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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.
6
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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