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Unformatted text preview: circuit resistance. Which does not exceed 5 Ohms. The resistor connected across slave relay is used to absorb the coils self induced voltage thus to prevent arcing across points of sensitive relay. Contacts of sensitive relay are so fragile would burn or weld if arcing is permitted. When test switch is closed current flows through heater and heats up the test thermo couple. This cause current to flow to the thermo couple loops and fire warming light illuminate. Thermo couple is an electrical device consisting of a loop made of two different types of wire. A voltage is generated in a thermo couple i.e., is proportional to the difference in the temperatures of the two points where the dissimilar wires join this voltage difference causes current to flow. Thermo couples are installed around the area to be protected and one thermo couple is sounded by insulation that prevents its temperature from changing rapidly. In the event of fire the temperature of all thermo couples except thermally insulated one will raise i...
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