Notes on Controller Parameters Correlations
The purpose of tuning correlations is to enable the engineer to
calculate tuning constants for many process applications without having
to perform the optimization. Values for the controller parameters are
given as dimensionless numbers which can be adapted depending on the
process.
The method is outlined below:
- Look at the open loop response of the process to a step change in
the manipulated variable.
- Evaluate
- The steady-state gain, (y2 - y1) / (u2 - u1)
- The time delay, Td
- The time constant, Ts
- Hence evaluate the fractional dead time - Tf = Td / (Td + Ts)
- Now look at the table below and determine the dimensionless gain and
reset time for the correlation of your choice:
|
Ciancone |
Lopez |
ZN (open) |
| Tf |
 |
 |
|
|
|
|
| 0 |
1.1 |
0.23 |
5.8 |
0.4 |
- |
- |
| 0.1 |
1.1 |
0.23 |
5.8 |
0.5 |
8.1 |
0.33 |
| 0.2 |
1.8 |
0.23 |
3.1 |
0.6 |
3.6 |
0.66 |
| 0.3 |
1.1 |
0.72 |
2.1 |
0.7 |
2.1 |
1.0 |
| 0.4 |
1.0 |
0.72 |
1.7 |
0.8 |
1.35 |
1.32 |
| 0.5 |
0.8 |
0.70 |
0.91 |
0.9 |
0.9 |
1.65 |
| 0.6 |
0.59 |
0.67 |
- |
- |
0.67 |
1.98 |
| 0.7 |
0.42 |
0.60 |
- |
- |
0.43 |
2.31 |
| 0.8 |
0.32 |
0.53 |
- |
- |
0.25 |
2.64 |
- Once you have the values for the dimensionless groups it is possible
to evaluate the actual values of the controller gain and controller reset
time.
- = controller gain * process gain
- = controller reset time / (Td + Ts)
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