VXI

VXI, short for VME eXtensions for Instrumentation, is a modular instrumentation bus standard that extends the VMEbus to support automated test equipment. Developed in the 1980s by the VXIbus Consortium, it standardized the interconnection, timing, and control required for multi-module measurement systems. The standard defines physical form factors, backplane architecture, and electrical interfaces to facilitate interoperability among instruments from different manufacturers.

A typical VXI system consists of a chassis housing a VXI backplane, a system controller, and multiple VXI modules such as digitizers, switch matrices, signal generators, and condition monitoring modules. Modules are implemented as 3U and 6U Eurocards that plug into the backplane, which provides the data and control busses as well as dedicated timing and trigger lines. The architecture supports synchronous operation across modules and allows high data throughput within a single instrument system.

Key features include hardware triggers, timing references, and interrupt or event signaling to coordinate measurements and data transfers across modules. The backplane and timing mechanism enable synchronized multi-channel acquisition and processing, making VXI well suited for automated test equipment, aerospace and defense testing, and other complex instrumentation environments.

Over the years, VXI has faced competition from newer standards such as PXI and LXI, which offer different form factors and networking approaches. Despite this, VXI remains in use for legacy systems and applications requiring precise timing, tight module coordination, and a durable, modular rack-based platform. Vendors continue to supply VXI modules and chassis to maintain compatibility with existing installations.