Filter
Top Products
Reference Manual
00809-0100-4696, Rev AA
September 2004
Rosemount 848L
F-4
Open-Auto-Close Those applications that use a local switch with automatic control have a three
position switch arranged as Open-Auto-Close. Inputs 1 and 2 are used for
confirms, so input 3 is used for Open and input 4 for Closed. No input is
required for Auto.
• The Boolean expression is:
• The 848L expression is:
• EQ1 contains OR(AND(NOT(IN(4)),DO(1)),IN(3));
Alarm Variations If there is just one close confirm on input 2, then the Boolean expression is:
ALARM = TON ( ( !DO1 & !IN2 ) | ( DO1 & IN2 ), TravelTime)
If there is just one open confirm on input 1, then the Boolean expression is:
ALARM = TON ( ( DO1 & !IN1 ) | ( !DO1 & IN1 ), TravelTime)
It both confirms are used, then the Boolean expression is:
ALARM = TON ( ( !DO1 & !IN2 ) | ( DO1 & !IN1 ) | ( IN1 & IN2 ),
TravelTime)
The equivalent 848L expressions are:
TON(OR(AND(NOT(DO(1)),NOT(IN(2))),AND(DO(1),IN(2))),100);
TON(OR(AND(DO(1),NOT(IN(1)),AND(NOT(DO(1)),IN(1))),110);
TON(OR(AND(NOT(DO(1)),NOT(IN(2))),AND(DO(1),NOT(IN(1)),AND(IN(
1),IN(2))),120);
The chosen expression goes in the last expression used, which must be
linked to a DI to generate an alarm.
Output Variations A valve actuator may be spring return, requiring one output, or bistable,
requiring two outputs. Output 1 is used for Open and output 2 for Close.
Bistable valves often require a short pulse instead of maintained power. The
848L expressions for spring return are:
OUT1 contains DO(1);
or bistable has:
OUT1 contains TP(DO(1),30);
OUT2 contains TP(NOT(DO(1)),30);
Output with Interlock The interlock may be wired, or internal, or from the bus.
The example uses a DO from the bus:
OUT1 contains TP(AND(DO(1),DO(3)),30); spring return is
AND(DO(1),DO(3));
OUT2 contains TP(OR(NOT(DO(1)),NOT(DO(3))),30);