Emerson manual Rosemount 848L, Reference Manual, 00809-0100-4696,Rev AA September

Reference Manual

00809-0100-4696, Rev AA September 2004

Rosemount 848L

Rung L1 is equation 1. It latches on when the start button is true and neither motor is running. It unlatches when the NC stop button is pushed or the pressure stays low for too long.

•The expression is RS(AND(NOT(IN(3)), NOT(IN(4)),IN(2)),OR(NOT(IN(1)),EQ(3));

Rung P is equation 2, which generates a 2 second start pulse from the rise of the run latch or the rise of the low pressure condition. This pulse toggles the latch and starts the selected motor.

•The expression is TP(OR(RISE(DO(1)),RISE(EQ(1))),20);

Rung T is equation 3, which is a TON that is run by the on state of the low pressure and the run latch.

•The expression is TON(AND(DO(1),EQ(1)),100);

Rung L2 is equation 4. The latch determines which motor to start and run. It toggles when equation 2 generates a pulse. The pulse duration is more than one evaluation cycle, so rise functions are required.

•The expression is RS(AND(RISE(EQ(2)),NOT(EQ(4))),AND(RISE(EQ(2)),EQ(4)));

Rung Out1 is output equation 1. This is basic alternate motor control.

•The expression is AND(EQ(1),OR(EQ(2),IN(3)),NOT(EQ(4)),NOT(OUT(2)));

Rung Out2 is output equation 2. This is also basic alternate motor control.

•The expression is AND(EQ(1),OR(EQ(2),IN(4)),EQ(4),NOT(OUT(1)));

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