Microwave Glass
Testing Microwave Ovens
Microwaves ovens use high frequency electromagnetic waves to cook the food. In a properly designed and constructed oven, these high energy waves are contained entirely within the cooking area. However if these waves were to leak out they can result in serious burns to the user. Levels of radiation above 5mW/sq.cm are considered harmful to humans.
What can cause Microwaves to leak
Microwaves are designed to keep all the energy within the cooking area with negligible leakage. However damage to the microwave such as broken door hinges, door catches, damaged or missing door seals or cracks or damage to the glass door can result in excessive leakage.
Microwave leakage checkerscan be used for checking the level of leakage from microwave ovens. It is very important to ensure that the leakage checkers have been properly calibrated before they are used.
Most leakage checkers have a display to show the level of leakage. They also have a spacer built in to make sure it is the correct distance from the body of the microwave when the measurement is being taken. When taking measurements, it is important to try it in different orientations to check for maximum leakage.
Verifying that the leakage checker is working
It is good practice to do a quick check to see that the microwave leakage checker is working before a measurement is taken. This can easily be done by using a mobile phone. Just hold this against the leakage checker and make a call. The display should show a reading to indicate that it is working.
This is only a quick field check and not a replacement for annual calibration. The unit must be sent back annually to the manufacturers or a reputable calibration house for this.
Checking for leakage
To check a microwave oven for leakage it needs to be working. A standard test will take about a minute. The easiest way to do this is to put a large bowl of water in the microwave oven and start it cooking at full power for 1 minute.
Use the microwave leakage checker to scan the front glass and the door seals to check for leakage. Remember to use the checker in different orientations while looking for the highest leakage. If the result goes into the red at any time, the oven will have to be failed. If it is always in the green then everything is safe. If it is always in the orange then while this is not a fail it is a cause for concern and one should consider replacing the microwave at the earliest opportunity.
Remember to check that the safety interlock works. This is verification that when the microwave is working and the door is opened the waves are switched off.
Reasons for testing microwave heating power
Anyone selling a used microwave oven is strongly recommended to check the heating power of microwave ovens. Many cooking recipes specify cooking times based on microwave power. If this is not being achieved in use then there is a risk of under-cooking food with the resulting risk of food poisoning.
Microwave can lose power for many reasons. The microwave source could deteriorate with time, the connections to the source could become corroded or there could be a build up of food on critical parts.
Carrying out a heating power test
We will need a plastic measuring jug and a thermometer for this. Fill the jug with about 300 ml of water and note the temperature. Heat this in the microwave oven at full power for a whole minute. Stir the water and note the final temperature.
The volume of water, the temperature rise and the heating time is used in this equation to work out the heating power of the microwave. If this is significantly different from the manufacturer’s specification, then the microwave should not be sold.
Equation: Microwave power (watts) = 4.2 x (Volume of water in ml) X temperature rise / time (in seconds)
In summary all microwaves have to be tested for leakage with a suitably calibrated checker. A check of the safety interlock is also necessary. Used microwaves need to pass a heating power test before they are made available for sale.
About the Author
Seggy Segaran is an industry expert in Portable Appliance Testing. He has two books on PAT Testing published and available for sale on Amazon.
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