RACKS, CABINETS & ENCLOSURES FEATURE UP TO THE TASK
New challenges for enclosure solutions in test and measurement
Alan Cook, managing director, Foremost Electronics, looks at the best means of enclosing and protecting a PXI Express testing system
nVent Schroff offer the sort of enclosure suited to PXI systems
T
here are growing requirements for simulation, test and measurement
tasks that are changing the necessities for enclosure and cabinet solutions as well. This concerns the system architecture, with factors such as high computing power, fast data transfer, as well as mechanical properties such as improved EMC shielding, superior signal integrity and platform-based developments for the modularity of test and measurement systems. Depending on the application, it is important to choose a system architecture that provides the desired properties and interfaces. With test and measurement, there are multiple standardised system architectures acceptable for building corresponding systems. In addition, corresponding mechanical requirements must be taken into account.
THE VARIOUS, VERSATILE APPLICATIONS OF PXI EXPRESS PXI Express systems are suited for the tough requirements in simulations for autonomous driving, on test stands for function tests in the area of civil and military aviation technology, and for product tests of consumer electronics during the production process. Such complex products require test
systems with a high data throughput and precise clock and trigger signals for synchronising the functions of the test object. These devices can be easily integrated into industrial networks and offer enough data bandwidth to connect and synchronise the test devices to, and with the rest of the production line.
Additionally, detailed data is transferred for quality management as well as for documentation. Thanks to its fast data transfer rates with PCIe, paired with the implemented high-precision clock and trigger architecture, which synchronises the cards with each other, PXI Express is very suitable for such test, measurement and simulation tasks.
SYSTEM ARCHITECTURE AND MECHANICAL SYSTEMS PXI Express is an updated PXI platform, and provides the user with the widely adopted PCI Express bus. It’s based on the widespread 19 inch form factor and offers backwards compatibility with the proven PXI; up to x8 links, supporting a system bandwidth of up to 24 GB/s for acquiring and evaluating simulated and measured data. The PCI Express bus is expanded by one or more PCI Express switches to enable a larger measurement system with more than four slots. A PCIe-to-PCI bridge is required to operate the older PXI cards, on the parallel 32-bit PCI bus.
MODULAR DESIGN OF PXI EXPRESS SYSTEMS Any PXI Express system is subdivided into two areas. One area includes the plug-in cards that are selected in a wide variety of combinations specific to the application. These represent the actual target functions of the system. The second area consists of the PXI Express chassis. It provides the infrastructure required for operating the plug-in cards, such as the mechanical enclosure and power supply.
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CONSIDERING THE BACKPLANE AND HOW IT AFFECTS THE BUILD To ensure that the backplane can be quickly adapted, it is designed to be as passive as possible, and the PCI bridge, PCIe switch and clock functions are executed as separate modules and arranged on the rear side of the backplane, between or above the slots. As a result, a more compact structure is possible in comparison to active backplanes. Thanks to the modular concept, standard components can be used, and any PXI Express backplane configuration can be easily implemented. Depending on the area in which the PXIe systems are used, there are different requirements for modularity, durability and EMC characteristics. It is therefore advantageous when you can rely on a broad product portfolio of enclosures, sub-racks and cabinets that are established in the market.
LOOKING AT THE POWER SUPPLY It is necessary to ensure that the power adapters being used will be available, if possible, over the entire, anticipated product life cycle. This prevents costly recertification of the systems. For nVent, as an example, corresponding industrial-grade power adapters with the conventional PC voltages (3.3V, 5V, ±12V, and 5V standby) are used. Unlike the ATX power adapters used in the commercial area, such industrial power adapters are typically available for more than ten years. The switch-on and switch-off behaviour of the various output voltages are very important. Firstly, to ensure that the cards are in fact initiated correctly and all functions are detected by the system controller during the boot process. Secondly, it is necessary to prevent data loss or, in the worst case, damage to a card caused by uncontrolled switch-off when the device is shut down.
Foremost Electronics
www.4most.co.uk Tel: +44 (0)1371 811171
ELECTRONICS | NOVEMBER 2019 23
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