33
self-tuning will not be activated if the temperature is stable because the Temper-
ature Controller deems that temperature control is smooth.
Set point
Stable range
Stable range
(Set to 15.0
°
C before shipping)
Stable
Stable
Shorter than the stability judgement time.
Stability judgement time
Note The stable range is set to 27
°
F with the E5
J-
-F.
4-3-2 Hunting
If the PID constants are not suitable to the controlled device, the measured value
will fluctuate and will not coincide with the set point, this phenomenon is called
hunting. Hunting is also called cycling.
Set point
Set point
4-3-3 Characteristics and Characteristics Change
The angle of the maximum temperature slope (R) of the controlled device (i.e.,
whether the temperature rise of the device is fast or slow) and the dead time (L)
of the controlled device (i.e., how fast the change in the output of the Tempera-
ture Controller influences the temperature) vary with the characteristics of the
controlled device. The PID constants must be set according to the characteris-
tics of the controlled device. A characteristics change is the change of the char-
acteristics of the controlled device due to the change of its thermal capacity and
the change of the supply voltage. If there is a characteristics change, the PID
constants must be adjusted according to the new characteristics.
4-3-4 External Disturbance
External disturbance is an external factor that disturbs the temperature that has
been stable within the most ideal PID constants for the controlled device.
4-3-5 Interference
If devices, such as heaters, controlled by different temperature controllers are
physically close to one another, the heaters are mutually influenced and the tem-
perature of each heater are affected. This phenomenon is called interference. If
there is serious interference, it will be difficult for each temperature controller to
control the device, and special controlled methods taking this interference into
consideration will be required.
Terminology
Section 4-3
