Garland CG-24, Service Manual

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Part #GCGTRAINING06 (03/03/08) Page 15
Tables of millivolt values for degrees Fahrenheit (at reference junction temperature 3˚) and
Centigrade (at reference junction temperature 0˚) have been written and extracts from these
tables form part of this bulletin . These are required if service technicians need to check a
thermocouple without a J calibrated temperature meter .
Check the thermocouple if you find the temperature variation of the thermostat is more than ±
5˚F from the set point . To check a thermocouple, follow this procedure:
Note: The Type J thermocouple requires the use of a Type J temperature meter .
If a type J meter is not available use a millivolt meter and refer to the tables of
degrees/millvolt values following, to calculate the cold junction compensation .
Remember that the accuracy of you measurements can be no more accurate than your
instruments . Thermocouples generate very small voltages . Many voltmeters cannot read
millivoltages accurately .
Set all control thermostats to the same temperature (350˚F) . Allow the griddle plate to saturate
and achieve a steady temperature .
Place a surface temperature probe on the griddle surface about the thermocouple you want to
check . The surface must be cleaned before this procedure . If there is any grease residue on the
probe or griddle plate, it will introduce an error in your reading .
Take the temperature reading of the plate above the controlling thermocouple .
Disconnect the thermocouple from the temperature and, either connect it to a J type calibrated
temperature meter to measure the temperature output directly or, do the following: measure
and record the millivolts generated by the thermocouple . Measure the ambient temperature .
Refer to the table and add the corresponding millvoltage for the ambient temperature to the
value measured from the thermocouple . Find the corresponding temperature in the chart for
millvoltge result .
Example:
if the ambient room temperature is 0˚ C add the millvolt value of
0˚C (1 .019mV) from the chart to the millvolt reading of the meter and find the
temperature value in the chart . The temperature should match the reading on
the surface of the plate .
SERVICE BULLETIN #95-5 continued