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Exercise E - Proportional pressure input with time
proportional control using Normally Closed solenoid
valve
Objective
To control the level in the process vessel using a time-proportional controller
connected to a pressure sensor, with a Normally Closed solenoid valve (SOL1)
controlling inflow to the vessel.
Overview
The control system in this exercise consists of a pressure sensor with an output
proportional to the pressure exerted on the sensor. The output is sent to a time
proportional controller which operates an on/off flow switch. The time proportioning
controller turns the output on and off at intervals. This ratio of time “on” to time “off”
may be set manually, or may be set automatically by the controller which then varies
the ratio according to the difference between the current control variable and the
required Set Point value.
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 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. The apparatus should not be left unattended
once in operation, and manual operation of the inlet pressure regulator and drain
valve should be used to control the fluid level if the vessel volume reaches the
overflow pipe, or the drainage channel in the plinth becomes full of water.
Run the PCT40 software and select Section 1: Level Control (inflow). Select the
icon to view the mimic diagram screen. Check that ‘On/Off – Solenoid 1’ is set to
‘Controller’.
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