Dead-Band or Hysteresis in Control loops

Understanding Dead-band

• The following information may have errors; It is not permissible to be used by anyone who has ever met a lawyer. Use should also be confined to Engineers with more than 370 course hours of electronic engineering and should only be used for theoretical studies.

Dead-band is most easily understood as a 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 the (dead-band or hysteresis of the control loop).  Any digital controller can have 100% dead-band - older analog systems were sometimes limited in dead-band range.

 

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