Armfield Instruction Manual
76
Log the fluid level as before, adjusting the percentage until a stable level is
maintained. Log for a further minute at constant fluid level, then select the
icon to
finish data logging.
Effect of Vessel Volume
Open the PID controller window. Set the Mode of Operation to ‘Manual’ and set
‘Manual Output’ to 0%. This will close the valve SOL 1 and 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 Set Point value, feed
rate and inlet/outlet flow rates 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 E).
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 A and C).
Give examples of industrial control situations in which each type of variation in
experimental conditions might occur. For each example, consider the suitability of the
switch used for that particular application.
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