Agilent Technologies LXI manual Rack space, Distributed systems

7. Rack space

An LXI-based functional test system could be assembled in a rack as small as 750 mm tall (Figure 5). This space efficiency is due in part to LXI-based devices such as an eight-slot switch/measure unit with a built-in DMM (second position in rack) and a 1U modular power system (lowest position in rack).

To achieve maximum density, system developers often use cardcage-based instrumentation. With VXI, a C-size cardcage can hold up to 12 high-performance

instruments in about 6U, but this is often an expensive solution. PXI also provides high density, but its compact 4U size has four key shortcomings that are addressed by LXI:

Card size: Due to PXI card size, it may be necessary to use more than one slot to achieve the needed functionality. LXI instruments, on the other hand, can be created in a variety of sizes to ensure they fulfill their intended use.

Shielding: PXI cards are sus- ceptible to interference. For example, a Signal Conditioning eXtensions for Instrumentation (SCXI) power supply that emits high levels of magnetic inter- ference can lower the per- formance of an adjacent PXI DMM, potentially lowering DMM performance by a full digit of resolution. LXI devices are inherently shielded because they are fully self-contained.

Figure 5. With LXI, a functional test system can fit into a rack that is just 750 mm tall.

Cooling and power: Cardcages must provide sufficient cooling and power supply capacity to handle a maximum number of instruments or relays at one time. In demanding systems, it may be necessary to upgrade to one or more higher-cost mainframes capable of providing the required cooling and power. Automotive electronics applica- tions also often require instru- mentation output voltages that exceed the voltage capability of many PXI mainframes. LXI instruments are generally designed to provide the required power, voltage and cooling for their target application.

8. Distributed systems

Automotive production test systems typically co-locate all instruments. However, there is an inherent benefit to applica- tions such as durability test systems, R&D test systems and production validation systems when operators can place LXI instruments where the mea- surement needs to be made.

Production test systems also can benefit from a remote test- head. With off-the-shelf LXI switch modules, it is possible to create a test fixture that automatically adapts to any engine control module coming down the line, for example.

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