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The Alphabet Soup of Test-Instrument Standards

Industry insiders have a tough time deciphering the range of acronyms associated with the automation of test instruments. To help improve your fluency, here is a rundown of the major standards. The underlying intent is to give you a sense of how these all work together, perhaps helping you conquer the world of computer-based instrument control. This is necessarily an incomplete list.

AXIe: A new standard based on Advanced TCA, short for Advanced Telecom Computing Architecture or ATCA. ATCA is used in today’s computer servers and offers a mid-sized modular architecture for instrumentation. AXIe enhances ATCA with the clocks and triggers needed for test. From a software standpoint, AXIe looks much like PXI Express. www.axiestandard.org

GPIB: General-Purpose Interface Bus; often called HP-IB (HP invented this bus in the 1970s) or IEEE 488. This was the first dedicated bus for computer-to-instrument communications, and for 30 years GPIB has been the most common way to connect instruments to a computer. Two additions, 488.1 and 488.2, include extensions for basic syntax and format conventions. www.ieee.org

IEEE 488: Also known as GPIB.

IVI: Interchangeable Virtual Instruments, a software standard for instrument-to-computer and instrument-to-instrument communications. IVI drivers are available to allow programming from Windows-based environments. www.ivifoundation.org

LXI: LAN eXtensions for Instrumentation, leveraging the Ethernet (LAN) architecture to connect instruments and computers. Many view LXI as the successor to GPIB. It is a comprehensive standard covering LAN, web pages, instrument drivers, cooling, interference, and form-factor recommendations plus extensions for precision timing and triggering. www.lxistandard.org

PXI: PCI eXtensions for Instrumentation which embed the Peripheral Component Interconnect. PXI is a compact, modular, high-speed test architecture. It leverages CompactPCI (cPCI), an industrial form of the PCI bus. Although the standard defines several sizes, compact B-size cards are the dominant implementation in test applications. www.pxisa.org

PXI Express: Similar to PXI but uses the PCI Express (PCIe) and cPCIe specifications as a base. PXIe provides faster bus throughput and other performance enhancements. Additionally, the standard supports hybrid mainframes that can accept various combinations of PXI and PXIe cards. www.pxisa.org

SCPI: Standard Commands for Programmable Instrumentation. SCPI, pronounced skippy, was introduced to provide a standard set of instrument commands in ASCII format to control instrument functions and behaviors. SCPI was developed as an extension to IEEE 488 in part because GPIB never standardized the syntax of instrument commands. SCPI continues to be used as a low-level language on many instruments. www.ivifoundation.org/scpi/default.aspx

USBTMC: USB Test and Measurement Class, which includes the Universal Serial Bus. USBTMC provides the protocol for instruments to communicate with computers via USB. USBTMC-USB488 extends basic connectivity to provide GPIB-style commands over the USB bus. This enables the USB port on many instruments. www.usb.org

VISA: Virtual Instrument System Architecture, a standard interface for computer drivers to allow instrument communications. VISA connects various types of buses such as LXI, GPIB, or PXI to the computer operating system and enables an instrument driver such as IVI, SCPI, or VXIplug&play to communicate with the computer through the bus. www.ivifoundation.org

VXI: VME eXtensions for Instrumentation based on the VERSAmodule Eurocard (VME). VXI is a mid-sized architecture for modular instrumentation. The standard defines four card sizes, but C-size VXI dominates today’s market. The VXI specification is extensive, specifying card sizes, backplanes, cooling, shielding, EMI, and so on. It has achieved broad adoption in military test applications. www.vxibus.org

VXIplug&play: A driver architecture developed within the VXI standard and expanded to encompass other instrument types. Similar to IVI-C drivers, VXIplug&play drivers became necessary because SCPI’s ASCII format was not practical for modular, register-based architectures such as VXI and later PXI. www.ivifoundation.org


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