Emerson manual Simple Valve Variations Permissive, Rosemount 848L, Reference Manual

Reference Manual

00809-0100-4696, Rev AA September 2004

Rosemount 848L

Simple Valve Variations

Permissive

A spring return valve with one close confirm: EQ1 contains TON(OR(AND(NOT(DO(1)),NOT(IN(2))),AND(DO(1),IN(2))),100);

OUT1 contains DO(1);

The fourth similar spring return valve in the same 848L: EQ4 contains TON(OR(AND(NOT(DO(4),NOT(IN(8))),AND(DO(4),IN(8))),100);

OUT4 contains DO(4);

A bistable valve with both confirms and a local station:

EQ1 contains OR(AND(NOT(IN(4)),DO(1)),IN(3));

EQ2 contains

TON(OR(AND(NOT(DO(1)),NOT(IN(2))),AND(DO(1),NOT(IN(1)),AND(IN(

1),IN(2))),120);

OUT1 contains TP(DO(1),30);

OUT2 contains TP(NOT(DO(1)),30);

The second similar bistable valve in the same 848L:

EQ3 contains OR(AND(NOT(IN(8)),DO(2)),IN(7));

EQ4 contains

TON(OR(AND(NOT(DO(2)),NOT(IN(6))),AND(DO(2),NOT(IN(5)),AND(IN(

5),IN(6))),120);

OUT3 contains TP(DO(2),30);

OUT4 contains TP(NOT(DO(2)),30);

The permissive may be wired, or internal, or from the bus. The example uses DO3 from the bus. The confirmed open switch is used to hold the valve open if the permissive goes away. If the valve is spring return:

OUT1 contains AND(DO(1),OR(DO(3),IN(1)));

A bistable valve does not need a latch:

OUT1 contains TP(AND(DO(1),DO(3)),30);

OUT2 contains TP(NOT(DO(1)),30);

Either way, the alarm equation for just the open confirm is: TON(OR(AND(DO(1),NOT(IN(1)),AND(NOT(DO(1)),IN(1))),110);

The alarm equation for both confirms is: TON(OR(AND(NOT(DO(1)),NOT(IN(2))),AND(DO(1),NOT(IN(1)),AND(IN( 1),IN(2))),120);

F-5