YOKOGAWA UP35A, User Manual

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8-10
IM 05P02D41-01EN
8.2.2 ON/OFF Control (1 point of hysteresis / 2 points of hysteresis)
Description
ON/OFF control compares the SP and PV and outputs an on or off signal according to
the positive or negative deviation (PV – SP). Hysteresis can be set in the vicinity of the
on/off output operating point.
If the SP and PV become close and the polarity of the deviation reverses frequently,
the on/off output will cycle repeatedly. The life of the output relay will therefore be
dramatically shortened.
In such a case, set a wider hysteresis so that the relay’s frequent on/off output (chattering)
will not occur.
When the control type (CNT) is set to “ONOF,” one point of hysteresis can be set to the
operating point.
When the control type (CNT) is set to “ONOF2,” two points of hysteresis (deviation
positive hysteresis and deviation negative hysteresis) can be set to the operating point.
1 point of hysteresis
Hysteresis
SP
Control
output
ON
ON
OFF
OFF
ON ON
OFF
PV
PV
Hysteresis
SP
Control
output
(Example of reverse action)
Temperature
2 points of hysteresis
HY.UP HY.LO
SP
Control
output
ON
ON
OFF
OFF
ON ON
OFF
PV
HY.UP
HY.LO
SP
Control
output
(Example of reverse action)
Temperature
PV
8.2 Setting Control Type (CNT)