Approximately around to the end of the years 70' the companies that produced electronic and electrical systems for the industry they have begun to address their laboratories of search, in the development and use of the systems micro processore in order to realize automations and controls of process, before put into effect through systems of wired logic.

Wired logic had large uses in the industry, but it had also great disadvantages:

• Great complexity and mass of the switchboards with exponential cabling respect the processes served.
• Not time critical communication
• Diminish of plant reliability to the great number of device and rel柩n use that statistically increase the possibilities of breakdowns.
• In case of breakdowns and malfunction the search of the cause and the resolution could demand much time.
  With consequent long downs of production.
• In order to modify the process or to widen it, many days of study, and remarkable modifications to the system were necessary.
  With consequent long downs of production.

Therefore this new product based on microprocessore that could be only for all the applications, and customizable for every system to second of the requirements of the customer, would have constituted an other small industrial revolution.

The development of this technology for various demands for the market, uniforms in two macro categories:

• DCS (Distributed Control System)

  

• PLC (Programmable Logical Controller)

  

The DCS were conceived in order to elaborate great amounts of data and complex mathematical developments, with the possibility to be connect between they in net. They answered to the requirements of the chemical, druggist, petrochemical industry that had need to elaborate marks them analogic for the control of process (much expensive)

The PLC were conceived in order to elaborate small amounts of data mostly of digital type, with the clear scope to replace wired logic. They answered to the requirements of the constructors of switchboards for the control of blot some, and replaced rel檠impulse-counter, timers (little expensive)

As it is easy to comprise the spread of the PLC has been enormous thanks also to the wide park customers to which it addressed. This enormous spread and the continuous industrial innovation has allowed to the PLC one remarkable technological development, equipping it in modular way of more and more complex functions that have approached to the greater brother DCS il also evolved in way more and more aimed at the fields of its competence.

With the spread of the PC in the years 80' the situation of the process control has assumed one new compages, in fact the development of interfaces between PC and Plc-Dcs has given the possibility to create one historical data before not present (in the PLC), and one graphical view of the process and of its acquired data more evolved and easy to use.

In the years 90' both legacies to the PC are born two new elements in the world of the control of process:

• SCADA (Supervision, Control and Data Acquisition)

  

• Soft PLC (PLC based on system PC)

  

The software packages SCADA has had a fast development, and are becomes an integrating part of one modern supply of automation, with to the DSC or the PLC.

Soft PLC instead finds hard spread, contrasted from the great confidence earned on the field from the PLC and, from other from the distrust on the PC operating systems on performance 24/7.