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

Rosemount 848L

Reference Manual

00809-0100-4696, Rev AA September 2004

Redundant Motors - Switch on Failure

Again, there are redundant pumps. There is a pressure switch in the common discharge line. If the pressure falls then the other pump is started. If the pressure does not recover, possibly because a flammable liquid is pouring on the ground from a broken pump housing, then the alternate pump is stopped. 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 pressure switch is linked into a DO that is true when the pressure is low.

	3	4		2		+-----	+	L1
+	--/	-----/-----			---	Set	------	( )--	+ EQ1
	1
+	--/	--+----------------				Reset
	T					+-----	+
+	--	--+
	DO							P
+	--^	--+-----------------------------						( )--	+ EQ2
	L1
+	--^	--+
	DO	L1						T
+	-- -----	------------------------						( )--	+ EQ4
	P	L2				+-----	+	L2
+	--^	----/------------				Set	------	( )--	+ EQ4
	P	L2
+	--^	---- ------------				Reset
						+-----	+
		L1		P		L2	Out2	Out1
+	---------	--	+--	--	+--	/---	/----	( )--	+ OUT1_EQ
				3
			+--	--	+
		L1		P		L2	Out1	Out2
+	---------	--	+--	--	+--	---	/----	( )--	+ OUT2_EQ
				4
			+--	--	+

Instantiate a DO block and set the channel number to 9.

E-14