89
Exercise I - Proportional pressure input with on/off
controller using Normally Closed solenoid valve
Objective
To control the level in a process vessel using an on/off controller connected to a
pressure sensor, with a Normally Closed solenoid valve (SOL2) controlling outflow
from the vessel.
Overview
The proportional pressure control method in this exercise consists of a pressure
sensor with an output proportional to the pressure exerted on the sensor. The output
is sent to an on/off controller that controls a Normally Closed solenoid valve.
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 Installation section.
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 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 SOL1 at the front right of
the plinth.
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
Switch on mains power to the console and run the PCT40 software. Select ‘Section
3: Level Control (outflow)’.
In the PCT40 software, set the PSV to operate at 75%. Refer to the flow meter
display and adjust the PSV setting to give a flow rate of 1 L/min using the arrow keys.
Select ‘Configure’ from the Sample menu, and set sampling to Automatic at intervals
of 10 seconds, with duration as Continuous.
Setting the On/Off Controller
In the PCT40 software, select ‘Control’ to open the PID controller window.
Set the Proportional Band (P) to 0%, the Integral Time (I) to 0s and the Derivative
Time (D) to 0s. The controller is now set as a simple On/Off controller with fixed
hysteresis of 0.5% of full scale.
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