Installation manual

Introduction
900M050U00  Athena Controls, Inc. 1-9
1.5.3 On/Off Control
On/off control has two states, fully off and fully on.
On/off control can be used where:
• process is underpowered and has very little heater storage capacity
• some temperature oscillation is permissible
• electromechanical systems (compressors) make rapid cycling undesireable
To prevent rapid cycling, the controllers allow you to configure a deadband and a
hysteresis value for on/off control.
1.5.3.1 Use of Hysteresis
If you are using a single output for control, then use the hysteresis parameter to reduce
frequency of cycling.
The hysteresis value represents a temperature value that the controller uses to separate
the on and off transitions of the individual outputs. (You configure the Output 1 and
Output 2 hysteresis values independently.)
For example, in the diagram below, the setpoint is 100 and the hysteresis value is 10. In
this case the output would be on from startup until the process value reaches 105 (the
setpoint plus half the hysteresis value). After overshoot, the PV falls, but the controller
does not turn the output on again until the temperature falls to 95 (the setpoint minus half
the hysteresis value).