Armfield Instruction Manual
122
Create a new results sheet by selecting the
icon in the tool bar of the software.
Set the software to provide On/Off control (set P to 0%).
Set the temperature set point to 40°C (this allows room for overshoot during the initial
tuning process).
Select the
icon to begin data logging.
Wait as the temperature rises to the set point and overshoots. Continue logging as
the controller switches off the heater and the water cools. Continue logging until the
controller switches on the heater and the temperature begins to rise once more, then
select the
icon to finish data logging. The cooling process will take some time, as
the water cools slowly. DO NOT increase the cooling rate by passing cold water
through the coil.
Plot a graph of time against water temperature.
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.
Change the temperature set point to 0°C, and cool the water in the vessel to 30°C or
less. At this point it is possible to use cold water in the heating coil to accelerate the
cooling process.
Create a new results sheet by selecting the
icon in the tool bar of the software.
Return the temperature set point to 40°C
Select the
icon to begin data logging.
Log the temperature as it rises and then settles around the set point value. Logging
should continue until any oscillations have settled- 15 minutes is suggested.
Select the
icon to finish data logging.
From these new results, plot a graph of temperature T1 against time and observe the
shape of the graph.
If the figure for Proportional Band obtained by this method is very small (less than
5%), and the Integral Time very large (more than 30s) then the method chosen for
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