Dead-band hysteresis

Dead-Band or Hysteresis in Control loops

Understanding Dead-band

Dead-band is most easily understood by the example of the thermostat that keeps your house warm.

When it is cold the heat comes on until the house is warm at which point it stops (this is the stop point). Then, as time goes by, the house cools off and the furnace needs to restart - this would be the start point.


If the start and stop point are the same value, the furnace would go on and off every 30 seconds - causing wear and tear on the fan and wasting fuel. By spreading the start and stop point the furnace runs longer. The difference between the start and stop point is called the dead-band or hysteresis of the control loop). Most any digital controller can be set to have 0 to 100% dead-band - older analog systems were sometimes limited in dead-band range.

panel meters and PLCs can be set up to use dead-band or hysteresis control for controlling furnaces, pumps and more.

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