Exercise G
85
Select the
icon to begin data logging.
To change the inlet feed rate, adjust the pressure regulator on the inlet pipe of the
apparatus: Pull the knob outwards from the body of the regulator, turn the knob a
half-turn anticlockwise then lock the value by pushing the knob back in.
Note the action of the PSV.
Wait until the oscillations in fluid level stabilise in magnitude and duration, then select
the
icon to finish data logging.
Repeat the feed rate exercise by reducing the inlet flow rate in steps until the fluid
level in the vessel no longer returns to the Set Point level (the drain rate exceeds the
inlet flow rate). For each step create a new results sheet before starting data logging,
and continue logging until the oscillations stabilise.
Effect of Vessel Volume
In the software, close the valve SOL1. This will stop flow into the large process
vessel.
Fully open the drain valve in the base of the large process vessel and allow the water
to drain from the vessel.
Carefully remove the lid on top of the large process vessel and remove the inner
cylinder. This increases the effective volume of the process vessel.
Replace the lid and partially close the drain valve.
Repeat the procedure described at the start of the exercise, remembering to create a
new results sheet before commencing data logging.
If there is sufficient laboratory time then the investigations of disturbances, Set Point
value, PID settings and feed rate may be repeated at this increased volume.
Results
For easy identification or results, it is suggested that each results sheet is renamed
with a descriptive title (e.g. ‘Flowrate’, ‘Volume’, etc.). The entire workbook should be
saved with a suitable filename for future reference (e.g. PCT40 Exercise G).
Each set of data not already graphed as part of the procedure should be plotted on a
graph of fluid level against time.
Make a comparison of each variation in the experimental conditions against the
graph of the initial set of results, noting the difference in response. Comment on the
results obtained by varying the values of P, I and D, and on the ease of optimisation
of the process. Compare the results obtained using PID control against those using a
simple on/off controller (as in Exercises A and C) and time proportioning control
(Exercise F).
Give examples of industrial control situations in which each type of variation in
experimental conditions might occur. For each example, consider the suitability of
PID control for that particular application.
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