Model PD655 Large Display Process Meter
Instruction Manual
81
Pump Alternation Control
For pump control applications where two similar pumps are used to control the
level of a tank or a well, it is desirable to have the two pumps operate alternately.
This prevents excessive wear and overheating of one pump over the lack of use
of the second pump.
A pair of relays can be set up to alternate every time an on/off pump cycle is
completed. Set points and reset points can be programmed, so that first pump on
is the first pump off.
Pump Alternation Typical Application
Pump alternation setup
1. All relays are set up to respond to process/rate.
2. Relays 1 and 2 are set up to alternate.
3. Relays 3 and 4 are programmed for low and high alarm indication,
respectively.
Set and reset point programming
Set point 1
30.00
Reset point 1
10.00
Controls pump #1
Set point 2
35.00
Reset point 2
5.00
Controls pump #2
Set point 3
4.00
Reset point 3
9.00
Controls low alarm
Set point 4
40.00
Reset point 4
29.00
Controls high alarm
Pump alternation operation
1. Pump #1 turns on when level reaches 30.00, when level drops below 10.00
pump #1 turns off.
2. The next time level reaches 30.00, pump #2 turns on, when level drops
below 10.00 pump #2 turns off.
3. If the level doesn’t reach 35.00 pump #1 and pump #2 will be operating
alternately.
4. If pump #1 can’t keep the level below 35.00 pump #2 will turn on at 35.00,
then as the level drops to 10.00 pump #1 turns off, pump #2 is still running
and shuts off below 5.00.
5. With set and reset points of pump #2 outside the range of pump #1, first
pump on is the first pump to go off. This is true for both pumps.
