Garland CG-24 Service Manual - Service Bulletin #95-5

Part #GCGTRAINING06 (03/03/08))

Page 1

SERVICE BULLETIN #95-5

FROM – National Service Department

BULLETIN NO . #95-5

TO – National Service Binder Holders

DATE – February , 1995

Subject: 

Subject: Thermocouples used in the Chain Griddle  

Models CG-36, CG-48, CG-60 & CG-72

This bulletin supplements the chain Griddle Service Manual with a description of the basics of 

thermocouple theory and how to use the degree/millivolt tables issued as part of this bulletin . 

This bulletin deals with the thermocouple only and how it registers temperature changes .

The type J thermocouple on the new Chain Griddle measures the plate temperature within a 

range of accuracy of ˚F to ˚F . The J designation refers to the conductors used and, therefore, the 

thermoelectric characteristics of the conductors that form the thermocouple . In the Type J unit, 

the conductors are iron and the alloy constantan . Constantan is an alloy of copper and nickel . 

Thermocouple technology for sensing temperature has been in use for a long time but the Type J 

thermocouple is new to Garland Commercial Ranges Limited applications .

To dissimilar metals joined together, as in Figure 1, cause a thermoelectric current to flow in the 

circuit formed when the junctions are at different temperatures . The current will continue to 

flow as along as the junctions (T1 and T) remain at different temperatures . Thermoelectricity 

is the direct conversion of heat into electricity and vice versa . The electric motive force (emf) 

producing the current is called the “Seebeck Thermal Emf” (Seebeck after the discoverer), and is 

proportional to the temperature difference between the two junctions .

Three laws govern the way thermocouples work: the law of homogeneous circuits, the law of 

intermediate metals and the law of successive or intermediate temperatures . The first law is that 

a thermocouple circuit must use different metals; the second is that a third metal introduced 

will not affect the couple provided it is maintained at the same temperature along its entire 

length; the third provides a means of relating the emf generated to a standardized constant 

temperature . Refer to a textbook about thermocouples for a fuller explanation of these laws .

Metal A

T

1 junction

T

2 junction

T  = Temperature

I  = Current

V  = Voltage (emf)

Metal B

Metal B

Figure 1

V

I

If the cold junction is at a known or reference temperature it is a simple matter to compare this 

with the hot junction at the probe of the thermocouple to obtain an accurate measure of the 

hot junction temperature . In practice, the cold junction is eliminated by the use of electrical or 

hardware compensating methods .