Nor-Cal SDC15 Controller - Manual (Page 76)

5 - 6 Precautions for ST (Self-tuning)
5-26
Chapter 5. DETAILED DESCRIPTION OF EACH FUNCTION
When using the ST function, the following cautions must be observed strictly:
● Before starting the ST function, put the PV input and operation end (heater
power, etc.) in the controllable status.
● Before starting the ST function, set the PID constants so that the PID control
can be performed correctly.
• The default settings before shipment are that the proportional band [P-1] =
5.0%, integration time [I-1] = 120s, and derivative time [d-1] = 30s.
These default settings apply to the PID control of general control subjects.
• When the integration time [I-1] = 0s, the ST is not started.
• When the derivative time [d-1] = 0s, the ST is not started.
● To stop the control with the power to the controller kept turned ON, change the
mode to the READY mode and stop the operation at the operation end (turn
OFF the heater power). Additionally, to restart the control, start the operation
at the operation end (turn ON the heater power), and then change the mode to
the RUN mode.
Handling Precautions
• If any cautions described above are not observed, the PID constants
are changed to incorrect values when the ST is completed. This may
cause poor control results.
• When the power to the controller is turned OFF while the ST is
running (LED is flashing), the PID constants are not changed.
Additionally, if the power is turned OFF immediately before the ST is
completed, incorrect PID constant values are set.
If the PID constant values become incorrect, follow the steps below to reset them.
(1) Return the PID constants to their default values. (Make the settings so that
proportional band [P-1] = 5.0%, integration time [I-1] = 120s, and derivative
time [d-1] = 30s.)
(2) Start the ST, or set the PID constants using the AT function, and then start the
ST.
● Control subject of interference system
There are adjacent control subjects in the horizontal and vertical directions. Each
temperature change adversely affects the mutual ST functions and the response
latency of the control may be delayed. In this case, the unit is operated with the
control method set at “Fixed PID” ([CtrL] = 1).
● Control subject producing external disturbance intermittently
If the customer’s system produces the temperature drop intermittently, such as
sealing of the wrapping machine, this may affect the ST adversely.
In this case, the unit is operated with the control method set at “Fixed PID” ([CtrL]
= 1).
● Control subject producing external disturbance intermittently
When PV alarm occurrence and recovery are frequently repeated:
If PV alarm and recovery are frequently repeated while ST is running, it is judged
as a hunting. And the PID parameters may be changed. When this status happens
during instrumentation, set this unit to READY mode or set not to use the ST.