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Reference Manual
IP2030/RM, Rev AA
Section 4: Getting started
June 2014
Section 4: Getting started76
Duty Assist with split off points
This function requires two or more Assist mode relays. Two or more of these relays can be
energized at the same time (assisting), and they all de-energize at a split off points.
An Assist relay uses its On Point and Off Point parameters in a similar way to a Set Point mode
relay. A typical application would be emptying a wet well / lift station.
The worked example here illustrates how the function works. To keep the example simple, the
auto-sequencing options are not considered.
Example wet well / lift station application (emptying operation due to rising level)
using assist mode relays and split (separate) off points
Consider an application with two relays, RL1 and RL2, connected to individual pumps in a
wet well. The control unit PV value (D800) is a liquid level measurement in metres.
In Figure 4-32, both Pump 1 and Pump 2 are off because the liquid level is at a
satisfactory level, below 5 m
When the level exceeds 5 m (On Point, P411), relay RL1 is energized to start Pump 1
(Figure 4-33)
When the level exceeds 8 m (On Point, P421), relay RL2 is energized to start Pump 2 and
assist Pump 1. Relay RL1 stays energized to keep Pump 1 pumping (Figure 4-34)
When the level falls to below 3.5 m (Off point, P422), relay RL2 de-energizes to switch
off Pump 2 (Figure 4-35)
When the level falls to below 2 m (Off point, P412), relay RL1 de-energizes to switch
off Pump 1
Note
If Pump 1 keeps the level below 8 m, it would stay switched on until the level is 2 m.
Safeguards to prevent overuse of pumps are in “Relay safeguard options” on page 71
Figure 4-32. Both Pump 1 and Pump 2 are off (the level is okay)
5.0 m (P411)
8.0 m (P421)
3.5 m (P422)
2.0 m (P412)
Level in m
Pump 1
Pump 2