Exercise J
97
Increase the outflow rate compared to the inflow rate by fully opening the drain valve.
Log the fluid level as before, and stop logging when the oscillations once more reach
stable values of magnitude and duration.
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 fit the removable
inner cylinder, pressing it down firmly to seal the bottom edge. This reduces 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 Set Point value, feed
rate and inlet/outlet flow rates may be repeated at this reduced 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 J).
Each set of data 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. Compare the
results obtained using time proportioning against those using a simple on/off
controller (as in Exercises H and I).
Discuss the effect of varying the Cycle Time on both the accuracy of control and
wear of the valve being controlled.
Give examples of industrial control situations in which each type of variation in
experimental conditions might occur. For each example, consider the suitability of
time proportional control for that particular application.
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