PXI Chassis

- a summary of the PXI chassis with details of the relevant specifications including 3U and 6U sizes, power supply and slot functions.

This PXI tutorial is split into several pages each of which address different aspects of PXI and PXI Express test equipment and their operation:

The PXI chassis provides the means by which the whole PXI test system is able to be held together. The PXI chassis provides the services which the individual cards require for the operation. The PXI chassis provides everything from the mechanical card holders to the power supply and the air cooling required in such a densely packed volume.

The PXI chassis is standardised so that PXI cards and instruments will not only be able to mechanically fit, but electrically operate to their potential within the PXI chassis.

In order to be able to operate correctly, both cards or test instruments and the PXI chassis must conform to the standard. There are a number of salient features within the PXI specification that enable the cards and the PXI chassis to operate together.

Basic PXI chassis parameters

PXI chassis system is based around the Eurocard packaging system. This provides a number of advantages including a system that is already established. Furthermore the connectors that are used are the IEC-1076 style. The pins are on a 2 mm pitch giving a very dense connection system. In addition to this they are impedance matched to provide the required performance at high frequencies.

The PXI system supports the two sizes, namely 3U and 6U with the details outlined in the table below:

The 3U standard has two interface connectors. One carries the signals required for the 32-bit PCI local bus and the other carries the signals for 64-bit PCI transfers and the signals for implementing PXI electrical features. The 6U form factor defines modules that may carry up to two additional connectors for future expansion of the PXI specification. The larger card size also allows for a additional circuitry that may be required for some instruments.

In general the 3U PXI chassis and modules are more widely used. However the 3U modules can be fitted into a 6U chassis using a simple adaptor.

PXI chassis power capability

Although there is some difference between different types of PXI chassis modern ones conforming to the latest issue should be capable of providing supplies of +5V, +3.3V, +12V, and -12V.

A PXI chassis conforming to the 2.1 version of the PXI standard must be able to deliver 1 amp on the +12V and -12V rails, and 6 amps on the +5V rail for any peripheral slot. Fortunately most modules do not consume these levels of current as if all card slots drew current to the maximum level it might be possible to exceed the power supply rating. This factor should be remembered when fitting large numbers of modules as their current consumption should be noted against the power capability of the PXI chassis power supply.

Further pages from this tutorial
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