Section 3 Basic Operations
3-10
Basic
Oper
ations
■
ST (Self-tuning)
ST (self-tuning) is a function that finds PID constants by using step
response tuning (SRT) when Controller operation begins or when the
set point is changed.
Once the PID constants have been calculated, ST is not executed
when the next control operation is started as long as the set point
remains unchanged.
When the ST function is in operation, be sure to turn ON the power
supply of the load connected to the control output simultaneously
with or before starting Controller operation.
●
Startup
Conditions
Self-tuning by step response tuning (SRT) is started when the
following conditions are met after program execution is started and
the set point is changed.
At start of operation
When set point is changed
1.
The set point at the start of
operation differs from the set point
when the previous SRT was
executed. *1
1. The set point after changing differs
from the set point when the
previous SRT was executed. *1
2.The difference between the
temperature at the start of
operation and the set point is
greater than both the following:
(Present proportional band
×
1.27 + 4
°
C) and the ST stable
range.
2. The set point change width is
greater than both of the following:
(Present proportional band
×
1.27
+ 4
°
C) and the ST stable range.
3.
The temperature at the start of
operation is lower than the set
point during reverse operation, and
is larger than the set point during
direct operation.
3. During reverse operation, the new
set point is larger than the set point
before the change; and during
direct operation, the new set point
is smaller than the set point before
the change.
4. There is no reset from input errors.
4. The temperature is stable. *2
(Equilibrium with the output
amount at 0% when the power is
turned ON is also all right. *3
*1.
The previous SRT-implemented set point is the set point that was
used for calculating the PID constants for the previous SRT.
*2.
In this state, the measurement point is within the ST stable range
.
*3.
In this state, the change width of the PV every 60 seconds is
within the ST stable range or less.
When auto-tuning (AT) is executed, PID constants are not changed by
self-tuning (ST) for the present set point.
Summary of Contents for E5CS-U
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