Armfield PCT40 - Exercise B - Differential Level Switch

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Exercise B - Differential level switch
Objective
To control the level in the process vessel using a differential level switch with a
Normally Closed solenoid valve (SOL1) controlling inflow to the vessel.
Overview
The differential level switch used in this exercise consists of a pair of electrodes and
a fixed earth rod (a metal ruler). The switch works by measuring the conductance
between the electrodes and the earth rod. The conductance through air is different to
that through water, and hence the conductance measured differs if one or both
electrodes are touching the water. This can be used to create a switch that is
triggered by the water level within the process vessel, with the electrodes adjusted to
different heights to give a maximum and minimum level.
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.
Check that the differential level switch is connected correctly to the plinth. The lead
ending in three banana plugs should be connected at the opposite end to the back of
the plinth. The three banana plugs should be connected as follows:
The green plug (green and yellow wire) to the socket on the back of the differential
level switch (the connection behind the metal ruler).
The blue plug (blue wire) to the top of the left-hand rod on the differential level switch,
which should be positioned to give the low level setpoint.
The red plug (brown wire) to the top of the right-hand rod on the differential level
switch, which should be positioned to give the high level setpoint.
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.