Exercise EE
187
Disturbances
Within the software, it is possible to introduce a disturbance to the flow rate, and
therefore the differential pressure, by altering the speed of the gear pump:
In the software, select the
icon to create a new results sheet.
Select the
icon to begin data logging.
In the software, change the speed of the gear pump to 70%.
Log the pressure P3 as the PID controller adjusts to the changed flow rate through
the orifice. Wait until the flow rate settles to a steady value.
Change the speed of pump B to 30%. Wait until the pressure P3 settles to a steady
value.
Change the speed of pump B to 50%. Wait until the pressure P3 settles to a steady
value, and then select the icon to finish data logging.
Differential Pressure Set Point
Investigate the effect of changing the set point flow rate:
Create a new results sheet by selecting the
icon.
In the software, alter the set point to 150mm.
Select the
icon to begin data logging.
Log the pressure P3 until it settles at the new set point, and then select the
icon
to finish data logging.
Repeat the procedure, altering the set point and recording the change in pressure
over time. Suggested values for the set point are 100mm, 250mm and 300mm, but
more values may be attempted if laboratory time allows. Remember to create a new
results sheet for each set of data.
Return the set point to its original value.
PID Settings and optimisation
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.
In the PID control window, set the software to provide On/Off control (set P to 0%).
Set the pressure set point to 150mm (this allows for overshoot during the initial tuning
process).
Select Manual Control and set the PSV to 0%.
Select the
icon to begin data logging.
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