TEST PROCEDURES
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LETTER | COMPONENT | TEST |
MAGNETRON ASSEMBLY TEST
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPO- NENTS OR WIRING.
To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check across the magnetron filament leads should indicate less than 1 ohm.
To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads and chassis ground. This test should indicate an infinite resistance. If there is little or no
’resistance, the magnetron is grounded and must be replaced.
Power output of the magnetron can be measured by performing a water temperature rise test. This test should only be used if above rests do not indicate a faulty magnetron and there is no
defect in the following components or wiring: high voltage rectifier, rectifier, high voltage capacitor, and power transformer.
MICROWAVE OUTPUT POWER
Microwave output power from the magnetron can be measured by way of substitution, i.e. it can be measured by using water load how much it can be absorbed by the water load. To measure the microwave output power in the microwave oven, the relation of calorie and watt is used.
When P(W) heating works for t(second), approximately P x t/4.2 calorie is generated. On the other hand, if the temperature of the water with V(ml) rises AT ( “C) during this microwave heating period, the calorie of the water is V x AT.
The formular is as follows;
Pxt/4.2=Vx AT
P(W)=4.2xVx AT/t
Our condition for the water load is as follows:
Water load ... 2000 ml, Heating time ...I 20 seconds
P=7Ox AT
Measuring method;
1.Put the water load of two (2) litres on the center of the oven shelf. The water load should be arranged in two (2) Pyrex beakers, the size of which is one (1) litre, and be placed at right and left, side by side, on the oven shelf.
2.Measure the temperature of water before heating and also after heating during 120 seconds by microwave, and calculate the temperature rise. The temperature rise should be the average of temperature differences measured in each beaker.
3.The output power should be calculated as follows. In case the measuring result is not satis- factory, execute the measurement several times and judge the result from the synthetic point of view. Microwave output power should be within + 15% of the nominal one.
Calculation of output power;
Microwave output power ...P(W)=7Ox AT(%)
AT = ( ATL + ATR) / 2 : average temperature rise
ATL = (TL2 - TLI), ATR = (TR2 - TRI)
TL2 : water temperature after heating in left beaker
TLI : water temperature before heating in left beaker
TR2 : water temperature after heating in right beaker
TRI : water temperature before heating in right beaker
Measuring condition;
As the microwave output is affected by several conditions, the measurement should be made carefully with following attentions.
1.Initial temperature of salt water should be 10 + 1 “C. Well and quickly stir the water and the temperature measurement should be done immediately after heating.
2.The graduation of thermometer should be scaled by 0.1 “Cat minimum and an accurate mer- cury thermometer is recommended.
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