Answer to question 7.15
Control performance criteria are presented in Chapter 7. Here, some of the criteria are given in the following table with the results for the two cases. The preferred response is noted in green.
| Performance Criteria | Case A | Case B |
| Stable | Yes | Yes |
| Returns controlled variable to its set point (zero offset) | Yes | Yes |
| IAE (integral abs. value of error) | 24.9 (smaller) | 33.0 |
| Rise time | 25 | 17 (faster) |
| Settling time | 25 (smaller) | 100+ |
| Decay ratio | 0 (smaller) | 2/7 (too large) |
| Max. CV deviation from set point | Not applicable to set point changes responses. This metric is relevant for disturbance responses! | |
| MV overshoot from its final value | 10/25 (smaller) | 20/25 |
In general, CASE A provides better performance and would be preferred in most industrial applications. It provides better performance in all items except rise time, and the fast rise time in Case B is achieved by feedback that is too aggressive.