Armfield Instruction Manual
142
section. This may be speeded up by increasing the flow rate through the vessel. Fully
open the drain valve in the base of the vessel, and increase the PSV setting to
maintain the fluid level. Close the drain and return the PSV to its previous setting
after cooling the water to 30°C or less.
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. This process will take some time, as the
water cools slowly.
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 temporarily increase the flow rate through the
vessel to accelerate the cooling process. Return the flow rate to its previous value
before continuing with the exercise.
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- 10 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.
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