Programmable Automation Controller (PAC):
Programmable automation controller (PAC) systems consist of PAC modules, each of which performs a specific function. PAC systems are used in motion control, machine control, machine vision, and other industrial control applications. They include the following types of PAC modules: analog I/O modules, digital I/O modules, relay modules, counter modules, serial modules, servo or stepper controller modules, timer modules, and data acquisition modules. PAC systems with analog I/O modules are used to measure and control industrial automation devices such sensors and actuators. They can also be used to condition high or low voltage signals, thermocouples, resistance temperature detectors (RTD) and strain gauges. PAC systems with digital I/O modules are used to measure and control industrial automation devices such sensors and actuators. PAC systems with data acquisition modules digitize and process multiple sensor or signal inputs for monitoring, analyzing and/or controlling systems and processes. PAC systems with serial modules coordinate the flow of data, control signals, and timing information between data terminal equipment (DTE) and data communication equipment (DCE).
Programmable automation controller (PAC) systems have backplane slots for adding input/output (I/O) modules and differ by backplane bus type. The VersaModule Eurocard bus (VMEbus) is a popular, 32-bit bus used in industrial, commercial and military applications. VME extensions for instrumentation (VXI) is an electrical and mechanical standard used with automatic test equipment (ATE). Peripheral component interconnect (PCI) is a local bus system designed for high-end computer systems. Compact PCI (cPCI) uses the electrical standards of the PCI bus, but is packaged in a Eurocard. PCI extensions for instrumentation (PXI) is a superset of CompactPCI that adds timing and triggering functions. In terms of ports and interfaces, some programmable automation controller (PAC) systems have an Ethernet, universal serial bus (USB), or video graphics array (VGA) port. Others have a keyboard, mouse, or printer port. Serial PAC systems have RS232, RS422 or RS485 ports. IEEE 1394 or FireWire® (Apple Computer, Inc.) ports are also available.
Programmable automation controller (PAC) systems use popular communication standards and network protocols. Ethernet is a local area network (LAN) protocol that supports data transfer rates of 10 Mbps. Transmission control protocol/Internet protocol (TCP/IP) is the basis for standard Internet protocols. Controller area network bus (CANbus) is a high-speed, serial data network designed for harsh electrical environments and real-time control applications. DeviceNet uses the CAN network protocol to connect industrial devices to PAC modules. The process fieldbus or PROFIBUS is an open-communication standard used in factory automation, process automation, motion control, and safety applications. The MODBUS® (Modbus-IDA) protocol is an open-standard, vendor-neutral messaging structure for communication between intelligent devices. OPC defines a set of standard interfaces based upon OLE/COM technology and can be re-used by human machine interface (HMI) and supervisory control and data acquisition (SCADA) applications. Java® (Sun Microsystems, Inc.) database connectivity (JDBC) allows PAC modules to access to external structured query language (SQL) databases.
Selecting programmable automation controller (PAC) systems requires an analysis of regulatory requirements and special features. PAC systems for international markets should comply with Restriction of Hazardous Substances (RoHS), a European Union (EU) directive that requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of hazardous substances such as lead and mercury. The EU’s Waste Electrical and Electronics Equipment Regulations (WEEE Regulations) are designed to encourage the reuse, recycling and recovery of electrical and electronic equipment such as PAC systems.
Features of PAC:
Capable of real time communication
Fast boot speed
Achievable deterministic control
Open communication standards
Integrated development environment
Ability to run PC-based control software such as Visual Basic.NET, Visual C#, Embedded Visual
C++, SCADA software
Rich I/O Expansion Ability
Key Advantages of a PAC
These defining characteristics also describe the key advantages of using PACs in industrial applications:
A single controller with integrated software handles multiple functions across multiple domains.
Complex and changing requirements can be met with little additional cost.
Modular designs make expansion easier.
Networking and communication capabilities link disparate systems and provide more accurate
and timely data.
Total system cost is lowered, because integrated hardware and software are less expensive, and because development and integration time is reduced.
Modular design improves cash flow.
In summary, PACs now provide the multi-function, multi-domain, multi-tasking, modular, standards-based and efficient control, networking, and communications processor most suited to today's industrial applications.