Garland CG-24 Service Manual - page 15

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