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Reference Manual
00809-0100-4696, Rev AA
September 2004
Rosemount 848L
E-12
Redundant Motors -
Timed Switch
Again, redundant pumps are used but only one pump runs at a time. The
process runs for years without being shut down. The switch between pumps
occurs at a time near the end of the useful life of the pump, usually several
thousand hours. Stopping the old pump is delayed by a TOF while the other
pump comes up to speed, which the control valve can handle. The push
button controls are Stop (input 1) and Start (input 2). An auxiliary contact is
required from each starter (inputs 3 and 4). The life time is measured in
thousands of hours, so an external retentive timer with a display is used.
Timing power comes from Out2, reset power from Out1 and the timed out
contact comes in at channel 5.
Actually, this scheme is not practical unless the latches are non-volatile.
| |
| 2 +-----+ L1 |
+--| |-------------------|Set |------( )--+ EQ1
| 1 | | |
+--|/|-------------------|Reset| |
| +-----+ |
| 5 P1 |
+--|^|--------------------------------( )--+ EQ2
| |
| P1 L2 +-----+ L2 |
+--| |----|/|------------|Set |------( )--+ EQ3
| P1 L2 | | |
+--| |----| |------------|Reset| |
| +-----+ |
| L1 Out1 |
+--|^|--+-----------------------------( )--+ OUT1_EQ
| | |
| P1 | |
+--| |--+ |
| |
| 3 Out1 Out2 |
+--| |--+--|/|------------------------( )--+ OUT2_EQ
| | |
| 4 | |
+--| |--+ |
| |
| L1 L2 Out1 Out3 |
+--| |----|/|--+--| |--+--------------( )--+ OUT3_EQ
| | | |
| | 3 | |
| +--| |--+ |
| |
| L1 L2 Out1 Out4 |
+--| |----| |--+--| |--+--------------( )--+ OUT4_EQ
| | | |
| | 4 | |
| +--| |--+ |
| |