C5-1
IM 34M06H62-02E
2nd Edition : June 2008-00
C5. Auto-Tuning Function
There are two types of auto-tuning, namely, dynamic auto-tuning, where the
module performs tuning automatically, and (normal) auto-tuning, where the
module performs tuning when instructed by parameters.
C5.1 Dynamic Auto-tuning
Dynamic auto-tuning is a control function where the module observes the movements of
the measured values and output values, and automatically determines the optimal PID
values when it begins operation or when hunting occurs in measured values.
It is especially useful when the characteristics of the controlled object are such that
normal auto-tuning is not feasible, as well as in situations where control is unstable when
the set point is changed.
Dynamic auto-tuning is a type of self-tuning. Dynamic auto-tuning begins calculating PID
values when the conditions for PID calculation (to be described later) become true. When
the conditions become no longer true, it ends the calculation and updates the PID values.
Sometimes, it may fail to obtain proper PID values due to external disturbances or other
factors. If it cannot obtain proper PID values using the measured results, it does not
update the PID values.
-
To use dynamic auto-tuning, set the Dynamic auto-tuning Enable (SELF) parameter
to “1: Enabled”.
- The following PID values are updated by dynamic auto-tuning: Proportional Band
(PB), Integral Time (TI) and Derivative Time (TD). The PID parameter group to be
updated is determined by the Current PID Number (PIDNO) parameter.
Dynamic auto-tuning operates when any of the following conditions for PID calculation is
true.
- The output scales out to OH after control begins (changing from “Stop” to “Run” in
automatic or cascade mode).
-
After changing a set point, the output scales out to OH.
-
PV input oscillates more than 2
C for temperature input or 0.5% of PV input range for
DC voltage input due to external disturbances, etc.
Figure C5.1 PID Calculation Method
TIP
- Even during dynamic auto-tuning, control computation is carried out using current PID values that are
defined. In situations where the control output does not scale out to OH, current PID values may not
be changed automatically.
- In situations where stable control is achieved with PID values calculated using dynamic auto-tuning,
disabling dynamic auto-tuning can avoid inadvertent changes to the PID values due to external
disturbances or other factors.
- Executing auto-tuning during dynamic auto-tuning terminates the calculation of PID values in
dynamic auto-tuning. If the condition for PID calculation is again true after auto-tuning ends, dynamic
auto-tuning restarts PID calculation.
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Страница 215: ...C8 1 IM 34M06H62 02E 2nd Edition June 2008 00 C8 Alarm Function This chapter describes the alarm function of the module...
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