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Exercise CC - Proportional flow rate input with PID control
Objective
To control the flow rate of water using PID control of a peristaltic pump, using a flow
sensor to monitor the rate.
Overview
Flow is directed through a flow sensor by a peristaltic pump. The flow sensor sends a
signal to the computer that is proportional to the flow rate. The PID controller within
the software monitors this signal and adjusts the speed of the pump to reach and
maintain the required flow rate.
Equipment Required
PCT40 bench.
Equipment set up
Ensure that the apparatus has been set up according to the Installation section.
Check that the mains water supply to the apparatus is off and the pressure regulator
is set to minimum. The apparatus should be connected to a suitable PC with the
PCT40 software installed, using the grey USB cable provided.
Take a length of 6.3mm diameter peristaltic tubing with a self-sealing fitting at one
end. Connect the quick-release fitting to the socket on SOL 1. Pass the other end
from right to left through the left-hand peristaltic pump (pump A) to a suitable drain.
Leave the lid of the pump open at this stage.
Take a second length of tube with a grey Guest push fitting at one end. Remove the
quick-release sealing plug from the end of the inlet plumbing (in front of SOL 1).
Connect the tubing to the pipe where the plug was located. Pass the other end from
right to left through the right-hand peristaltic pump (pump B) to a suitable drain.
Leave the lid of the pump open at this stage.
Check that the drain valve on the end of the plinth is open and that it is connected to
a suitable drain.
Procedure
NOTE: Peristaltic pumps typically do not begin to operate until the input reaches
approximately 30%. During PID control, if the Proportional Band is loo large then the
controller will not send a great enough input value to begin pump operation. If the
pump fails to operate under PID control, try reducing the PB value.
Switch on the mains water supply to the apparatus.
Run the PCT40 software and select ‘Section 9: Flow Control’.
Select ‘Configure...’ from the Sample menu. Set data logging to Automatic at 5
second intervals with Continuous duration.
Prime the pumps:
In the software, open valve SOL 1
Set the speed of pump B to 50%
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