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Reference Manual
00809-0100-4696, Rev AA
September 2004
Rosemount 848L
E-6
Restart Delay An off delay timer is required as a permissive for starting the motor. When the
motor is started, the off delay contact opens the circuit for the start button and
keeps it open for a specified time. The motor will be cooled as it runs, so the
delay is only applied to the start. Motors that require this are usually large and
have long cooling times, like 30 to 100 minutes.
| |
| 3 T |
+--||---------------------------------( )--+ EQ1
| |
| 1 2 T Out1 |
+--| |--+--||----|/|--+---------------( )--+ OUT1_EQ
| | | |
| | 3 | |
| +--||---------+ |
| |
Channels 1, 2, and 3 are the same as for basic motor control. T is the off
timer. Notice that this diagram depends on the order of execution of ladder
rungs. EQ1 is executed before OUT1_EQ. The value of EQ1 is initially false
because the motor is not running. The start button starts the motor. When the
confirm contact closes, EQ1 becomes true and breaks the start circuit, but the
confirm contact has closed and the motor stays running.
Each rung requires a separate equation in the 848L so that the execution
order can be preserved. Note that the output equations are always executed
last, so it is good practice to arrange the ladder diagram in execution order.
Rung T is equation 1. It generates a 60 minute pulse when the confirm
contact is true.
• The expression is TP(IN(3), 36000);
For rung Out1, the expression is basic motor control with input 2 in
series with T:
• The expression is AND(IN(1),OR(AND(IN(2),NOT(EQ(1)),IN(3)));