This exercise is to control the fluid level in a tank to ensure
sufficient supply to downstream facilities. It will be necessary to generate and control a
series of alarms if the fluid level is too low or, on the contrary, when an overflow is about
to occur. The top section of the window shows the tank with four level sensors which
check normal operation and fluid low/high level limits. Each sensor is energised whenever
the fluid level in the tank exceeds its position. When one sensor is
energised, the
corresponding LED is lit.
The feed and the supply tubing are valve controlled. Selector switches allow
various operating modes to be enabled: manual valve open; manual valve closed and automatic.
When in automatic mode, the position of the inlet tap valve is defined from the PLC output
to which it is connected. The position of the outlet tap valve is randomly defined, in
order to simulate the different fluid demand from downstream facilities.
The bottom section of the window contains a control and alarm panel; two warning light
indicators and a siren are available along with alarm reset and siren off buttons.
The Trend recorder window simulates an instrument that is common in industrial
applications: a chart recorder. On graph paper, organised with percentage (vertical)
versus time scale (horizontal), a dot representing the tank level is continuously plotted
in real time. A level trend signal is then graphically displayed to allow
evaluation off the effectiveness of any adjustments made.
When the available screen space is full, the window scrolls: last samples disappear
and space is provided for new samples.
