Exercise CC
179
Change the speed of pump B to 0%. Wait until the flow rate settles to a steady value,
and then select the
icon to finish data logging.
Flow Rate 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 flow rate set point to 1000ml/min.
Select the
icon to begin data logging.
Log the flow rate 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 flow rate
over time. Suggested values for the flow rate set point are 500ml/min and 300ml/min,
but more values may be attempted if laboratory time allows. Remember to create a
new results sheet for each set of data.
Return the flow rate 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.
Set the software to provide On/Off control (set P to 0%).
Set the flow rate set point to 1000ml/min (this allows for overshoot during the initial
tuning process).
Select the
icon to begin data logging.
Wait as the flow rate rises to the set point and overshoots. Continue logging as the
controller starts the peristaltic pump, introducing flow through the second pump and
therefore reducing flow through the first pump as the pressure regulator maintains
constant water pressure. Continue logging until the controller switches off the pump
and the flow rate begins to rise once more, then select the
icon to finish data
logging.
Plot a graph of flow rate against time.
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.
To Next Page
Loading...