30
After the process value reaches the set point and becomes stable, if the process
value is disturbed and the disturbance exceeds the stable range, the distur-
bance is regarded as external disturbance At the time of disturbance, DT mea-
sures the external disturbance waveform and adjusts the PID constants so that
the external disturbance waveform will be as close as possible to the most ideal
external disturbance response waveform.
The external disturbance response waveform is approaching to
the most ideal response waveform even if the same kind of
external disturbance reoccurs. The waveform will not, however,
change if the most ideal PID constants are already set.
External disturbance
Set point
External disturbance
Stable range
(set to 15.0
°
C before shipping)
Measurement of
external disturbance
response waveform
PID after tuning
PID before tuning
Stability judge-
ment time
Startup Conditions of DT
DT is used to monitor the control waveform if there is external disturbance or
SRT does not work at the time the Temperature Controller starts operating or at
the time of set point change. If the measured waveform is not an ideal waveform,
DT will be ON. If either one of the following conditions is satisfied, the control
waveform will be monitored.
1, 2, 3...
1. SRT Startup conditions 3 and 4 on page 29 are satisfied but neither 1 nor 2 is
satisfied.
2. There has been an external disturbance exceeding the stable range after
the process value was in stable condition.
Note The stable range is set to 27
°
F with the E5
J-
-F.
4-1-3 Hunting Tuning (HT)
If there is hunting due to characteristics changes of the control system, HT is
used to measure the hunting waveform and adjust the PID constants to sup-
press the hunting.
Set point
Extreme value
Stable range
(set to 15.0
°
C before shipping)
Measurement of
hunting waveform
PID before tuning
PID after tuning
Startup Conditions of HT
HT will be ON when there is hunting with four or more maximum temperature
values while SRT is not being executed.
Note If the periodic temperature changes of the application exceed the stable range
(set to 15.0
°
C at the factory) due to continuous external disturbance (i.e., the
temperature is affected by an external disturbance before stabilizing after a pre-
vious external disturbance (refer to figure A below)), the user should change the
stable range to a value greater than the temperature changing range, otherwise
DT at the Time of External
Disturbance Response
Fuzzy Self-tuning Operation
Section 4-1
