MEASUREMENT & AUTOMATION TECHNOLOGY GLOSSARY
This page provides a useful glossary of measurement and automation technology terms. An alternative glossary covering manufacturing terms is also available.Manufacturing Terms Glossary
CompactDAQ or cDAQ:
A DAQ hardware platform from National Instruments which is controlled by a PC via a USB interface. The unit consists of a chassis where up to 8 plug-in c-series I/O modules are inserted.
CompactRIO or cRIO:
A hardware platform from National Instruments which combines a realtime embedded computer, an FPGA and the range of plug-in c-series I/O modules together.
DAQ or DAS: Data Acquisition
The process of automatically gathering information from analogue or digital electrical signals into a device, such as a computer. A DAQ device often contains an analogue to digital convertor to change analogue electrical waveforms into binary computer data.
EtherCAT:
A special Ethernet version designed for automation applications, which provides a higher level of determinism. An EtherCAT expansion chassis exists for CompactRIO.
Ethernet:
A computer communications technology used for local area networks. Twisted pair Ethernet connections are supported by a wide variety of devices such as PC's, printers, PLCs, hard drives, set-top boxes and cameras.
FieldPoint:
A distributed I/O hardware platform from National Instruments designed for industrial monitoring and control. It consists of a backplane where a range of different signal and transducer I/O modules can be inserted, which are then controlled via either a realtime embedded computer within the system, or through a seperate desktop PC via an RS232 or Ethernet link.
FPGA: Field Programmable Gate Array
An integrated circuit consisting of a large number of software configurable logic elements. FPGAs combine the parallelism and reliability of hardwired logic circuits, with the more rapid development process of a software based system.
FPGAs can be programmed using a hardware description language, such as VHDL or Verilog, or through higher level tools including graphical environments such as LabVIEW.
GPIB: General Purpose Interface Bus
See IEEE-488
HMI: Human Machine Interface
Strictly, this is a method by which an operator can interact with a machine. When applied to computer-based measurement, monitoring or control equipment this typically refers to the interface between an operator and the computer program. This is usually in the form of a graphical display with some operator inputs, such as a keyboard, mouse, touch-screen or operator buttons. In this context, an HMI differs from a full graphical user interface in that it typically has a simplified layout designed to provide only necessary functionality. This ensures that the system can be operated efficiently without the hinderance of all configurable settings being visible to the operator.
HPIB: Hewlett Packard Interface Bus
See IEEE-488
IEEE-488:
A digital communications bus originally developed by Hewlett Packard in the late 1960s, which is still widely used today for communicating with a wide range instrumentation. IEEE-488 is a parallel communications bus which uses a 24 wire connection consisting of 8 data lines, 3 handshaking lines, 5 bus management lines and 8 ground links. Although originally developed by Hewlett Packard under the name HPIB, other instrument manufacturers started to adopt the bus, naming it GPIB. In 1975 the IEEE-488 standard was published formalising the electrical and mechanical properties of the bus; this was followed in 1987 by IEEE-488.1 which added command formats to the standard.
Instrument Driver:
An Application Programmer Interface (API) allowing a developer to control an instrument using a high level set of functions. Therefore, instead of having to send low-level commands to an instrument and interpret the responses, the instrument driver abstracts this level of complexity away from the developer - ensuring that applications are easier to develop and are less prone to errors.
IVI: Interchangeable Virtual Instruments
A standard for instrument drivers to ensure consistent functionality and software interfaces, independent of the instrument vendor. IVI Class Compliant drivers go one step further by allowing instrument interchangability within the same class. For example, application software could be developed to use an oscilloscope by using a generic IVI oscilloscope driver. The physical instrument could then be changed for a different model, or even a different vendor without changing the underlying code. This is a desirable feature in situations where obsolescence is a problem, such as the aerospace industry, where test applications may have a life expectancy of decades. The IVI specification, along with VISA and SCPI, is maintained by the IVI Foundation.
LabVIEW:
A dataflow programming language produced by National Instruments, which uses graphical block diagrams instead of text for its source code. LabVIEW is optimised for engineering operations such as data acquisition, control and automation, where it can significantly reduce development time compared to traditional programming tools.
More on LabVIEW | National Instruments LabVIEW Website
Simplicity AI have National Instruments certified LabVIEW Developers
LXI: LAN eXtensions for Instrumentation
Intended as the successor to GPIB, LXI uses Ethernet as the physical connection to external instruments (i.e. instruments not integrated within the computer). This increases data rates, simplifies wiring and allows the maximum distance between instruments and the host computer to be increased to tens of metres. Timing synchronisation and triggering over ethernet are also supported. In addition, LXI compliance mandates that an instrument must have an IVI Driver, thereby ensuring greater consistency in software programming. If the instrument matches one of the defined IVI classes, then the driver will be IVI Class Compliant.
Modbus:
A communications protocol for talking to PLCs via either RS485 or Ethernet.
PAC: Programmable Automation Controller
Used to describe platforms which combine the attributes of PLCs such as high relibility, realtime execution and rugged construction with faster evolving, more powerful technology from PCs. Product examples include the FieldPoint and CompactRIO
PDF: Portable Document Format
A common file format used for the exchange of documents which was originally created by Adobe Systems.
Simplicity AI have developed a PDF Toolkit for LabVIEW.
PLC: Programmable Logic Controller
A programmable real-time computer unit which is often used for industrial process automation. PLCs usually have I/O connection modules attached allowing them to be connected to variety of sensors and actuators. Modern PLCs are usually programmed via a PC based development program, using either a serial or Ethernet connection.
PXI: PCI eXtensions for Instrumentation
A platform for modular instrumentation based on the compactPCI standard. PXI uses a 4U high chassis which 3U instrumentation modules slot into. The chassis backplane carries a PCI bus which allows communication between the modules and either a controller in the chassis or a host computer, connected to it via a bridge. The PXI platform includes extensions specially designed for instrumentation, such as dedicated timing and triggering lines added to the backplane to synchronise different modules together.
PXIe: PCI Express eXtensions for Instrumentation
The successor to PXI, PXI Express has the same physical size as PXI, but utilises the faster PCI Express bus, allowing for 2GB/sec dedicated per slot bandwidth - enabling high speed data streaming from instrumentation where this was not previously possible. In addition, PXI Express provides more accurate and comprehensive syncronisation and triggering over traditional PXI.
SCADA: Supervisory Control And Data Acquisition
Refers to a large-scale, high-level data acquisition and control system - often used for monitoring an industrial process. Typically a SCADA system will monitor inputs and update control outputs at a slow rate (<5Hz), with high-speed, or real-time control operations being driven by a separate system.
The Compressor Test Cell Project is an example of a SCADA system.
TestStand:
National Instruments TestStand is a test management software environment which allows the development and execution of automated test sequences. The software is typically used in a production test setting, where it handles common operations such as sequencing of multiple test steps, calling test step code modules, looping and branching, results collection, limit checking, user management, operator user interface management, database logging and report generation. TestStand signifcantly reduces the development time of product test systems by providing these common components out of the box. Conversely, although it provides ready to run common test objects, they are also all highly customisable to the extent where they can be completely replaced with the developers own custom code if desired.
More on TestStand | National Instruments TestStand Website
Simplicity AI have National Instruments certified TestStand Developers and Architects
SCPI: Standard Commands for Programmable Instruments
A standard of defined command strings for controlling programmable instruments. The SCPI standard was an attempt to harmonise the variation in syntax and command structure between instruments and vendors. Many modern instruments follow the SCPI command structure and syntax for low level communication, although generally an instrument driver (such as an IVI driver) is used hide the raw commands from the programmer, allowing them to deal with functions and attributes instead.
TDMS: Technical Data Management Streaming
A standard data file format for storing streamed measurement data developed by National Instruments.
USB: Universal Serial Bus
Universal serial bus is a digital communications bus which is commonly used to interface peripherals such as keyboards, mice and flash drives to a host computer. USB is almost universally availabile on modern computers and offers higher convenience over RS232 or PCI due to its 'plug-and-play' and 'hot-pluggable' capabilies, and the fact that a computer chassis does not have to be opened up to install hardware.
Due to its high availablity USB is becoming a common interface for instrumentation and data acquisition devices, although there can be limitations where high performance or industrial ruggedness is required. USB is increasingly replacing RS232 connections on bench-top instruments, as RS232 ports are less commonly available on modern computers.
VISA: Virtual Instrument Software Architecture
VISA is a low-level I/O library allowing data communication over a variety of data busses. A standard software interface is presented, independent of the physical communication path. For example, this would allow the same software to be used whether communicating with a USB instrument or via GPIB. Typically, VISA forms the low-level I/O interface within an instrument driver (such as an IVI driver).