Panasonic SR-GA421, SR-GA281 service manual Center Thermostat, Switch-On Preventive System

SR-GA421/SR-GA281/SR-GA721

2. FUNCTION OF CENTER THERMOSTAT AND THERMALFUSE

A. Center Thermostat

The center thermostat senses when the bottom of the rice cooker pan reach 134°C ± 6°C. And it’s action turns off the cooking cycle, and starts the warming cycle.

Center thermostat construction
	Metal			Cook switch button
Magnet	Inner spring	Outer
	Cooking heater
	Rod Inner spring	spring	Switch lever
Figure 1			NC
	(Cooking Position)	(Warming or Off Position)		Micro switch
			C

Refer to these figures showing the center thermostat construction and cooking position. As the metal is heated, its ability to be attracted by the magnet decreases.

Finally, the inner spring pressure becomes stronger than the magnetic pull and the metal and magnet will pop apart. The rod activates the switch lever which causes the auxiliary lever to press the micro-switch button into the warming cycle.

B. Switch-On Preventive System
Metal	Thermostat surface
Cooking heater	Inner spring
	Outer spring
Magnet
	Thermostat case
10mm		Cook switch button
Rod	Switch lever	Auxiliary lever
		Micro switch

This is design to prevent the rice cooker from being turned on without the pan placed into position.

1)Normally when the pan is inserted properly into the rice cooker, the pan will depress the center thermostat. The center thermostat outer spring will be compressed. In this case when the switch button is depressed, the following will happen:

a.The auxiliary lever will release the micro-switch button. This puts the micro-switch in the cook position.

b.The switch lever will push the rod which will allow the magnet to meet with the metal.

c.When the rice is cooked and the proper temperature has been reached 134°C ± 6°C, the metal and magnet will pop apart as described in the center thermostat operation above.

d.The rod will push the switch lever and cause the auxiliary lever to depress the micro- switch button. This puts the micro-switch in the warming position.

2)When the pan is not in place within the rice cooker, the center thermostat is not depressed.

a.In this condition, the outer spring is not compressed within the center thermostat preventing the metal from reaching its normal operating position.

b.When the switch button is depressed, the switch lever and auxiliary lever work as above but the magnet cannot come in contact with the metal to hold the switch lever in the cook position. This happens because the switch lever hits the thermostat case and cannot push the rod, with the magnet attached, all they way up to meet with the metal.

c.When the pressure is taken off the switch button, the switch lever releases immediately to the open or warm positions.

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