Omron CJ Series Operation Manual page 27

Introduction and Features
4
ness in this design was that both responses could not be satisfied at the
same time.
1. If the disturbance response were emphasized (i.e., P and I were re-
duced and D was increased), the SV response would oscillate and
overshoot.
2. If the SV response were emphasized (i.e., P and I were increased and
D was reduced), the disturbance response would be delayed.
To overcome these problems, PID control with two degrees of freedom was
used for this Temperature Control Unit to take advantage of the strengths
of PID control and improve both disturbance and target response as shown
in 3, below.
■ Earlier PID Control Method
1
The disturbance response is good, but
the SV response is delayed.
■ PID Control with Two Degrees of Freedom
3
Both the SV response and disturbance
response are good.
■ Autotuning (AT) Function
The Temperature Control Unit is equipped with an autotuning (AT) function
that uses the "limit-cycle method" to calculate the optimum PID constant for
the controlled system. (The SV cannot be written for a loop if the loop is being
autotuned.)
SV
2
The SV response is good, but the
disturbance response is not.
Hunting period
AT starts.
AT stops.
Section 1-1
Amplitude