Description of the Firmware
IP244
C79000–B8576–C860–02
4–20
1.2.3 Calculated Parameters
Following the process identification, the self-tuning function calculates the controller parameters
sampling time (T
A
), controller gain (K
P
), integral action time (T
N
), derivative action time (T
D
) upper
and lower control zone (ZONOB, ZONUN) and with 3-step controller, the heating-cooling ratio
(HCR) or a separate parameter set for cooling.
In 3-step controllers, the self-tuning function calculates the lower limit of the control zone while
heating and the upper zone limit while cooling. The zones can therefore be asymmetrical. In 2-step
controllers, the upper limit is set to match the lower limit and the control zones are therefore
symmetrical. After they have been calculated, the parameters are entered in messages.
Criteria for calculating the parameters:
T
A
: longest sampling time at which a control quality less than 1
is achieved
K
P
, T
N
, T
D
: for good disturbance response at the operating point
ZONOB, ZONUN: for good response when large setpoint changes occur
HKV: for an operating point in the range from 100 C (only in 3-step
controllers)
Since individual parameters are optimized for the operating point, it is advisable to execute the
heating procedure until the temperature approaches the operating point.
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