Programmable automation controller
Encyclopedia
A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system
with that of a typical programmable logic controller
(PLC). PACs are most often used in industrial settings for process control
, data acquisition
, remote equipment monitoring, machine vision
, and motion control
. Additionally, because they function and communicate over popular network interface
protocols
like TCP/IP, OLE for process control
(OPC) and SMTP, PACs are able to transfer data from the machines they control to other machines and components in a networked control system or to application software
and databases.
, process control, and data acquisition functions such as digital
and analog
control, serial string handling, PID
, motion control, and machine vision. The parameters within which PACs operate to achieve this, however, sometimes run counter to how a PLC functions.
Unlike PLCs, PACs offer open, modular architectures, the rationale being that because most industrial applications are customized, the control hardware used for them needs to allow engineers to pick and choose the other components in the control system architecture without having to worry whether or not they will be compatible with the controller.
PACs and PLCs are also programmed differently. PLCs are often programmed in ladder logic
, a graphical programming language resembling the rails and rungs of ladders that is designed to emulate old electrical relay
wiring diagrams. PAC control programs are usually developed with more generic software tools that permit the designed program to be shared across several different machines, processors, HMI terminals or other components in the control system architecture.
PAC processing and I/O
scanning is also very different. Unlike PLCs, which constantly scan all the I/O inputs in the control system at very high speeds, PACs utilize a single tagname database and a logical address
system to identify and map I/O points as needed.
Well known control hardware vendors offering PACs include Advantech Corporation,Invensys
Foxboro, Schneider Electric
, General Electric
, National Instruments
, Opto 22
, and Allen Bradley.
Control system
A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...
with that of a typical programmable logic controller
Programmable logic controller
A programmable logic controller or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines...
(PLC). PACs are most often used in industrial settings for process control
Process control
Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range...
, data acquisition
Data acquisition
Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems typically convert analog waveforms into digital values for processing...
, remote equipment monitoring, machine vision
Machine vision
Machine vision is the process of applying a range of technologies and methods to provide imaging-based automatic inspection, process control and robot guidance in industrial applications. While the scope of MV is broad and a comprehensive definition is difficult to distil, a "generally accepted...
, and motion control
Motion control
Motion control is a sub-field of automation, in which the position or velocity of machines are controlled using some type of device such as a hydraulic pump, linear actuator, or an electric motor, generally a servo...
. Additionally, because they function and communicate over popular network interface
Network interface
Network interface may refer to:* Network interface controller, the device a computer uses to connect to a computer network* Network interface device, a demarcation point for a telephone network...
protocols
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
like TCP/IP, OLE for process control
OLE for process control
OLE for Process Control , which stands for Object Linking and Embedding for Process Control, is the original name for a standards specification developed in 1996 by an industrial automation industry task force...
(OPC) and SMTP, PACs are able to transfer data from the machines they control to other machines and components in a networked control system or to application software
Application software
Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
and databases.
PAC Origins
The ARC Advisory Group, an analyst group focused on the manufacturing industry, is generally credited for originating the term "PAC". It was first coined in 2001 as a way to help users of control hardware better define their needs, and to give the leading control hardware vendors a term to more clearly communicate the capabilities of their products.PAC - PLC Comparison
Generally, PACs and PLCs serve the same purpose. Both are primarily used to perform automationAutomation
Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...
, process control, and data acquisition functions such as digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
and analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
control, serial string handling, PID
PID
-Medicine:*Prolapsed intervertebral disc, commonly called a "herniated disc"*Primary immune deficiency, disorders in which part of the body's immune system is missing or does not function properly...
, motion control, and machine vision. The parameters within which PACs operate to achieve this, however, sometimes run counter to how a PLC functions.
Unlike PLCs, PACs offer open, modular architectures, the rationale being that because most industrial applications are customized, the control hardware used for them needs to allow engineers to pick and choose the other components in the control system architecture without having to worry whether or not they will be compatible with the controller.
PACs and PLCs are also programmed differently. PLCs are often programmed in ladder logic
Ladder logic
Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay logic hardware. It is primarily used to develop software for programmable logic controllers used in industrial control applications...
, a graphical programming language resembling the rails and rungs of ladders that is designed to emulate old electrical relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
wiring diagrams. PAC control programs are usually developed with more generic software tools that permit the designed program to be shared across several different machines, processors, HMI terminals or other components in the control system architecture.
PAC processing and I/O
I/O
I/O may refer to:* Input/output, a system of communication for information processing systems* Input-output model, an economic model of flow prediction between sectors...
scanning is also very different. Unlike PLCs, which constantly scan all the I/O inputs in the control system at very high speeds, PACs utilize a single tagname database and a logical address
Logical address
In computing, a logical address is the address at which an item appears to reside from the perspective of an executing application program....
system to identify and map I/O points as needed.
Well known control hardware vendors offering PACs include Advantech Corporation,Invensys
Invensys
Invensys plc is a global engineering and information technology company headquartered in London, United Kingdom. It was formed in 1999 through the merger of BTR plc and Siebe plc. It has offices in more than 50 countries and its products are sold in around 180 countries.Invensys is organised into...
Foxboro, Schneider Electric
Schneider Electric
Schneider Electric is a French global company. It was founded in 1836 by two brothers, Eugène and Adolphe Schneider.In the first part of the 20th century, Schneider et Cie associated itself with Westinghouse Systems, a major international electrical group at the time. The group began manufacturing...
, General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
, National Instruments
National Instruments
National Instruments Corporation, or NI , is an American company with over 5,000 employees and direct operations in 41 countries. Headquartered in Austin, Texas, it is a producer of automated test equipment and virtual instrumentation software...
, Opto 22
Opto 22
Opto 22 is a manufacturing company specializing in hardware and software products for industrial automation, remote monitoring, and data acquisition. The company is based in Southern California and is well-known in the automation and control industry for its history of innovation in the development...
, and Allen Bradley.