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Using ON/OFF Control Section 3-7
3-7 Using ON/OFF Control
In “ON/OFF” control, the control output turns OFF when the currently con-
trolled temperature reaches a preset set point. When the manipulated variable
turns OFF, the temperature begins to fall and the control turns ON again. This
operation is repeated at a certain point. At this time, how much the tempera-
ture 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.
3-7-1 ON/OFF Control
• Switching between 2-PID control and ON/OFF control is carried out by the
“PID ON/OFF” parameter (initial setting level). When this parameter is set
to “pid”, 2-PID control is selected, and when set to “onof”, ON/OFF con-
trol is selected. Default is “onof”.
Hysteresis • With ON/OFF control, hysteresis is used to stabilize operation when
switching between ON and OFF.
The control output (OUT1) and control output (OUT2) functions are set in
the hysteresis (OUT1) and hysteresis (OUT2) functions respectively.
• In standard control (heating or cooling control), the setting of the “hystere-
sis (heating)” parameter in the adjustment level is used as the hysteresis
regardless of whether the control type is heating control or cooling con-
trol.
3-position control • In heating/cooling control, a dead band (an area where both control out-
puts are “0”) can be set to either the heating or cooling side. This makes it
possible to use 3-position control.
Set point
Hysteresis (OUT1)
ON
OFF PV
Revers operation
Set
oint
Hysteresis (OUT1)
Heating
side
Dead band
Hysteresis (OUT2)
Cooling
side
ON
OFF
PV
Revers operation
Symbol Parameter Name: Level Description
s-hc Standard or heating/cooling: Initial setting level For specifying control method
cntl PID ON/OFF: Initial setting level For specifying control method
orev Direct/reverse operation: Initial setting level For specifying control method
c-sc Cooling coefficient: Adjustment level Heating/cooling control
c-db Dead band: Adjustment level Heating/cooling control
hys Hysteresis (OUT1): Adjustment level ON/OFF control
chys Hysteresis (OUT2): Adjustment level ON/OFF control
Parameters
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