Armfield Instruction Manual
180
From the values y and t, starting values may be found for P, I and D as follows
P = y / 3
I = t
D = t / 6
Set these values in the software.
Create a new results sheet by selecting the
icon in the tool bar of the software.
Select the
icon to begin data logging.
Log the flow rate as it rises and then settles around the set point value. Logging
should continue until any oscillations have settled.
Select the
icon to finish data logging.
From these new results, plot a graph of flow rate against time and observe the shape
of the graph.
Proportional control sets the gain of the controller. If a slow response is observed, or
large oscillations occur in flow, reduce the value of P. Investigate the results of the
changed value by plotting a graph of the flow as it rises from a low value and
comparing this to the initial results.
Integral control can be adjusted to reduce offset in the flow rate. If a significant offset
is observed, reduce the value of I. Investigate the results of any change by plotting a
graph of the flow rate as it rises from a low value and comparing this to the initial
results.
Return the value of I to the basic value obtained from the initial measurements.
Derivative control can be adjusted to reduce excessive oscillation. If oscillations are
extreme, reduce the value of D. Investigate the results of the changed value by
plotting a graph of the flow rate as it rises from a low value and comparing this to the
initial results.
From the graphs obtained, select values of P, I and D that give the best results.
Perform a final test run, logging the flow rate over time as it rises from a low value.
Compare this to the initial graph.
Results
For easy identification or results, it is suggested that each results sheet is renamed
with a descriptive title (e.g. ‘Flow Rate’, ‘Integral Setting’, etc.). The entire workbook
should be saved with a suitable filename for future reference (e.g. PCT40 Exercise
CC).
Each set of data not already graphed as part of the procedure should be plotted on a
graph of flow rate F1 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
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