Sensotec PIM-3, Manual, Page: 81 / 97

Model PIM-3 12-7
Now, we want the pump to run when the level drops to
500 gallons, and to remain on until the level gets to 2500
gallons. If we can drive a relay to run the pump, we would
like to energize the relay between 500 and 2500 gallons.
Notice that this would work exactly backwards to a normal
set of high-low limits, but we could drive the relay nor-
mally, and use the normally-closed contacts of the relay to
drive the pump. Putting the two limits outputs in parallel
as drivers to the relay would accomplish this. The 2500
gallon limit becomes a high limit (hysteresis is negative),
and the 500 gallon limit becomes a low limit (hysteresis is
positive).
Limit 2 Setpoint = 2500
Limit 2 Hysteresis = -150
Limit 3 Setpoint = 500
Limit 3 Hysteresis = 150
Figure 12-3 illustrates the setup, and Figure 12-4 shows
the required circuit.