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The controller then reads the reaction of these test signals on the
process. Keep in mind that every process is different and therefore
every reaction to the test signals is different. This is why PID parame-
ters are not the same for different processes. The amplitude (L) or lag
time which is the overshoot and undershoot of the system when auto-
tuning and the time constant (T) which is the time the process takes to
go through one On/Off cycle is measured. See diagram below.
The measurements are then used with the Autotune algorithm for cal-
culation of the proper PID parameters for the system. See the Autotune
algorithm below, where K is the proportionality constant and S is the
Laplace operator.
Time Constant
Time
OFF
Time
ON
Overshoot
Undershoot
Amplitude
K
e-LS
(1+TS)
