How To Eliminate Chatter on a Float Switch


Custom multi-point float switches need an external controller to add hysteresisConstant on-off cycling (chatter) in tank level pump control applications can add unnecessary wear and tear and lessen the life of a pump.

Chatter is usually seen in level control applications when there are single-point float switches and the liquid is turbulent or the level is changing rapidly. With only a single switch point, the rapid rising and falling of the level causes the switch to fluctuate the on and off state, causing pump chatter.

The way to solve this problem is to have two switch points (High and Low) such as with the FLE series of custom multi-point float switches, and add hysteresis between the switch points. Hysteresis can be added through the use of a powered pump control relay such as the RCU-7000.

Wiring the FLE sensor and pump to the RCU is done in only a few easy steps.

  1. Terminals 1 (NO), 2 (Common) and 3 (NC) are used to connect the pump.
  2. Both L1 (High Level) black wires are connected to Terminals 9 and 11 with one wire in each.
  3. Both L2 (Low Level) white wires are connected to Terminals 10 and 11 with one wire in each.
  4. Choose Empty Control (High) or Fill Control (Low) logic from the selector switch found on the front of the RCU-7000.
  5. Connect source voltage to terminals 5 and 6 (90-132 VAC) or 6 and 7 (180-264 VAC).

Here is an example of how hysteresis works to eliminate chatter with an FLE sensor and RCU-7000 and the above connections:

Application: Tank level to be kept full

Tank Height: 10 ft.

Full level: 8 ft.

Low Level: 1 ft.

When the liquid level is at 1 ft., the low level switch point is energized and the pump will start filling the tank with liquid. When the liquid reaches the full level, the second float switch will cause the pump to turn off. The pump will stay off until the liquid falls back to the low level switch point where the process will repeat.

This delay of the pump - not turning on until the liquid falls to the low level - is hysteresis.
Pump chatter is eliminated and the pump’s life is extended.

Contact us if you have any questions, or if you'd like to talk about hysteresis and float switches.

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