YOKOGAWA UT130, Техническая информация

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6-2
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TI 05C01E02-01E 1st Edition : Oct. 31, 2001-00
6.2 Proportional (P) Action
6.2.1 Differences between ON/OFF Action and Proportional Action
•
The proportional band is the parameter
that determines the effectiveness of
proportional action.
•
The figure on the left shows a
proportional action by comparison to the
simplest control action: ON/OFF action.
•
Differences between ON/OFF Action and Proportional Action
Control output
(reverse action)
Offset
(steady-state
deviation)
Control
performance
ON/OFF action Proportional Action
-Deviation +Deviation
Measured
temperature
Measured
temperature
Prone to oscillation
-Deviation +Deviation
No intermediate state
None
SP SP
100(%)
Output
0
100(%)
Output
0
0 0
(Fully open)
(Fully closed)
Output varies continuously in proportion
to amount of deviation.
A steady-state deviation (offset) between
measured temperature and setpoint is
inherent to the operating principle.
SP
Offset
Smooth control performance
SP
6.2.2 Proportional Band (P) Details
•
"Proportional band" is defined as the
amount of change* in input (or
deviation), as a percent of span, required
to cause the control output to change
from 0% to 100%.
•
Because a narrower proportional band
gives greater output change for any
given deviation, it therefore also makes
the control performance more
susceptible to oscillation. At the same
time, a narrower proportional band
reduces the offset.
•
Reducing the proportional band to its
smallest limit (proportional band = 0%)
results in ON/OFF control. UT100 series
controllers select ON/OFF control using
the parameter "CTL".
•
Note that the unit of proportional band
is the percent of PV input span, or actual
temperature in engineering units. For
UT100 series, set the actual
temperature.
Proportional band (P)
SP
Deviation
100(%)
Output
(Reverse action example)
0(%)
Proportional band
Total span
P=100%
(ON/OFF)
P=50%
P=0%
SP
Deviation
Output (%)
Wide proportional band
SP
Deviation
Output (%)
Narrow proportional band
Output =
P
100
e
P : Proportional band
e : Deviation