Garland CG-60, CG-24, CG-36 SERVICE BULLETIN #95-5, FROM - National Service Department, Subject

SERVICE BULLETIN #95-5

	FROM – National Service Department	BULLETIN NO.. #95-5
	TO – National Service Binder Holders	DATE – February 24, 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 2˚F to 4˚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 T2) 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
T1 junction	I			T2 junction
Metal B		V	Metal B	T = Temperature
	Figure 1			I = Current
				V = Voltage (emf)

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..

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