Emerson manual Motorized Valve Heat Exchange Medium Selection, Rosemount 848L, Reference Manual

Reference Manual

00809-0100-4696, Rev AA September 2004

Rosemount 848L

Motorized Valve

Heat Exchange Medium Selection

The motor runs forward to open the valve and reverse to close it. When the motor is off, the valve cannot move. Both confirms are required. Output 1 causes the motor to run forward, Output 2 is reverse. Only one output must be active at a time. Input 1 confirms that the valve is open and input 2 confirms closed.

OUT1 contains AND(DO(1),NOT(IN(1)),NOT(EQ(2)));

OUT2 contains AND(NOT(DO(1)),NOT(IN(2)),NOT(EQ(2)));

The alarm interacts with the motor drive so that power is not applied after the travel time expires. This prevents burnout of small motors that do not have a motor starter. A crack time alarm is also used in case the valve is stuck. Since this works even for small motors, there is no point to making it optional. The crack time is 5 seconds in this example and the travel time is 30 seconds.

EQ1 contains TON(OR(AND(IN(1),IN(2)),AND(DO(1),IN(2)),AND(NOT(DO(1)),IN(2))),5 0);

EQ2 contains OR(TON(OR(AND(NOT(DO(1)),NOT(IN(2))),AND(DO(1),NOT(IN(1))),300 ),EQ(1));

The media are steam and chilled water. DO1 is on to select heating with steam and off to select cooling with water. All four valves have both confirms, as follows:

Valve	Output	Opened	Closed
Steam In	Out1	In1	In5
Steam Out	Out2	In2	In6
Water In	Out3	In3	In7
Water Out	Out4	In4	In8

Steam condensate must drain and both steam valves be closed before the water valves are opened. The water must drain and both water valves be closed before the steam valves are opened. There is a steam trap after the steam outlet valve to prevent steam from blowing through the heat exchanger. The opening of the steam outlet valve is delayed to allow some condensate to form in the exchanger for proper operation of the trap.

OUT1 contains AND(DO(1),IN(7),IN(8));

OUT2 contains TOF(TON(OUT(1), 1200),1800);

OUT3 contains AND(NOT(DO(1)),IN(5),IN(6));

OUT4 contains TOF(OUT(3),1600);

Heating is confirmed if In1 and In2 and In7 and In8 are on. Travel time must include the water drain delay time and the steam outlet opening delay. Cooling is confirmed if In3 and In4 and In5 and In6 are on. Travel time must include the steam drain delay time.

EQ1 contains TON(AND(NOT(DO(1)),NOT(AND(IN(3),IN(4),IN(5),IN(6)))),1900);

EQ2 contains OR(TON(AND(DO(1),NOT(AND(IN(1),IN(2),IN(7),IN(8))),2900),EQ(1));

F-7