Emerson manual Redundant Motors - Timed Switch, Rosemount 848L, Reference Manual

Rosemount 848L

Reference Manual

00809-0100-4696, Rev AA September 2004

Redundant Motors - Timed Switch

Again, redundant pumps are used but only one pump runs at a time. The process runs for years without being shut down. The switch between pumps occurs at a time near the end of the useful life of the pump, usually several thousand hours. Stopping the old pump is delayed by a TOF while the other pump comes up to speed, which the control valve can handle. The push button controls are Stop (input 1) and Start (input 2). An auxiliary contact is required from each starter (inputs 3 and 4). The life time is measured in thousands of hours, so an external retentive timer with a display is used. Timing power comes from Out2, reset power from Out1 and the timed out contact comes in at channel 5.

Actually, this scheme is not practical unless the latches are non-volatile.

	2					+-----	+	L1
+	-- -------------------					Set	------	( )--	+ EQ1
	1
+	--/-------------------					Reset
						+-----	+
	5							P1
+	--^--------------------------------							( )--	+ EQ2
	P1	L2				+-----	+	L2
+	-- ----	/------------				Set	------	( )--	+ EQ3
	P1	L2
+	-- ----	------------				Reset
						+-----	+
	L1							Out1
+	--^--	+-----------------------------						( )--	+ OUT1_EQ
	P1
+	-- --	+
	3	Out1						Out2
+	-- --	+--/------------------------						( )--	+ OUT2_EQ
	4
+	-- --	+
	L1	L2		Out1				Out3
+	-- ----	/--	+	-- --	+--------------			( )--	+ OUT3_EQ
				3
			+	-- --	+
	L1	L2		Out1				Out4
+	-- ----	--	+--	--	+--------------			( )--	+ OUT4_EQ
				4
			+	-- --	+

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