YOKOGAWA UT55A User Manual

8-81
IM 05P01C31-01EN
Control Functions
8.2.6 SamplePIControl(ControllingaProcesswithLongDeadTime)
Description
Sample PI control performs PI control for a sample PI sampled time (STM) only during
the first sample PI control time span (SWD). It subsequently holds a control output when
that time elapses.
This control is useful for processes with long dead times where the results of the control
output
arenot
quicklyreflectedonPV.
Point A (where control starts)
↑
SP
OUT
Time
STM
SWD
STM
PV
Output held
Integral action
P+I
Output held
whereOUT:controloutput,SP:targetsetpoint,andPV:measuredinput
Action of Sample PI Control (S-PI)
To reduce overshoots, it is better to lengthen the sample PI sampled time (STM). This
results however in the settling time becoming longer.
If the shortest cycle (TN) of the main disturbance imposed on process is smaller than
the sample PI sampled time (STM), that disturbance cannot be controlled. A guideline is
approximately
STM≤
TN/5.
STM is reset by control start (AUTO and RUN.)
Control starts from the point A when:
● Operationmode
isswitchedfromSTOPtoRUN,
● OperationmodeisswitchedfromMANtoAUTO,
● Inputhasrecoveredfromburnout,
● OutputtrackingflagisswitchedfromONtoOFF.(Ladderprogramused),or
● Poweristurnedon.
* If the sample PI sampled time (STM) or sample PI control time span (SWD) is
changed, the operation is continued by the changed value immediately.
8
8.2SettingControlType(CNT)

YOKOGAWA UT55A Specifications

General

Brand	YOKOGAWA
Model	UT55A
Category	Temperature Controller
Language	English