GB1573679A - Arrangements including electrical heating elements - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ARRANGEMENTS INCLUDING ELECTRICAL IlEATING ELEMENTS (71) We, ENGLISH ELECTRIC VALVE COMPANY LIMITED, a British Company, of 106, Waterhouse Lane, Chelmsford, Essex. CM1 2QU. 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 statement: This invention relates to electronic valve arrangements and in particular to such arrangements including an electronic valve having within the envelope thereof an electrical heating element the temperature of which it is required to stabilise. Whilst applicable to many forms of such arrangements, e.g. those in which the electrical heating element is a cathode heater, the invention is particularly applicable to certain thyratron arrangements.

Usually a thyratron has a gas filling of hydrogen or an hydrogen isotope such as deuterium or tritium.

The pressure of such a gas filling critically affects the performance of the thyratron and it is common practice to include in a reservoir a gas pressure determining capsule, usually of titanium hydride, the temperature of which determines the pressure of the gas filling. In the case of titanium hydride the effect is achieved due to dissociation of the hydride which is a function of its temperature and in order to maintain this temperature as steady as possible the capsule is usually arranged to be heated electrically by an electric heating element.

The present invention seeks to provide an improved electronic valve arrangement including an electronic valve having within the envelope thereof an electrical heating element and in particular a gas filled thyratron arrangement in which the thyratron valve has a pressure determining capsule therein which is electrically heated by an electrical heating element, wherein means are provided tending to stabilise the temperature of the heating element.

According to this invention an electronic valve arrangement including an electronic valve having within the envelope thereof a heating element of temperature dependent resistance is provided said arrangement including a controllable attenuator, means for applying electrical energy to said heating element via a path including said controllable attenuator, means for deriving a signal corresponding to voltage appearing across said heating element, means for deriving a signal corresponding to the current flowing through said heating element and means for comparing said two derived signals to provide a control signal for said controllable attenuator whereby as the resistance of said heating element changes as a result of its temperature changing so the attenuator is controlled to affect a compensating adjustment in the level of electrical energy applied to said heating element.

Preferably said electronic valve is a thyratron and said electrical heating element is the electrical heating element of a reservoir in said thyratron containing a gas pressure determining capsule.

Preferably said controllable attenuator comprises a resistor in the path of said electrical energy supplied to said heating element, which resistor is shunted by switch means arranged to be conductive or non conductive under the control of said comparison means.

Said switch means may be mechanical in nature, but preferably said switch means is electronic and preferably constituted by a triac device.

Preferably said heating element is connected to be supplied with electric energy via a transformer, the primary winding of which is connected across two a.c. power supply input terminals via two resistors, one of which comprises the resistor forming part of said controllable attenuator and the other of which provides a voltage drop in operation, which is related to the value of current flowing through said heating element, means being provided for monitoring said last mentioned voltage drop in order to provide said signal corresponding to the value of current flowing through said heating element.

Preferably said means for deriving a signal corresponding to the voltage across said heating element comprises a capacitor connected to be charged via a rectifier by the voltage appearing across the primary winding of said transformer.

Preferably a tapped resistor is connected across said capacitor, the tap of said tapped resistor being arranged to provide one input to said comparison means.

Preferably said means for monitoring the voltage across said current measuring resistor comprises a further capacitor connected to be charged via a further rectifier to a voltage dependent upon the voltage appearing across said current measuring resistor.

Preferably a further tapped resistor is connected across said last mentioned capacitor, the tap of said last mentioned resistor being connected to a second input of said comparison means.

Normally the value of said resistor comprising part of said controllable attenuator is chosen such that when this is in circuit by virtue of the state of said switch means the temperature of said heating element is lower than a predetermined desired value and when said last mentioned resistor is short circuited, by virtue of the action of said switch means the temperature of said heating element is above said predetermined value.

The invention is illustrated in and further described with reference to the accompanying drawing which is a circuit diagram of one arrangement in accordance with the present invention for stabilising the heating element of a thyratron.

Referring to the drawing, 1 represents the reservoir heating element within the envelope of a thyratron (not shown) which has a titanium hydride gas pressure determining capsule within a reservoir which is heated by the heating element 1. An a.c. source (not shown) of heating current for the heating element 1 is provided to be connected across a.c. input terminals 2, which are connected via resistors 3 and 4 across the primary winding 5 of a transformer 6, the secondary winding 7 of which is connected across the heating element 1.

A capacitor 8 is connected to be charged by the voltage appearing across the primary winding 5 of transformer 6 after rectification by a rectifier 9. A tapped resistor 10 is connected across capacitor 8 with its movable tap 11 connected to one input of a comparator 12.

The other input of comparator 12 is connected to the movable tap 13 of a further tapped resistor 14 which is connected across a further capacitor 15, which in turn is arranged to be charged from voltage appearing across resistor 4 after rectification by a rectifier 16.

Connected across resistor 3 is an electronic switch, in this case a triac 17, which is controlled as to its state of conduction by the output of comparator 12.

In operation, the tap 11 of tapped resistor 10 is adjusted together with tap 13 of tapped resistor 14 in order to provide suitable levels of voltages for comparison by the comparator 12 and in order to provide similar time constants for the charging circuits of capacitors 8 and 15. Capacitor 8 will charge to the peak voltage of the waveform appearing across the primary 5 of transformer 6, whilst capacitor 15 will charge to the peak voltage appearing across resistor 4. The ratio of the peak voltages will depend upon the resistance of reservoir heating element 1 which, being of tungsten, has a temperature/resistance characteristic which is such that its resistance increases as its temperature increases.

The value of resistor 3 is chosen such that when this is in circuit the temperature of heating element 1 would be lower than that required, whilst when resistor 3 is short circuited by triac 17 the temperature of heating element 1 would be higher than that required.

When the heating element 1 is below its predetermined operating temperature, the comparator 12 triggers triac 17 into conduction causing the temperature of heating element 1 to rise. As this temperature passes the predetermined value the comparator 12 stops triggering triac 17, allowing the heating element 1 to cool below the predetermined value. The cycle is then repeated. This tends to maintain the temperature of the heating element 1 at a level corresponding to the balance point of the comparator circuit. The balance point itself may be adjusted either by adjusting the taps 11 and 13 of tapped resistors 10 and 14 or by adjusting the value of resistor 4.

WHAT WE CLAIM IS: 1. An electronic valve arrangement including an electronic valve having within the envelope thereof a heating element of temperature dependent resistance, said arrangement including a controllable attenuator, means for applying electrical energy to said heating element via a path including said controllable attenuator, means for deriving a signal corresponding to voltage appearing across said heating element, means for deriving a signal corresponding to

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

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. of said controllable attenuator and the other of which provides a voltage drop in operation, which is related to the value of current flowing through said heating element, means being provided for monitoring said last mentioned voltage drop in order to provide said signal corresponding to the value of current flowing through said heating element. Preferably said means for deriving a signal corresponding to the voltage across said heating element comprises a capacitor connected to be charged via a rectifier by the voltage appearing across the primary winding of said transformer. Preferably a tapped resistor is connected across said capacitor, the tap of said tapped resistor being arranged to provide one input to said comparison means. Preferably said means for monitoring the voltage across said current measuring resistor comprises a further capacitor connected to be charged via a further rectifier to a voltage dependent upon the voltage appearing across said current measuring resistor. Preferably a further tapped resistor is connected across said last mentioned capacitor, the tap of said last mentioned resistor being connected to a second input of said comparison means. Normally the value of said resistor comprising part of said controllable attenuator is chosen such that when this is in circuit by virtue of the state of said switch means the temperature of said heating element is lower than a predetermined desired value and when said last mentioned resistor is short circuited, by virtue of the action of said switch means the temperature of said heating element is above said predetermined value. The invention is illustrated in and further described with reference to the accompanying drawing which is a circuit diagram of one arrangement in accordance with the present invention for stabilising the heating element of a thyratron. Referring to the drawing, 1 represents the reservoir heating element within the envelope of a thyratron (not shown) which has a titanium hydride gas pressure determining capsule within a reservoir which is heated by the heating element 1. An a.c. source (not shown) of heating current for the heating element 1 is provided to be connected across a.c. input terminals 2, which are connected via resistors 3 and 4 across the primary winding 5 of a transformer 6, the secondary winding 7 of which is connected across the heating element 1. A capacitor 8 is connected to be charged by the voltage appearing across the primary winding 5 of transformer 6 after rectification by a rectifier 9. A tapped resistor 10 is connected across capacitor 8 with its movable tap 11 connected to one input of a comparator 12. The other input of comparator 12 is connected to the movable tap 13 of a further tapped resistor 14 which is connected across a further capacitor 15, which in turn is arranged to be charged from voltage appearing across resistor 4 after rectification by a rectifier 16. Connected across resistor 3 is an electronic switch, in this case a triac 17, which is controlled as to its state of conduction by the output of comparator 12. In operation, the tap 11 of tapped resistor 10 is adjusted together with tap 13 of tapped resistor 14 in order to provide suitable levels of voltages for comparison by the comparator 12 and in order to provide similar time constants for the charging circuits of capacitors 8 and 15. Capacitor 8 will charge to the peak voltage of the waveform appearing across the primary 5 of transformer 6, whilst capacitor 15 will charge to the peak voltage appearing across resistor 4. The ratio of the peak voltages will depend upon the resistance of reservoir heating element 1 which, being of tungsten, has a temperature/resistance characteristic which is such that its resistance increases as its temperature increases. The value of resistor 3 is chosen such that when this is in circuit the temperature of heating element 1 would be lower than that required, whilst when resistor 3 is short circuited by triac 17 the temperature of heating element 1 would be higher than that required. When the heating element 1 is below its predetermined operating temperature, the comparator 12 triggers triac 17 into conduction causing the temperature of heating element 1 to rise. As this temperature passes the predetermined value the comparator 12 stops triggering triac 17, allowing the heating element 1 to cool below the predetermined value. The cycle is then repeated. This tends to maintain the temperature of the heating element 1 at a level corresponding to the balance point of the comparator circuit. The balance point itself may be adjusted either by adjusting the taps 11 and 13 of tapped resistors 10 and 14 or by adjusting the value of resistor 4. WHAT WE CLAIM IS:

1. An electronic valve arrangement including an electronic valve having within the envelope thereof a heating element of temperature dependent resistance, said arrangement including a controllable attenuator, means for applying electrical energy to said heating element via a path including said controllable attenuator, means for deriving a signal corresponding to voltage appearing across said heating element, means for deriving a signal corresponding to

the current flowing through said heating element and means for comparing said two derived signals to provide a control signal signal for said controllable attenuator whereby as the resistance of said heating element changes as a result of its temperature changing so the attenuator is controlled to affect a compensating adjustment in the level of electrical energy applied to said heating element.

2. An arrangement as claimed in claim 1 and wherein said electronic valve is a thyratron and said electrical heating element is the electrical heating element of a reservoir in said thyratron containing a gas pressure determining capsule.

3. An arrangement as claimed in claim 1 or 2 and wherein said controllable attenuator comprises a resistor in the path of said electrical energy supplied to said heating element, which resistor is shunted by switch means arranged to be conductive or non conductive under the control of said comparison means.

4. An arrangement as claimed in claim 3 and wherein said switch means is mechanical in nature.

5. An arrangement as claimed in claim 3 and wherein said switch means is electronic.

6. An arrangement as claimed in claim 5 and wherein said switch means is constituted by a triac device.

7. An arrangement as claimed in any of the above claims and wherein said heating element is connected to be supplied with electric energy via a transformer, the primary winding of which is connected across two a.c. power supply input terminals via two resistors, one of which comprises the resistor forming part of said controllable attenuator and the other of which provides a voltage drop, in operation, which is related to the value of current flowing through said heating element, means being provided for monitoring said last mentioned voltage drop in order to provide said signal corresponding to the value of current flowing through said heating element.

8. An arrangement as claimed in claim 7 and wherein said means for deriving a signal corresponding to the voltage across said heating element comprises a capacitor connected to be charged via a rectifier by the voltage appearing across the primary winding of said transformer.

9. An arrangement as claimed in claim 8 and wherein a tapped resistor is connected across said capacitor, the tap of said tapped resistor being arranged to provide one input to said comparison means.

10. An arrangement as claimed in any of claims 7 to 9 and wherein said means for monitoring the voltage across said current measuring resistor comprises a further capacitor connected to be charged via a further rectifier to a voltage dependent upon the voltage appearing across said current measuring resistor.

11. An arrangement as claimed in claim 10 and wherein a further tapped resistor is connected across aid last mentioned capacitor, the tap of said last mentioned resistor being connected to a second input of said companson means.

12. An arrangement as claimed in any of claims 7 to 11 and wherein the value of said resistor comprising part of said controllable attenuator is chosen such that when this is in circuit by virtue of the state of said switch means the temperature of said heating element is lower than a predetermined desired value and when said last mentioned resistor is short circuited, by virtue of the action of said switch means the temperature of said heating element is above said predetermined value.

13. An arrangement for providing a stabilising effect on the temperature of an electrical heating element having a temperature dependent resistance substantially as herein described with reference to the accompanying drawing.