Emerson manual Winding Temperature, Rosemount 848L, Reference Manual

Rosemount 848L

Reference Manual

00809-0100-4696, Rev AA September 2004

Winding Temperature

The multi-rung delay mechanism above may be replaced if the motor has a winding temperature sensor and a convertor that opens a contact when the motor is too hot and closes when it is sufficiently cool. The following drawing applies such a contact (as input 4) to the Restart Delay diagram, which reduces it to a permissive circuit.

	1		2	4	Out1
+--	--	+	------	--+----------------	( )--+ OUT1_EQ
			3
		+	----------	+

The equations for a permissive circuit have already been described.

•The expression is AND(IN(1),OR(AND(IN(2),IN(4)),IN(3));

NOTE

This is not an interlock for high winding temperature. That is taken care of by the overloads. The purpose of this circuit is to prevent starting if the motor is too hot, such that the heat generated by starting would exceed the temperature rating of the motor. When the motor starts, the temperature will rise and open the safe temperature contact. This will happen after the auxiliary contact has closed, so the motor will continue to run. As it runs, it is cooled by an internal fan and eventually the safe temperature contact closes. An interlock could be added, but the temperature would have to be set much higher than the safe restart temperature.

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