Advanced process control

In control theory Advanced process control (APC) is a broad term composed of different kinds of process control tools, often used for solving multivariable control problems or discrete control problem. Advanced control describes a practice which draws elements from many disciplines ranging from control engineering, signal processing, statistics, decision theory and artificial intelligence

Overview

Advanced process control is composed of different kinds of process control tools, for example:

• Model predictive control (MPC),
• Statistical process control (SPC),
• Run2Run (R2R),
• Fault detection and classification (FDC),
• Sensor control and
• Feedback systems.

APC applications are often used for solving multivariable control or discrete control problems.

Normally an APC system is connected to a distributed control system (DCS). The APC application will calculate moves that are sent to regulatory controllers. Historically the interfaces between DCS and APC systems were dedicated software interfaces. Nowadays the communication protocol between these system is managed via the industry standard OLE for process control (OPC) protocol.

Advanced process control: Topics

APC industries

• APC can be found in the (petro)chemical industries where it makes it possible to control multivariable control problems. Since these controllers contain the dynamic relationships between variables it can predict in the future how variables will behave. Based on these predictions, actions can be taken now to maintain variables within their limits. APC is used when the models can be estimated and do not vary too much.

• In the complex semiconductor industry where several hundred steps with multiple re-entrant possibilities occurs, APC plays an important role for control the overall production.

APC is more and more used in other industries. In the mining industry for example, successful applications of APC (often combine to Fuzzy Logic) have been successfully implemented. In the mining industry, the models change and APC implementation is more complex.

APC Engineers

Those responsible for the design, implementation and maintenance of APC applications are often referred to as APC Engineers or Control Application Engineers. Usually their education is dependent upon the field of specialization. For example, in the chemical industry the vast majority of APC Engineers have a chemical engineering background and typically hold a graduate degree. They combine deep understanding of advanced control techniques with expert process or product knowledge to provide solutions to the most difficult control problems. Because APC engineers are highly specialized many companies elect to contract engineering firms for this type of work. However, some companies view APC as a competitive advantage and maintain a staff of APC engineers who often provide services at more than one geographic location.

Terminology

Manipulated Variables (MVs) are variables where advanced controllers send setpoints to. Controlled variables (CVs) are variables that normally need to be controlled between limits. Disturbance variables (DVs) or Feed Forward variables (FF) are only used as an input to the controller, they cannot be influenced, but when measured contribute to the predictability of the CV.

External links

• Article about Advanced Process Control.
• Press Release. Honeywell Acquires PAS Advanced Process Controls Business
• Case Study. Lancaster Waste Water Treatment Works, optimisation by means of Advanced Process Control from Perceptive Engineering
• APC-network.com Advanced Process Control network for Refining and petrochemical Industry.