GB1559904A - Spark ignition - Google Patents

Description

(54) IMPROVEMENTS RELATING TO SPARK IGNITION UNITS (71) We, THE PLESSEY COMPANY LIMITED, a British Company, of Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- This invention relates to spark ignition units for gas cookers and other gas appliances and relates more specifically to such units for providing a plurality of ignition sparks simultaneously at spark gaps associated with burners of the appliance.

In the case of one specific form of spark ignition unit for use in multi-burner gas cooker the unit comprises a capacitor charge/discharge arrangement for producing a high voltage pulse output from each of a plurality of secondary windings of a high voltage transformer. The unit is provided with a high voltage output terminal for each of these secondary windings and these terminals are intended to be connected to spark gaps associated with respective burners of the cooker. In the interests of standardisation and cheapness of manufacture it is customary for these multi-outlet spark ignition units to be provided with a predetermined standard number of output terminals (e.g. six). Consequently, when these units are embodied in gas cookers having fewer than six burners one or more of the output terminals will be unused.If the or each unused output terminal is just left unconnected there is a marked tendency for the insulation of the secondary transformer winding associated with the unconnected terminal to break down electrically whereas if the unconnected terminals are connected to earth tracking tends to occur between the earth terminal and one or more adjacent high voltage output terminals.

According to the present invention there is provided a spark ignition unit for a gas appliance, said unit in use providing a plurality of sparks simultaneously at spark gaps associated with burners of the appliance, in which the unit comprises dummy spark gap means fitted to a high tension terminal of the unit not required to be connected to a spark gap of the appliance.

The dummy spark gap means may simply comprise an air gap included in a high tension cable connected to earth or it may comprise an earthed metallic tape secured by adhesive to a housing for the unit and located within spark over distance from the unconnected high tension terminal.

By way of example the present invention will now be described with reference to the single-figure drawing accompanying the Provisional Specification which shows a plan view of a multi-outlet spark ignition unit fitted with a dummy spark gap device.

Referring to the drawing the multi-outlet spark ignition unit comprises an input transformer T1 the primary winding of which will be connected across and a.c. mains supply. The output from the secondary winding of the transformer T1 is rectified by diode Dl and charges a capacitor C1.

Connected across this capacitor C1 are a plurality of parallel paths each of which comprises a resistor Rp and capacitor Cp and which in use of the unit includes a switch associated with a burner of a gas cooker. A further parallel branch includes a diode D2 and a thyristor TH1 is arranged to be rendered conducting by a triggering pulse delivered to the trigger electrode of the thyristor from one or more trigger circuits including neon tubes N1 to N6 connected, respectively, to the aforesaid capacitor resistor paths, whenever one or more switches associated with the burners are operated.

When the thyristor TH1 is rendered conductive the charged capacitor Cl discharges through the primary winding of a high voltage output transformer T2 having six secondary windings Si to S6. The secondary windings are connected on one side to output terminals TL1 to TL6. These terminals will be connected as by high tension cables to spark electrodes of spark gaps associated with the cooker burners.

In the event that the gas cooker does not have six burners then a dummy spark gap device DSD may be connected at one end to the unused terminal of the output terminals whilst the other end of the dummy spark gap device is connected to earth. The dummy spark gap device DSD may take various forms. For example, the device may simply comprise a cable having a spark gap embodied in the conductive path thereof.

By use of the dummy spark gap means according to the invention the problems of tracking between a directly earthed terminal and an adjacent high tension terminal or the problem of electrical breakdown of the secondary winding associated with an unconnected terminal is avoided.

WHAT WE CLAIM IS:- 1. A spark ignition unit for a gas appliance, said unit in use providing a plurality of ignition sparks simultaneously at spark gaps associated with burners of the appliance, in which the unit comprises dummy spark gap means fitted to a high tension terminal of the unit not required to be connected to a spark gap of the appliance.

2. A spark gap ignition as claimed in claim 1, in which the dummy spark gap means comprises an air gap included in a high tension cable connected to earth.

3. A spark ignition unit as claimed in claim 1, in which the dummy spark gap means comprises an earthed metallic tape secured as by adhesive, to a housing of the unit and located within spark over distance from the unconnected high tension terminal.

4. A spark ignition unit substantially as hereinbefore described with reference to the drawing accompanying the Provisional Spe cification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. to spark electrodes of spark gaps associated with the cooker burners. In the event that the gas cooker does not have six burners then a dummy spark gap device DSD may be connected at one end to the unused terminal of the output terminals whilst the other end of the dummy spark gap device is connected to earth. The dummy spark gap device DSD may take various forms. For example, the device may simply comprise a cable having a spark gap embodied in the conductive path thereof. By use of the dummy spark gap means according to the invention the problems of tracking between a directly earthed terminal and an adjacent high tension terminal or the problem of electrical breakdown of the secondary winding associated with an unconnected terminal is avoided. WHAT WE CLAIM IS:-

1. A spark ignition unit for a gas appliance, said unit in use providing a plurality of ignition sparks simultaneously at spark gaps associated with burners of the appliance, in which the unit comprises dummy spark gap means fitted to a high tension terminal of the unit not required to be connected to a spark gap of the appliance.

2. A spark gap ignition as claimed in claim 1, in which the dummy spark gap means comprises an air gap included in a high tension cable connected to earth.

3. A spark ignition unit as claimed in claim 1, in which the dummy spark gap means comprises an earthed metallic tape secured as by adhesive, to a housing of the unit and located within spark over distance from the unconnected high tension terminal.

4. A spark ignition unit substantially as hereinbefore described with reference to the drawing accompanying the Provisional Spe cification.