Armfield Instruction Manual
106
To begin tuning it is necessary to set initial values which can be modified to improve
the control results obtained. Follow this simple procedure to find start point values
from which to begin optimisation:
Create a new results sheet by selecting the
icon in the tool bar of the software.
Set the set point level to 0mm and allow the process vessel to empty.
Set the software to provide On/Off control (set P to 0%, I to 0s and D to 0s).
Set the set point to 150mm (this allows room for considerable overshoot during the
initial tuning process).
Select the
icon to begin data logging.
Wait as the fluid level rises to the set point and overshoots. Continue logging as the
controller operates the peristaltic pump and the fluid level falls again to below the set
point value. Wait until the fluid level begins to rise once more, then select the
icon to finish data logging.
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 response of the controller. If a slow response is
observed, or large oscillations occur in fluid level after changing the value of P,
reduce the value. 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.
To Next Page
Loading...