APCS - standard structure

Standard structure

In production an APCS of a system usually are based on the three-level principle.

• The bottom level (field level, field) an APCS represents different sensors (sensors) and actuators.
• The average level (level of controllers) consists of programmable logic controllers (a PLC, in English-speaking literature - PLC). It just accepts field data and issues control instructions on the bottom level. Control in a PLC is exercised on in advance developed algorithm which is performed cyclically (data reception – processing – issue of managing commands).
• The top level is the level of visualization, scheduling (monitoring) and data collection. At this level the person, i.e. the operator (manager) is involved. If it exercises control of the local unit (machine), then for its implementation the so-called human-computer interface is used (HMI, Human-Machine Interface). If the operator exercises control of distributed system of machines, mechanisms and units, then we will often apply the term SCADA to such dispatching systems (Supervisory Control And Data Acqusition is supervisory control and data collection, English). In both cases the top level of an APCS provides collecting and also archiving of the major data from a PLC, their visualization, i.e. visual (in the form of the symbolic circuits which are often animated) representation on the screen a being and parameters of the happening process. At data acquisition a system independently compares them to boundary parameters (settings) and at an exit for borders notifies the operator using alarms. The operator who to start work should become authorized (to be registered) starts technology process, has an opportunity to stop it in whole or in part, can change operation modes of units (changing settings), etc. At the same time a system writes all events, including actions of the operator, providing "blamestorming session" in case of accident or other emergency situation. Thereby the personal responsibility of the managing operator is provided.

Those subsystems of an APCS which are critical by the time of a response to different events of process have the name of real-time control system (RV). For them delay in issue of the control message as it is fraught with accident is inadmissible. In most cases PLCs are created as the RV system, for them time of a cycle of work of a managing algorithm also is the maximum response time of the RV system.

The APCS major element are networks on which data and control instructions are transferred. Often lower and average APCS levels integrate "the field bus" which is network with the guaranteed delivery time of packets that allows to create the distributed control system (RSU – DCS=Distributed Control System) working in the RV mode. The application at the top level of an APCS is usually not demanded by works in the RV mode therefore computers are connected here are connected among themselves by an Ethernet network that allows an APCS to integrate easily with management systems of the ACS level of the enterprise, sending production data to databases of the enterprise.

In the general context, the PCS is a concept of creation of local, guaranteed reliable solutions of direct manipulation by the equipment as components of the uniform effective instrument of operational production management.

By information technologies, the PCS - a set of the software and hardware complexes implementing one of the main objectives of the enterprise - production. Each separate complex manages the corresponding technology process, and in total they cover all production in general.

See Also

SCADA