Exercise L
103
Run the PCT40 software. Select ‘Section 4: Level Control (outflow)’.
In the software, open the PSV by selecting a setting of 100%. Observe that water
begins to flow into the process vessel.
In the software, set the fluid Set Point level to 0mm, wait until the peristaltic pump
begins to operate, then close the lid on the pump. Take care that the tubing through
the pump passes through the inlet and outlet holes and is not pinched by the lid of
the pump.
Partially close the drain valve on the bottom of the large process vessel to slightly
reduce the outlet flow rate.
Select ‘Configure’ from the Sample menu, and set sampling to Automatic at intervals
of 10 seconds, with duration as Continuous.
In the software, click on the PID controller button and set the value of the fluid Set
Point to the desired height. A value of 200mm is suggested.
Set the PID values for the controller in the appropriate boxes in the software.
Suggested starting values are Proportional Band (P) of 5%, Integral Time Constant
(I) of 0s and Differential Time Constant (D) of 0s.
Select the
icon to begin data logging as the process vessel continues to fill with
water.
Observe the fluid level in the vessel and the action of the peristaltic pump as the level
approaches the Set Point value. The fluid level will oscillate about the Set Point
value. Continue logging until the oscillations reach stable values, then select the
icon to finish data logging.
Disturbances
Within the software it is possible to introduce disturbances in the outflow from the
vessel by operating the Normally Closed solenoid valves SOL 2 and SOL 3:
Create a new results sheet by selecting the
icon in the tool bar of the software.
Select the
icon to begin data logging.
In the software, select the switch to open valve SOL 2. Observe the variation in the
peristaltic speed setting displayed in the software, and the oscillations in fluid level in
the process vessel.
Wait until the oscillations in fluid level stabilise in magnitude and duration, then select
the
icon to finish data logging.
Create a new results sheet by selecting the
icon in the tool bar of the software.
Close valve SOL 2 and open valve SOL 3.
Select the
icon to begin data logging.
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