Programmable automation controllers (PAC) are compact industrial controllers used in motion control, machine control, machine vision, and general-purpose industrial control applications. They are functionally similar to programmable logic controllers (PLC), but provide the advanced software features of personal computers (PC). Programmable automation controllers or PACs are used in logic, motion, process control, and vision systems which require data logging, signal processing and other advanced software capabilities. According to the Automation Research Corporation (ARC), the company which coined the PAC acronym, programmable automation controllers (PAC) have five main features: multi-domain functionality; a single, multi-discipline development platform; flexible software tools that maximize process flow across machines or process units; an open, modular architecture; and compatibility with enterprise networks. 

Categories

Programmable automation controllers (PAC) can be divided into two categories: PAC systems and PAC modules. A PAC system consists of one or more PAC modules, each of which performs a specific function. Common types of PAC modules include: 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. Many programmable automation controllers or PACs include features such as watchdog timers, real-clock timers, visual indicators, reset buttons, or surge protection. PACs with an integral power supply or built-in web server are also available. Hot swappable PACs can be installed or uninstalled during normal operation. 

Backplane Bus Type

Programmable automation controllers (PAC) differ by backplane bus type and may have one or more backplane slots for adding input/output (I/O) modules. 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 PACs have an Ethernet, universal serial bus (USB), or video graphics array (VGA) port. Others have a keyboard, mouse, or printer port. Serial PACs have RS232, RS422 or RS485 ports. IEEE 1394 or FireWire^® (Apple Computer, Inc.) ports are also available.  

Network Protocols and Communication Standards

Programmable automation controllers (PAC) use many different network protocols and communication standards. Ethernet and TCP/IP are common types. 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^® (Profibus International) is an open-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 PACs to access to external structured query language (SQL) databases. 

Specifications

Programmable automation controllers (PAC) 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 PACs.