C200 SOFTWARE
Instruction Manual C200 Part2 A1.doc
optek Danulat GmbH • D-45356 Essen • Germany
page 110
B3 Setting Up Three Term (PID) Control Parameters
To enable a process to be controlled satisfactorily, the following conditions must apply:
a) The process must be capable of reaching a natural balance with a steady load.
b) It must be possible to introduce small changes into the system without destroying either the process or the product.
The
Proportional Band determines the gain of the system. (the gain is the reciprocal of the proportional band setting, e.g.
a setting of 20% is equivalent to a gain of 5). If the proportional band is too narrow, the control loop may become
unstable and cause the system to oscillate. With proportional band control only, the system normally stabilizes
eventually but at a value which is offset from the set point.
The addition of
Integral Action Time removes the offset but, if set too short, can cause the system to go into oscillation.
The introduction of
Derivative Action Time reduces the time required by the process to stabilize.
B4 Manual Tuning
Before starting up a new process or changing an existing one:
a) Select the
Config. Control page and ensure that Controller is set to PID – see Section 5.7.
b) Select the
PID Controller page and set the following:
Proportional Band – 100%
Integral Time – 0 (off) – see Section 5.7.1
Derivative Time – 0 (off)
Notes.
• If the system goes into oscillation with increasing amplitude (Fig. B4 Mode B), reset the proportional band to
200%. If oscillation continues as in Mode B, increase the proportional band further until the system ceases to
oscillate.
• If the system oscillates as in Fig. B4 Mode A, or does not oscillate, refer to step c).
c) Reduce the
Proportional Band by 20% increments and observe the response. Continue until the process cycles
continuously without reaching a stable condition (i.e. a sustained oscillation with constant amplitude as shown in
Mode C). This is the critical point.
d) Note the cycle time 't' (Fig. B4 Mode C) and the
Proportional Band (critical value) setting.
e) Set Proportional Band to:
1.6 times the critical value (for P+D or P+I+D control)
2.2 times the critical value (for P+I control)
2.0 times the critical value (for P only control)
f) Set Integral Time to:
(for P+I+D control)
(for P+D control)
g) Set
Derivative Time to:
(for P+I+D control)
(for P+D control)
The analyzer is now ready for fine tuning by small adjustments to the P, I and D terms, after the introduction
of a small disturbance of the set point.
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