4-28
Chapter 4. Functions
Up to four loops can be controlled individually. Use the AT function to set the PID constants automatically.
z
How to start
(1) Make sure that the PV (analog input) and the actuators (heater power, etc.) are
ready for control.
(2) Make sure that this device is in RUN mode on the 1-loop monitor screen. If it
is in READY mode, change the mode to RUN.
(3) Make sure that the device is in AUTO mode on the 1-loop monitor screen. If
the device is in MANUAL mode, change the mode to AUTO.
(4) On the 1-loop monitor screen, press the
[
]
(mode) button, and press the
[START]
button in "AUTO TUNING."
z
How to stop AT
AT stops automatically after the PID constants have been set.
To stop AT while it is running, press the
[STOP]
button next to the AT graph on the
1-loop monitor screen. Alternatively, on the 1-loop monitor screen, press the
[
]
(mode) button, and press the
[STOP]
button in "AUTO TUNING."
Also, AT can be stopped by switching the mode to READY or MANUAL.
z
z
Display while AT is running
While AT is running, the AUTO TUNING progress graph is displayed on the
monitor screen. After AT ends and the PID constant is obtained, the AUTO
TUNING progress graph disappears.
z
z
Operation while AT is running
AT obtains the PID constants using the limit cycle.
(1) AT uses the limit cycle method to find the PID constants by making a 2:1
dividing point in the deviation between the SP and PV at the start of AT.
This point becomes the ON/OFF switching point for the MV (manipulated
variable).
(2) When it is determined that the limit cycle has stabilized, the PID constant is
changed, and AT ends.
PV
SP
2/3
1/3
Insufficient
stability
AT start
Time
Normal termination
Stable
cycle
4 - 5
AT (Auto-tuning)
