Filter
Top Products
Reference Manual
00809-0100-4696, Rev AA
September 2004
F-7
Rosemount 848L
Motorized Valve 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));
Heat Exchange Medium
Selection
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:
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));
Valve Output Opened Closed
Steam In Out1 In1 In5
Steam Out Out2 In2 In6
Water In Out3 In3 In7
Water Out Out4 In4 In8