Garland MCO-GD-10M Service Manual

Contents

Garland MCO-GD-10M Service Manual Manual pdf 6 page image

6A thermocouple type test instrument is preferred for measuring oven temperatures accurately. Mercury thermometersare acceptable providing they can be proven accurate.Regardless of the type instrument used, it is most desirable to double-check it just before making an oven temperaturecheck. This can be done simply and quickly by placing the thermocouple tip (or immersing the entire mercurythermometer) in boiling water. Note: Mercury oven thermometers should be the "total immersion type." Theresulting reading should be within several degrees of 212°, -depending on the altitude.Generally, a mercury thermometer can drop in excess of 25° when the doors are opened to check oven tem perature.This condition makes it extremely difficult to get a true temperature reading.Almost all ranges today have oven burners which cycle "on and off." The high and low points of the resultingtemperature "swing" (differential) in the oven must be measured-and averaged-to determine the true operatingtemperature. A thermocouple type test instrument is best suited to measure these temperature changes quickly andaccurately, and without opening the oven door.With an accurate, thermocouple test instrument or mercury thermometer, it is still difficult to measure these changingoven temperatures and then, average them correctly. This is why we recommend that the thermocouple tip or the bulbof the thermometer be "weighted." Weighting (adding mass) to the test instrument compensates for oven temperaturechanges by making the test instrument less sensitive to these constant changes in temperature. Note: How thisweighting can be done is discussed later.Measuring these changing high and low temperatures points in an oven is possible with either type of test devicewithout weighting but is subject to possible inaccuracies. This is most true at low temperature setting because, in thisarea, the function of "time" becomes a factor. The simple averaging of temperatures, then, may not produce the trueoperating temperature. "Weighting" provides the compensation for both time and temperature that is necessary.We produced (next page) test curves showing actual results in the low temperature area showing the difference inresults when using an unweighted and a weighted thermocouple or thermometer. Tests were made with the samecontrol, same oven and dial at 170° mark (not move d).From the above, it can be seen that an error of 15° is possible. Chart #1, unweighted thermocouple indicates anerroneous average oven temperature of 185°. Chart #2, weighted thermocouple indicates the "average" or truetemperature to be 170°.WEIGHTINGA thermocouple can be weighted by clamping the tip between two one-inch squares of 1/16" thick aluminum. Thethermocouple can also be weighted (just as successfully) by using a letter-size sheet of aluminum foil. Fold the foilChart No.2Weighted Thermocouple Dial Setting 170F100120140160180200220240260Chart No.1Unweighted Thermocouple dial setting 170 F100120140160180200220240260