Heat Manager Pro User Manual V1.5 Page 71
B.4
A
UTO TUNING
It is also possible to make use of the auto tuning feature in the Heat Manager. This is only
possible when the controller is in a soak/dwell segment and the set value does not change over
time.
After enabling this feature the controller will perform a few test-cycles where it automatically
tries to determine the PID settings based on so-called step-wise changes of the set value.
After changing the controller output to maximum (or minimum) monitors the physical behavior of
the process value and determines the settings based on oscillation amplitude and period.
After performing many tests with various control systems, Ziegler and Nichols, derived formulas
on how to convert the results of these tests into PID settings as a starting-point before actual
fine tuning can take place.
It sometimes takes a while before the system actually determines the new values during this
auto tuning cycle. Please be patient and wait until you see the newly determined values appear.
This can take some minutes and depends on how quickly the process reacts to the controller.
If the controller was not able to determine the new values it will leave the PID settings on the
values before the start of the auto tuning procedure.
Watch out
: these calculated PID values are only a rough indication of the actual perfect PID
settings and
–can- result in an unstable process, so keep in mind that manual
fine tuning is often necessary.
Important:
only perform auto tuning when the process reached a stable state (controller
output and process value more or less stable). The set value must also be stable,
so this is only possible in a soak segment and not in a ramp up/down segment.
Warning:
Never execute an auto tuning procedure when the process conditions are not
stable. The software algorithm
assumes
that all external factors with regard to
the process are not changing while performing this operation.
Please remember, that a manually tuned controller almost always outperforms a controller that
was set with auto tuning. Auto tuning is more or less a rough indication if you need some
“direction” on where to start.
B.5
W
RITE DOWN THE NEWLY DETERMINED
PID
VALUES
!
It is very important, that you write down the newly determined PID values s
o you don’t lose
these painstakingly difficult to determine values.
A software upgrade, re-init procedure or controller module re-init (necessary after a
replacement) will restore the PID values back to their default values as programmed in the
software of the Heat Manager.
