The responsible technician can take control over the automatic controller in
order to operate the input and output pumps directly. For this purpose, each
PLC has a graphical console that displays the current status of each pump
and allows the technician to modify the paint flow.
The supervisory console is a graphical interface that displays the tonality of
paint in the mixture tank. The responsible technician can select a new
colour by varying the percentage of the three fundamental colours. For the
sake of simplicity, we use the RGB palette although this is not appropriate to
represent the behaviour of real paints. Using the RGB palette, a generic
colour is obtained as the sum of light emissions of the three RGB compo-
nents. The RGB palette is meant for display on monitors. A generic colour of
real paint is obtained as the sum of light absorption of three fundamental
paint colours (i.e. magenta, cyan, yellow). Once the new colour has been
mixed in the mixture tank, the technician can open the spray pump. The
supervisory console regulates the output flow.
The painting work cell is simulated by a software application that has a
graphical interface depicting the system as in Figure 13.1 and showing its
The SCADA system is physically distributed over a wide area. The colour
tanks and the mixture tank may be quite far from each other; the super-
visory station may be outside the work cell. The design of the SCADA system
should favour a seamless transition from the simulated work cell to the
interconnection with the real system.
The SCADA system is a distributed system made up of six main components:
the plant simulator, the four PLCs and the supervisory console.
The first requirement of the system components is to manage independent
The simulator manages a graphical interface that displays the paint levels
within the tanks and the paint flows of the input and output pumps. It ani-
mates the car painting process by updating the current status of tanks and
pumps continuously. It interacts with the controllers in order to receive
commands and give feedback.
The PLCs implement the control logic that keeps the physical equipment
in a coherent state. They interact with the simulator and the supervisory