaf 60 which acts as a movable contact to electrically shunt the spark gap 24. The bimetal leaf 60 is located in close association with the burner 12 such that the heat emanating from the burner 12 when it has ignited acts upon the leaf 60 to cause a differential bonding thereof and a closure of the leaf 60 across the spark gap 24. Such shorting of the spark gap 24 after the burner 12 has been ignited for a short interval of time serves to extinguish the spark and prevent the emission of radio frequency interference. The shorting of the gap 24 will not substantially affect the spark energy emanating from the spark igniter 30 and thus does not substantially affect the monitoring circuit consisting of the resistor 38, capacitor 36 and neon lamp 40, and the neon lamp will remain in a lit condition. The output of the monitoring circuit then will maintain the electromagnetic valve 22 circuit in an energized condition maintaining the flow of gas to the burner 12. The shutting off of the gas to the burner 12 by means of the manual valve 14 will cause a cessation of heating of the bimetal strip 60 and a consequent opening of the gap 24 thereby preparing the circuit for relighting of the burner 12 when so desired. The time response of the bimetal strip 60 is ordinarily in the range of only several seconds which allows insufficient time for a great quantity of unburned gas to flow from the burner 12 before the ignition system becomes effective again.

It will be apparent to those skilled in the art that the apparatus of this invention has provided an improved spark ignition system that not only detects the presence of proper sparking at the gap but also recognizes failures within the system itself to prevent an accumulation of gases, and in addition, prosiderable improvement over prior art systems and provides a fail-safe operation in an environment which requires dependable control.

The second embodiment of rectifier safety circuit applicable for control of the electromagnetic valve 22 or any other load component is shown in FIG. 3. Here a load 62 is indicated, adapted for energization from a source of AC power applied at terminals 64, 65, being connected directly to terminal 65 by line 66 and connected to terminal 64 by way of the anode to cathode path of a silicon controlled rectifier (SCR) 68 and normally open contacts 69 of a DC relay 70. While an SCR 68 is depicted for controlled energization of the load 62 by gating signals applied at the gate electrode 71 thereof, it will be appreciated that the teachings of this invention are applicable as well ifa power rectifier is utilized in place of the SCR 68 for continuous energization of the load 62 on alternate half-cycles of the power source in a manner well understood in the art. The power rectifier, or SCR 68 when gated on, serves to provide unidirectional current flow through the load 62 when the contacts 69 are closed due to energization of the relay 70. v The means operatively connecting the SCR 68 and the load 62 include not only the contacts 69 but also the series connected components of the coil 72 of relay 70, a fixed resistor 74 and an element 75 for controlling current flow to the relay coil 72, the element 75 preferably being a fusible resistor. The safety circuit is completed with the connection of a rectifier 76 in series with the element 75, creating a circuit path for reverse current flow, that is, opposite to the unidirectional current flow normally obtained from the SCR 68, from terminal 65 through rectifier 76, element 75 and SCR 68 back to terminal 64, when the SCR is in a shorted condition.

Thus in normal operation, where SCR 68 is gated on, unidirectional current flow will occur through element 75, coil 72 and resistor 74, closing contacts 69 and causing current flow through the load 62. The effective resistance of element 75 may be as small as desired, and the element 75 could be a conventional wire-element or powdered fuse, having negligible resistance, however in the preferred embodiment of the invention some resistance is desired for limiting the level of current under fault conditions of SCR 68. The energization level of current through coil 72 may be further controlled by selection of an appropriate value for resistor 74.

Upon short circuit failure of SCR 68 full power will be applied to load 62, the additional current flow occum'ng on alternate half-cycles of the power source being such reverse current flow. Rectifier 76, which may be a conventional semiconductor diode, provides a path for the reverse current flow, in

shunt of the load 62 for protection thereof, through element 75. In the usual situafion such reverse current flow will be on the order of several times the level of unidirectional current flow and is limited essenfially by the resistance of element 75.

When overloading and thus burnout of element 75 occurs, relay coil 72 will be disconnected from the power source as will the load 62 through the action of the normally open contacts 69 of relay 70.

It will be apparent that the same circuit operation will obtain if the polarities of SCR 68 and rectifier 76 are reversed, the only requirement being that such elements be reversely poled with respect to one another so that the. rectifier 76 cooperates with the SCR 68 to create a current path, only when the latter is in a short circuit fault condition, when circuit protection is desired. Element 75 may also be a conventional carbon or wire wound resistor, selected with a wattage rating sufficient to accommodate unidirectional current flow and energization of coil 72, but greatly overloaded by the reverse current flow so as to burn out and cause disconnection of the circuit after a short interval of time. Such device provides the means for fault protection and current limiting in a readily replaceable and inexpensive component and it will be apparent that element 75 may be connected at other locations within this circuit to provide the same or similar functions.

We, therefore, particularly point out and distinctly claim as our invention:

1. Apparatus for protection of a load energized from an AC source of power, comprising a power rectifier for converting the AC power to unidirectional current for energization of the load, a relay having contacts in series connection with said power rectifier and the load, a fusible resistor for energizing the coil of said relay for closure of said contacts with unidirectional current flow, a second rectifier connected to direct reverse current flow due to short circuit failure of said power rectifier through said fusible resistor for deenergizing said relay coil, said power rectifier being in series connection with said fusible resistor and said second rectifier, the coil of said relay being operatively connected in parallel with said second rectifier, said fusible resistor being adapted for limiting unidirectional current flow through said relay coil and being adapted for burnout upon receipt of reverse current flow from said second rectifier.

2. Apparatus as set forth in claim 1 wherein said relay is a light current DC relay and further including a resistor in series connection with said relay coil for further limiting unidirectional current flow therethrough.

3. Apparatus as set forth in claim 2 wherein said power rectifier is a silicon controlled rectifier having a gate electrode for receiptof signals for energizing the load.

Claims (3)

1. Apparatus for protection of a load energized from an AC source of power, comprising a power rectifier for converting the AC power to unidirectional current for energization of the load, a relay having contacts in series connection with said power rectifier and the load, a fusible resistor for energizing the coil of said relay for closure of said contacts with unidirectional current flow, a second rectifier connected to direct reverse current flow due to short circuit failure of said power rectifier through said fusible resistor for deenergizing said relay coil, said power rectifier being in series connection with said fusible resistor and said second rectifier, the coil of said relay being operatively connected in parallel with said second rectifier, said fusible resistor being adapted for limiting unidirectional current flow through said relay coil and being adapted for burnout upon receipt of reverse current flow from said second rectifier.

2. Apparatus as set forth in claim 1 wherein said relay is a light current DC relay and further including a resistor in series connection with said relay coil for further limiting unidirectional current flow therethrough.

3. Apparatus as set forth in claim 2 wherein Said power rectifier is a silicon controlled rectifier having a gate electrode for receipt of signals for energizing the load.

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