GB2321764A

GB2321764A - Device for measuring the temperature of a magnetron for a microwave oven

Info

Publication number: GB2321764A
Application number: GB9801710A
Authority: GB
Inventors: Jean-Claude Derobert; Charles Denis
Original assignee: Moulinex SA
Current assignee: Moulinex SA
Priority date: 1997-01-31
Filing date: 1998-01-27
Publication date: 1998-08-05
Anticipated expiration: 2018-01-27
Also published as: CN1200460A; GB2321764B; CN1135595C; FR2759238A1; GB9801710D0; KR19980070965A; FR2759238B1; JPH10260081A

Abstract

A temperature sensor is fixed to a support (2) made of heat-conducting material, intended to be removably mounted on a cooling fin (15') of a magnetron (1) of a microwave oven so as to measure a temperature representative of the temperature of the anode block (11). If the temperature rises too high, indicative of abnormal conditions such as no load or cooling malfunction, power to the magnetron is cut off.

Description

DEVICE FOR MEASURING TEE TENPERATURE OF A MAGNETRON FOR A MICROWAVE OVEN The present invention concerns a device for measuring the temperature of a microwave oven magnetron by means of a temperature sensor, the said magnetron being of the type having a casing enclosing an anode block, and fins for cooling the magnetron extending transversely with respect to the said anode block.

In a microwave oven having a cavity forming a cooking chamber, fed with energy by a magnetron, it is known that the load variations within the cavity give rise to a variation in the amount of standing-waves, which results in a variation in temperature of the anode block of the magnetron.

By using the information consisting in the temperature of the anode block, it is therefore possible to recognise abnormal conditions of use of the oven, such as for example operating empty or with only the oven accessories (trays, turntable etc), or a malfunction in the cooling system (blockage of the magnetron cooling fan, obstruction of the oven ventilation holes, etc).

In the measuring devices currently used, the temperature is taken by means of a thermostat fixed at the external surface of the magnetron casing. The thermostat is also connected to the magnetron power supply circuit so as to be able if necessary to cut off this power supply when abnormal operation is detected.

The major drawback of this type of device lies in its response time, which is often too high, so that it does not effectively fulfil its role of protecting the magnetron.

This high response time is due on the one hand to the distant position of the thermostat with respect to the anode block and on the other hand to the fact that it is necessary to ventilate the magnetron strongly, which falsifies the measurement.

The aim of the present invention is to propose a novel temperature measurement device whose response time is improved.

This aim is achieved according to the invention by the fact that the temperature sensor is fixed to a support made of heatconducting material, intended to be mounted on at least one cooling fin so as to measure a temperature representative of the temperature of the anode block.

In this way, the temperature sensor is not only as close as possible to the anode block but is also less influenced by the ventilation of the magnetron.

Other characteristics of the invention will emerge during the description given below with reference to the accompanying drawings, in which: - Figure 1 illustrates in perspective a magnetron equipped with a support for a temperature measurement device according to a first embodiment of the invention; - Figure 2 is a plan view of the support of Figure 1; - Figure 3 is a side view of the support of Figure 2; - Figure 4 is a plan view of a measurement device support according to a second possible embodiment in accordance with the invention; - Figure 5 is a side view of the support of Figure 4.

The magnetron 1 depicted schematically in Figure 1 has in a conventional fashion a casing 10 enclosing an anode block 11, with a generally cylindrical envelope. The anode block surrounds a cathode which is not visible in the figure. When the magnetron is powered, the anode block 11 receives electrons emitted by the cathode. The electron field is concentrated by means of a pair of generally cylindrical magnets 12, 13, placed concentrically at each end of the anode block 11. The microwaves are emitted by an antenna 14. A plurality of fins 15 extend transversely with respect to the anode block 11 in order to cool this block in operation.

Instead of taking a measurement of the temperature at the casing 10, the present invention provides for a measuring device in which the temperature sensor, not shown in order not to overload the figures, is fixed to a support 2 made of heat-conducting material which is mounted on at least one cooling fin 15'.

Advantageously, the support 2 is removably mounted on the cooling fin 15'.

In the two embodiments given by way of example in the figures, the support 2 is substantially plane in shape. It comprises a base 20, having for example an opening 21 for receiving the temperature sensor. The support 2 is held on the cooling fin 15' for example by means of two lugs 22 connected to the base 20 of the support, and forming with this base 20 two elastic clamps gripping the cooling fin 15'.

In addition, two arms 23; 24 extend in the same direction from the base 20 and are positioned on each side of the anode block 11 when the support is mounted on the cooling fin 15', as illustrated in Figure 1. In order to ensure that the support 2 remains firmly in place on the cooling fin, provision can be made to fold the free ends of the two arms 23 at right angles on the rear of the fin, as depicted in broken lines in Figure 1.

In the example embodiment illustrated in Figures 1 to 3, the two arms 23 extend parallel to the plane of the fin 15' and are in contact with the said fin. In addition, the temperature sensor is mounted in the opening 21 so as preferably also to be in contact with the fin 15' The information relating to the temperature of the anode block 11 is therefore transmitted to the sensor via the cooling fin and the support arms 23.

In a particularly advantageous variant embodiment illustrated in Figures 4 and 5, the two arms 24 which extend from the base 20 are shaped so as to encircle the shape of the anode block 11 when the support is mounted on the cooling fin. The temperature sensor therefore receives, via the arms 24, a measurement which is even more representative of the temperature of the anode block, with an improved response time.

The material of the support must in these cases be a good conductor of heat. An austenitic stainless steel will preferably be chosen.

It will easily be understood that other embodiments can be envisaged without departing from the scope of the invention.

Thus the support can be of highly diverse shapes in order to receive several types of temperature sensor. Moreover, the sensor used can be a simple thermostat, or an electronic component with a positive temperature constant (PTC) or negative temperature constant (NTC).

Claims

CLAIMS:

1. Device for measuring the temperature of a microwave oven magnetron (1) by means of a temperature sensor, the said magnetron being of the type having a casing (10) enclosing an anode block (11), and fins (15, 15') for cooling the magnetron extending transversely with respect to the said anode block, characterised in that the temperature sensor is fixed to a support (2) made of heat-conducting material, intended to be mounted on at least one cooling fin (15') so as to measure a temperature representative of the temperature of the anode block.

2. Measuring device according to Claim 1, characterised in that the said support (2) is removably mounted on the cooling fin (15').

3. Measuring device according to either one of the preceding claims, characterised in that the said support (2) is substantially plane in shape, comprising a base (20) on which the temperature sensor is fixed, and two arms (23; 24) extending in the same direction from the base (20) so as to be positioned on each side of the anode block (11) when the support is in place on the cooling fin.

4. Measuring device according to Claim 3, characterised in that the support (2) is mounted on the cooling fin (15') by means of lugs (22) connected to the base (20), each lug forming with the base an elastic clamp gripping the cooling fin (15').

5. Measuring device according to either one of Claims 3 and 4, characterised in that the two arms (23) extend parallel to the plane of the cooling fin (15') and are in contact with the said fin.

6. Measuring device according to either one of Claims 3 and 4, characterised in that the two arms (24) are shaped so as to encircle the shape of the anode block (11) when the support is in place on the cooling fin (15')

7. Measuring device according to any one of the preceding claims, characterised in that the material of the support is made of austenitic stainless steel.

8. Measuring device according to any one of the preceding claims, characterised in that the temperature sensors consists of a thermostat.

9. Measuring device according to any one of the preceding claims, characterised in that the temperature sensor consists of an electronic component of the type with a positive temperature coefficient (PTC) or negative temperature coefficient (NTC).

10. Measuring device substantially as hereinbefore described with reference to the accompanying drawings.