LXI Instrument Classes
- overview of the different LXI Instrument Classes detailing the capabilities of the different classes.
Not all LXI test instruments have the same level of functionality.
In order to be able to design and build devices that provide the required level of functionality, while still conforming to the overall standard, three classes of LXI test instruments have been defined.
By defining LXI classes, it is possible to have guidelines about the capabilities of the different test instruments that may be connected within a system.
LXI instrument classes
There are three functional classes into which LXI instruments can be placed:
- LXI Class C: This LXI class is the most basic. Instruments falling into this class provide a standardised web browser interface that conforms to the LXI standard. The devices in LXI class C do not need to support either a wired trigger bus, or the IEEE 1588 timing protocol.
This LXI class is particularly applicable to instruments that were originally not intended for LXI applications have had their designs updated to enable them to interface into LXI systems without the need for complete functionality, especially in terms of triggering and timing. Typical applications may include small sensors where Ethernet instrument capability is required, but cost and size are key factors.
- LXI Class B: This LXI class provides all the class C features plus the additional features of the trigger or synchronisation API and support for the IEEE 1588 timing elements.
The trigger API allows devices to execute trigger functions equivalent to those available with GPIB. Captured data can be time-stamped and this allows the system to trace when the data was captured.
- LXI Class A: This class of LXI instruments is the most comprehensive. It incorporates all the features of Class B, and hence class C, and on top of this it also supports a wired trigger bus interface. The Wired Trigger Bus, WTB, enables much greater levels of accuracy to be obtained from triggering than by other methods available in Class B. The trigger accuracy is only limited by the physical limitations of the cables and the interface circuitry. In essence it is broadly equivalent to the trigger functions available with modular instruments, although the cable lengths introduce additional delays.
These LXI class descriptions should only be taken as broad overviews. Many LXI instruments have been developed that do not neatly conform to these LXI classes as they incorporate functionality require for the envisaged function of the instrument. The functionality may therefore contain aspects that do not completely match the LXI classes defined above.
By Ian Poole
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