Programmable Automation Controller (PAC) Systems Information
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.
Communication Standards and Network Protocols
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® (Profibus International) 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 for programmable automation controller (PAC) systems include surge protection, visual indicators, watchdog timers, and real-clock timers. PAC systems with a reset button, integral power supply, and built-in web server are also available. Hot-swappable PAC systems allow the installation and removal of modules during operation.