GB2243277A - Microwave oven - Google Patents

Abstract

The magnetron 1 of a microwave oven is controlled by a microprocessor 4 which includes a non-volatile memory 10 in which the cumulative length of time for which the magnetron has been energised is recorded. This information may then be displayed on the control panel when suitable instructions have been keyed in, or the microprocessor may be so programmed as to compensate for such ageing of the magnetron by automatically increasing cooking times beyond those set. <IMAGE>

Description

Microwave Oven This invention relates to microwave ovens.

When cooking food in a microwave oven, it is important that the food reaches a temperature sufficient to destroy harmful bacteria. For a given magnetron power output, the temperature reached by the food is controlled by controlling the time for which the magnetron is energised.

However, it is a characteristic of magnetrons that power output declines slowly over their lifetime. Thus, food which may be sufficiently cooked within a certain time when the magnetron is new may be insufficiently cooked using the same cooking time when the magnetron is nearing the end of its life.

The invention provides a microwave oven including means to record the length of-time for which the magnetron is energised.

By measuring the total time for which the magnetron is energised, it is possible for a user to become aware of any risk of undercooking of food and/or for appropriate compensation to be made in the cooking time.

A microwave oven constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawing, which is a circuit diagram including the magnetron of the microwave oven.

The magnetron 1 of the microwave oven is powered from mains terminal 2 via a step-up transformer 3 which feeds the magnetron from secondary winding W with dc voltage of about 4 k.V. via a voltage doubler consisting of a capacitor C in series with a diode D. A separate secondary winding W1 is provided for heating the cathode of the magnetron.

The magnetron is switched on and off by means of relay R controlled by a microprocessor 4, into which cooking commands are input from a keyboard 5. Keyboard 5 has keys enabling the cooking time and power output level eg low, roast, high, to be set, and displayed on display 6.

The microprocessor includes ROM 7 containing software for controlling the operation of the magnetron, and RAM 8 into which data can be written and from which data can be read for storing data keyed into the keyboard 5.

Cooking can only be commenced by depression of an interlock switch 9 which cannot be depressed until the oven door is closed. Closure of the interlock switch 9 closes contacts in the live line as well as "sense" contacts ganged to those in the live line, which sense when the oven door has been closed and which permit the microprocessor 4 to energise relay R.

In accordance with the invention, a non-volatile memory 10 is also provided, and the microprocessor is programmed to count when the relay R is closed and to store that data additively in the memory 10, transferring the data either at preset intervals of time or when the relay is next opened. Thus, a running total is kept of the time for which the magnetron is energised. An EEPROM may be used for the non-volatile memory, and it may be part of RAM 8 but with a battery back-up.

In one embodiment of the invention, ROM 7 contains an algorithm which automatically increases the cooking time set by the user in accordance with the ageing characteristics of the type of magnetron used. This may be done by causing the automatic timer to run more slowly, or the timing rate may be kept constant and the cooking time duration set may be automatically increased. However, if desired, the display could simply indicate, when suitable instructions have been keyed in, the longer time required for cooking, enabling the user to set the appropriate increased time.

In an especially simple arrangement, in order for the user to be able to know how much the magnetron has been used, the cumulative time of energisation of the magnetron could be displayed when suitable instructions have been keyed in.

Claims (4)

1. A microwave oven including means to record the length of time for which the magnetron is energised.

2. A microwave oven as claimed in claim 1, in which a non-volatile memory is provided to record the information.

3. A microwave oven as claimed in claim 1 or claim 2, including means for increasing the cooking time in relation to that set by the user in dependence on stored data relating the length of time for which the magnetron has been energised and its corresponding power output.

4. A microwave oven substantially as herein described with reference to the accompanying drawings.

4. A microwave oven substantially as herein described with reference to the accompanying drawings.

AMENDMENTS TO THE CLAIMS H AVE BEEN FILED AS FOLLOWS.

1. A microwave oven including means to record the cumulative length of time for which the magnetron has been energised.

2. A microwave oven as claimed in claim 1, in which a non-volatile memory is provided to record the information.

3. A microwave oven as claimed in claim 1 or claim 2, including means for increasing the cooking time in relation to that set by the user in dependence on stored data relating the length of time for which the magnetron has been energised and its corresponding power output.