Armfield Instruction Manual
84
Plot a graph of time against fluid level.
From the graph, determine the peak to peak variation, y, between the highest value
of the overshoot and the lowest value of the undershoot.
Calculate the time between these two values, t.
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, and return the set point level to 0mm to drain the
vessel.
Create a new results sheet by selecting the
icon in the tool bar of the software.
Set the set point to 200mm.
Select the
icon to begin data logging.
Observe the fluid level as it approaches the set point level. Wait until any oscillations
have stabilised, then select the
icon to finish data logging.
From these new results, plot a graph of fluid level 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 fluid level, reduce the value of P. Investigate the results of
the changed value by plotting a graph of the fluid level as it rises from 0mm and
comparing this to the initial results.
Return the value of P to the basic value obtained from the initial measurements.
Integral control can be adjusted to reduce offset in the controlled fluid level. If a
significant offset is observed, reduce the value of I. Investigate the results of any
change by plotting a graph of the fluid level as it rises from 0mm 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
rapid or large, reduce the value of D. Investigate the results of the changed value by
plotting a graph of the fluid level as it rises from 0mm and comparing this to the initial
results.
Leaving the optimised value of D, set the values of P and I to the optimised values
found by experiment. Perform a final test run, logging the fluid level over time as it
rises from 0mm. Compare this to the initial graph.
Feed Rate
Create a new results sheet by selecting the icon in the tool bar of the software.
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