102
Exercise L - Proportional pressure input with PID
controller to control peristaltic outlet pump speed
Objective
To control the level in the process vessel with a PID controller, using a pressure
sensor to monitor the level with a peristaltic pump controlling outflow to the vessel.
Overview
The proportional pressure sensor sends a signal to the controller that varies with the
pressure on the sensor resulting from the depth of fluid. The controller sends a signal
to the peristaltic pump that is proportional to the signal from the sensor. The pump
speed increases or decreases proportionally with the signal from the controller.
Equipment Required
PCT40 bench with large process vessel, inner cylinder and supplied flexible tubing.
Equipment set up
Ensure that the apparatus has been set up according to the assembly sheet (see
also Appendix A in this manual). Ensure that the inlet connector for the apparatus (on
the right of the plinth behind the pressure regulator) is connected to a suitable mains
water supply. Check that the central cylinder is securely in position inside the large
process vessel.
Using a suitable length of tubing, connect the self-sealing connection socket on the
base of the large process vessel to the quick release connection on the valve PSV1
at the front right of the plinth. Take a length of 4.8mm diameter peristaltic tubing with
one self-sealing end and one open end, and connect the self-sealing fitting to the
drain tube inserted through the lid of the large process vessel. Pass the peristaltic
tube from right to left through the peristaltic pump A, but do not yet close the pump.
Direct the open end to a suitable drain.
The drain valve at the end of the plinth should be directed to a drain and left open.
Solenoid valves 2 and 3 should be connected to a suitable drain using the tubing
supplied. The drain valve in the base of the large process vessel should also be
connected directly to drain using flexible tubing.
Connect the apparatus to a suitable PC on which the software has been installed
using the pale grey USB cable supplied. The flat connector on the cable connects to
the PC, usually via a socket at the back. The other end connects to the socket on the
orange panel on the front of the plinth. Check that the PC is working and switched
on.
Procedure
NOTE: Peristaltic pumps typically do not begin to operate until the input signal
reaches approximately 30%. When controlling a peristaltic pump with a PID
controller, the pump will therefore not begin to operate if the Proportional Band is too
large (as the controller will not send a large enough signal to start the pump). If the
pump fails to operate after changing the Proportional Band, try decreasing the value
of PB.
Switch on mains power to the console. Valve PSV is Normally Closed, so flow into
the large process vessel will not occur until the valve is in operation.
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