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Reference Manual
00809-0100-4696, Rev AA
September 2004
E-11
Rosemount 848L
Redundant Motors -
Alternate Start
Two motors drive two pumps in a redundant configuration. The control valve
that follows the pumps will just waste the energy of the second pump, possibly
damaging the valve, if both pumps on at the same time. There are times when
neither pump is required. When a pump is required, the pump that was not in
use last time should be started to equalize the wear on the pumps. The push
button controls are Stop (input 1) and Start (input 2). An auxiliary contact is
required from each starter (inputs 3 and 4).
| |
| 3 4 2 P |
+--|/|----|/|-----|^|-----------------( )--+ EQ1
| |
| P L +-----+ L |
+--||-----|/|------------|Set |------( )--+ EQ2
| P L | | |
+--||-----| |------------|Reset| |
| +-----+ |
| |
| 1 2 L Out2 Out1 |
+---------| |--+--||--+--|/|---|/|----( )--+ OUT1_EQ
| | 3 | |
| +--||--+ |
| |
| |
| 1 2 L Out1 Out2 |
+---------| |--+--||--+--| |---|/|----( )--+ OUT2_EQ
| | 4 | |
| +--||--+ |
| |
Rung P is equation 1. It generates the pulse that will toggle the latch. The
pulse comes from the RISE function.
• The expression is AND(NOT(IN(3)),NOT(IN(4)),RISE(IN(2)));
Rung L is equation 2. It latches on when L was false and unlatches when L
was true.
• The expression is RS(AND(EQ(1),NOT(EQ(2)),AND(EQ(1),EQ(2)));
Rung Out1 is output equation 1. This is basic motor control with additional
contacts.
• The expression is
AND(IN(1),OR(IN(2),IN(3)),NOT(EQ(2)),NOT(OUT(2)));
Rung Out2 is output equation 2. This is also basic motor control with
additional contacts.
• The expression is AND(IN(1),OR(IN(2),IN(4)),EQ(2),NOT(OUT(1)));