Merrychef 501 Service Manual download pdf (Page 10)

Page 10 Mealstream Ovens 32Z3387 Issue 2

Procedure A - Power Output Test in accordance with

BS EN 60335-2-90 Annex AA

This test is given in the BSI test standard for microwave ovens. It is reproduced below - not so that

you can follow it, but to show you why it is impractical in normal conditions. A simplified procedure,

which gives a good approximation to the BSI power output, is given in Procedure B which follows.

Note: This test can only be carried out on a COLD oven. If the oven has been operating, even for

only a few seconds, the power given will be lower than the oven rating. This test must also be carried

out at a stable voltage - the voltage in most kitchens varies considerably even within the period of the

test. If the oven has been operating, go to Procedure B.

You will need:

A thermometer capable of reading to ±0.1°C.

A cylindrical borosilicate glass container, 190 mm diameter, with a wall thickness of

3 mm or less.

A calculator.

A set of scales capable of reading 1kg to an accuracy of ± 1g.

A glass or plastic stirrer.

A jug capable of holding over 1 litre of water.

Drinkable water which is at a temperature of 10°C ± 1°C.

A “Variac” or similar variable transformer capable of supplying the oven to ensure a

stable voltage.

WARNING: The Borosilicate Glass container has thin walls and is therefore fragile

- take care not to break it during use.

Method

A cylindrical container of borosilicate glass is used for the test. It has a maximum thickness of

3mm, an external diameter of approximately 190mm and a height of approximately 90mm. The

mass of the container is determined.

At the start of the test, the oven and the empty container are at ambient temperature. Potable water

having an initial temperature of 10°C ± 1°C is used for the test. The temperature of the water is

measured immediately before it is poured into the container.

A quantity of 1000g ± 5g of water is added to the container and its actual mass obtained. The

container is then immediately placed in the middle of the oven base. The appliance is supplied at

rated voltage and operated at the maximum power setting. The time for the water temperature to

attain 20°C ± 2°C is measured. The oven is then switched off and the final water temperature is

measured within 60seconds.

NOTES:

1 The water is stirred before its temperature is measured.

2 Stirring and measuring devices are to have a low heat capacity.

The microwave power output is calculated from the formula:

4.187 M

-T

) + 0.55 M

-T

)

P =

where

P is the microwave power output, in watts;

is the mass of the water, in grams;

is the mass of the container, in grams;

is the ambient temperature, in °C;

is the initial temperature of the water, in °C;

is the final temperature of the water, in °C;

t is the heating time in seconds, excluding the magnetron filament heat-up time.

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