Figure 13.13 The graphical interfaces of the entire SCADA system. Copyright © 2005
Sun Microsystems, Inc. All rights reserved. Reproduced by permission of Sun Microsystems, Inc.
getting empty, the colour tanks should supply paint flows according to the
The reader can extend the SCADA system in several ways:
The main limitation of the third prototype is the waste of paint when the
technician changes the colour tonality. In fact the mixture needs to be
emptied before the new paint flows start filling the tank. A better solution
would be to mix the current paint in the tank with new paint flows from
the fundamental colour tanks. This would require the evaluation of the
exact quantity of paint already present in the tank for each fundamental
colour and the quantity of colour to be added to get the desired tonality.
In some cases, this approach may still require draining a certain amount
of paint from the mixture tank.
The synchronization between the PLCs and the simulator is handled with
the polling mechanism. Think about the possibility of using the event
notification mechanism. This is critical if we want the PLCs to be able to
deal with exceptional conditions. For example, it might happen that the
input pumps of the tank controllers are disabled because there is no more
paint supply from outside the work cell.
Real SCADA systems are structured around a central database. Its intro-
duction may require the redefinition of the system architecture in terms
of interconnection between the distributed components.