29
SRT Startup Condition
SRT will be ON if the following conditions are satisfied simultaneously when the
Temperature Controller is turned on or the set point is changed.
At the time the Temperature Controller
starts operating
At the time set point is changed
1) The set point at the time the
Temperature Controller starts operating
is different from the set point used at
the time SRT was last executed (see
note).
2) The difference between the set point
and the process value at the time the
Temperature Controller starts operating
is larger than the present proportional
band value (P) x 1.27 + 4.
3) The process value at the time the
Temperature Controller starts operating
is smaller than the set point in reverse
operation and larger than the set point
in normal operation.
1) The new set point is different from
the set point used at the time SRT
was executed last (see note).
2) The set point changing range is
larger than the present
proportional band value (P) x 1.27
+ 4.
3) The process value is in stable
condition before the set point is
changed.
4) A larger set point value is set in
reverse operation and a smaller
set point is set in normal operation.
Note The last SRT-executed set point is set to 0 before shipping and when changing
from advanced PID control to advanced PID control with fuzzy self-tuning.
In order to prevent overshooting, the step controlled amount must be imposed
continuously only while the present deviation is the same as or greater than the
value obtained from the proportional band (P)
1.27. The step control will not be
applied when the deviation becomes smaller than this value.
If the step control amount is applied before the maximum temperature slope (R)
is obtained, SRT will not renew any PID constant. If the proportional band ob-
tained from the R and L values that were measured before the imposition had
been completed is larger than the present proportional band, the PID constants
will be renewed because the measured value is in the direction towards the suit-
able proportional band value, and the set point at that time will be the SRT-
executed set point.
4-1-2 Disturbance Tuning (DT)
DT is used to measure the control waveform and adjust the PID constants when
the measured temperature becomes unstable. When there are control charac-
teristic changes after the PID constants are refreshed with SRT or when the PID
constants are not suitable to the object to be controlled because SRT was not
executed, the PID constants will be adjusted with DT.
If there is overshooting at the time the Temperature Controller restarts operating
after SRT has been executed, DT adjusts the PID constants so that the set point
response waveform will be as close as possible to the most ideal response wa-
veform after it is deemed that there has been a characteristics change in the con-
trol system.
Set point
Stable range (set to 15.0
°
C before shipping)
Measurement of
set point response
waveform
The set point response waveform
at the time the Temperature Con-
troller restarts operation will be
closer to the most ideal response
waveform.
PID before tuning
PID after tuning
Stability judge-
ment time
Imposition Completion
Condition of Step Control
Amount
PID Constant Refreshing
Conditions
DT at the Time of Operation
Start and Set Value Change
Fuzzy Self-tuning Operation
Section 4-1
