Glossary of Common Terminology
Here is a handy listing of the common terminology used in the computer and controls industries:
CardBus: New 32-bit revision of the PCMCIA standard that brings PCI performance to portable PCs, including 132 Mb/sec throughput and DMA.
CompactPCI: A Eurocard configuration of the PCI bus for industrial applications.
DAQ (Data Acquisition): (1) Collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing; (2) Collecting and measuring the same kinds of electrical signals with A/D and/or DIO boards plugged into a PC, and possibly generating control signals with D/A and/or CIO boards in the same PC.
DCOM (Distributed Component Object Model): A set of Microsoft concepts and program interfaces in which client program objects can request services from server program objects over a network.
DMA (Direct Memory Access): A method by which data can be transferred to/from computer memory from/to a device or memory on the bus while the processor does something else. DMA is the fastest method of transferring data to/from computer memory.
Fieldbus: An all-digital communication network used to connect process instrumentation and control systems. It will ultimately replace the existing 4-20 mA analog standard.
Fieldbus Foundation: The organization developing a standard digital communication network (fieldbus) for process control applications. The network developed by the Foundation is referred to as the Foundation Fieldbus.
FireWire: See IEEE 1394.
HMI (Human-Machine Interface): The means by which an operator interacts with an industrial automation system, often a graphical user interface.
IEEE 1394: The shortened notation for IEEE standard 1394-1995, which defines a high-speed serial bus growing in popularity for connecting computers to peripheral video, memory, and instrumentation devices. The maximum transfer rate, currently at 400 kb/sec, is scheduled to increase in the future. (Also known as FireWire.)
Industrial Device Networks: Standardized digital communications networks used in industrial automation applications. They often replace vendor-proprietary networks so that devices from different vendors can communicate in control systems.
I/O (Input/Output): The interface, or the products that interface, to raw, real-world signals and transducers, including both analog and discrete, or digital, inputs and outputs. I/O products include the signal conditioning and acquisition functionality to connect directly to a variety of sensors and voltage and current sources.
MMI (Man-Machine Interface): see HMI.
Noise: An undesirable electrical signal. Noise comes from external sources such as the A/D power line, motors, generators, transformers, fluorescent lights, soldering irons, CRT displays, computers, thunderstorms, arc welders, radio transmitters, and internal sources such as semiconductors, resistors, and capacitors.
OLE (Object Linking and Embedding): A set of system services that provides a means for applications to interact and interoperate. Based on the underlying Component Object Model, OLE is object-enabling system software. Through OLE automation an application can dynamically identify and use the services of other applications to build powerful solutions using packaged software. With OLE it is also possible to create compound documents consisting of multiple sources of information from different applications.
OPC (OLE for Process Control): An open industry-standard device interface that provides interoperability between disparate field devices, automation/control systems, and business systems. OPC is based on ActiveX, OLE, Component Object Model (COM), and Distributed COM (DCOM) technologies.
PC Card: A credit-card-sized expansion card that fits in a PCMCIA slot, often referred to as a PCMCIA card.
PCI (Peripheral Component Interconnect): A high-performance expansion bus architecture originally developed by Intel to replace ISA and EISA. It has achieved widespread acceptance as a standard for PCs and workstations and offers a theoretical maximum transfer rate of 132Mbytes/sec.
PCMCIA: An expansion bus architecture that has found widespread acceptance as a de facto standard in notebook-size computers. It originated as a specification for add-on memory cards written by the Personal Computer Memory Card International Association.
PLC (Programmable Logic Controller): A highly reliable special-purpose computer used in industrial monitoring and control applications. PLCs typically have proprietary programming and networking protocols, and special-purpose digital and analog I/O ports.
Plug and Play ISA: A specification prepared by Microsoft, Intel, and other PC-related companies that will result in PCs with plug-in boards that can be fully configured in software, without jumpers or switches on the boards.
PXI (PCI eXtensions for Instrumentation): A rugged, open system for modular instrumentation based on CompactPCI, with special mechanical, electrical, and software features.
RTD (Resistance Temperature Detector): A metallic probe that measures temperature based upon its coefficient of resistivity.
SCADA (Supervisory Control and Data Acquisition): A common PC function in process control applications where programmable logic controllers (PLCs) perform control functions but are monitored and supervised by a PC.
Thermocouple: A temperature sensor created by joining two dissimilar metals. The junction produces a small voltage as a function of the temperature.
USB (Universal Serial Bus): A serial bus gradually replacing RS-232 on PCs because of its higher speed.