1.6
MS-2102
Chapter 1
Product Overview
On/Off Control with Deadband
The default control mode of the controller is deadband
control or simply on/off control with the proportional
control setting turned off. On/off control without
deadband (that is deadband set to 0 C° or 0 F°; note that
these units denote the temperature differential with “°”
placed to the right of the unit) means that the heater turns
on when actual temperature is below setpoint and turns
off when above setpoint. However, this causes
oscillations when the actual temperature is very close to
setpoint. To eliminate oscillations, hysterisis is applied to
the on/off control by a deadband value. The on/off
control with deadband operation is described by the
hysterisis curve in figure 1.4. Assume that actual
temperature is well below (setpoint - deadband setting),
the controller calls for heat. As the actual temperature
rises, the controller continues to call for heat until the
actual temperature has reached (se deadband
setting). The controller no longer calls for heat and the
heater is off. As the actual temperature cools, the
controller does not call for heat until the actual
temperature reaches (setpoint – deadband setting). The
hysterisis effect is controlled by the momentum of the
actual temperature rather than the temperature value itself.
Figure 1.4
On/Off Control with Deadband
