3.7Executing ON/OFF Control
E5GN
3–11
3.7 Executing ON/OFF Control
In ON/OFF" control, the control output turns OFF when the currently
controlled temperature reaches a preset set point. When the manipulated
variable turns OFF, the temperature begins to fall and the control output
turns ON again. This operation is repeated at a certain point. At this time,
how much the temperature must fall before control turns ON again is
determined by the hysteresis (OUT1)" parameter. Also, how much the
manipulated variable must be adjusted in response in the increase or
decrease in the process value is determined by direct/reverse operation"
parameter.
Ă• Switching between 2ĆPID control and ON/OFF control is carried out by
the PID / ON/OFF" parameter (initial setting level). When this paramĆ
eter is set to ", 2ĆPID control is selected, and when set to ",
ON/OFF control is selected. Default is ".
Ă• In ON/OFF control, the hysteresis is used as a differential for switching
the output ON when the temperature moves away from the required set
point, and is used to give stability around the set point.
Ă• The hysteresis width is called the hysteresis band." The control output
(OUT1) function is set by hysteresis (OUT1)."
Ă• In standard control (heating or cooling control), the hysteresis
(OUT1)" setting is used as the hysteresis setting in the adjustment level
regardless of the control type, heating control or cooling control.
Set point
Hysteresis (OUT1)
ON
OFF PV
Reverse operation
Ă• In heating and cooling control, a dead band (an area where both control
outputs are 0") can be set to either the heating or cooling side. So,
3Ćposition control is made possible.
Set point
Hysteresis (OUT1)
Heating
side
Dead band
Hysteresis (OUT2)
Cooling
side
ON
OFF
PV
JON/OFF control
F Hysteresis
F 3-position
control
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