Exercise 6: Controller Tuning

Question 1

Below are a range of responses of several process measurements to a step change in an adjustment of 50% of its maximum range.

If each of the measurements represents an alternative control loop pairing with the adjustment, rank these in order of desirability with a brief explanantion of your choice.

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Question 2

A control room chart record, see the figures below, shows a test on a process in which a control valve was opened from 10% to 50% of its range and the effect on the measurement, to be used in a control loop with the valve, recorded. The top and bottom of the chart represent upper and lower range limits on the measurement.

Recommend settings (proportional band and reset time) for

Proportional Controller
Proportional Integral Controller

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Question 3

The temperature of a chemical reactor is to be regulated by adjusting the flow of heating fluid to a jacket.

The following data is available:

Heating fluid maximum flowrate = 10kg/s
Temperature measurement
- Minimum reading = 20^oC
- Maximum reading = 220^oC

The heating fluid valve is initially 20% open and the measured temperature is 140^oC. The valve is then opened to 40% and the temperature finally settles down at 173^oC.

If the relationship between heating fluid flow and reactor temperature is assumed to be linear what is the relationship?
What is the value of the dimensional process gain and what are its dimensions?
What is the dimensionless process gain?
If the reactor temperature is to be controlled at 180^oC using a proportional-only controller, what percentage manual offset would you recommend?
Experimental tuning of the process suggests the use of a dimensionless controller gain, standardised to a unity gain process, of 2.4. To what proportional band setting does this correspond?
A theoretical investigation of the process suggests a dimensional controller gain of 0.2kg/s/^oC. What proportional band does this represent?

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