Electronic Design

The Future Of Modular Test Systems

While it has been designated as the successor to IEEE 488 GPIB, LXI isn’t likely to make GPIB go away. GPIB is still widely used because of its low cost, long successful history, ruggedness, and reliability. LXI simply extends the range and speed for instrument interconnections and adds a critical timing and synchronizing capability not available in GPIB.

Neither will LXI encroach on PXI turf, which addresses a different set of needs in the modular instrument world. What LXI does is provide the test engineer with a new option that may or may not be a better fit to the test application. While PXI is probably a better choice for low-end data acquisition and test applications, LXI targets customers who want to build rack and stack automated test systems for electronic devices.

The main difference between PXI and LXI systems is that in a PXI chassis, the instrument acquires the test data and transmits it over the internal bus to the built-in PC, where it is processed by virtual instrument software. The Multi-chassis eXtension for Instrumentation (MXI) interface developed and supported by National Instruments can be used to connect to an external PC or laptop used for the processing, replacing the internal chassis PC.

Remember that the LXI instruments are complete instruments that do the acquisition and processing internally. Then they use Ethernet for programming and control to transmit the result for viewing, collection, storage, or whatever. PXI instruments are software-based virtual instruments.

Another big difference is that all the connections to the test setup are on the front panel of the PXI modular instruments. In the LXI chassis, the test setup connections are on the front panel while all the Ethernet and other ports are on the back. Keeping these separate makes interconnections more flexible, where noise can be minimized and signal integrity improved.

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