Feature Cases & enclosures The evolving world of MicroTCA A MicroTCA sub-specification called MicroTCA.4 – MTCA.4 – was set up for the
advanced physics community, but is now finding interest in other market segments such as test and measurement. Christian Ganninger, product manager for systems at Pentair in Germany, and David Martin, managing director at Pentair-Schroff UK, explain
esearch institutes whose activities are concerned with photons, elementary particles and astro-particle physics, build and operate complex physical systems such as particle accelerators, x-ray lasers and neutrino scales. Such experiments have frequently been controlled using VME systems, but a few years ago a group from several research institutes began to look for a suitable platform for the next generation of control systems; and committed themselves to the xTCA standard.
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Although MicroTCA and AdvancedTCA are well suited as platforms for these applications, both lack certain features. To implement these, the xTCA base specification was created in 2009 within the PICMG working groups in order to extend the standard to include these extra functionalities. While in AdvancedTCA only additional signals in zone 3 were defined, it was necessary to adapt the MicroTCA specifica- tion to a greater extent. This was then realised in the sub-specification MTCA.4, “Enhancements for Rear I/O and Precision Timing”.
The specification: why MTCA.4?
The researchers settled on xTCA due to the carrier and shelf management, which both AdvancedTCA and MicroTCA specifications offer. Redundancy also allows elements to be swapped while the system is in operation. The integrated carrier and shelf management makes it possible to monitor the status of all components in the system at any time and to respond to error statuses. It also allows the system to be remotely maintained, with operational status being moni- tored from a control room – a benefit for particle accelerators, for example, since no access is permitted to any part of the accelerator ring, where the control and monitoring systems are installed, during experiments. Other features, however, were also required that were not implemented in the MicroTCA base specification. For a start, additional rear transition modules (RTMs) are necessary to accommodate the large number of I/Os on the rear front panels and to physically separate digital and analogue I/Os. In addition, the advanced physics community requires high-precision clock and trigger signals. The PICMG working group ‘xTCA for Physics’ was therefore set up, and this has now defined a suitable MicroTCA sub-specification known as MicroTCA.4. This specification is also of interest to other market segments in industry, since the same requirements are often also found there – such as in testing and measurement. The specification has since been renamed ‘Enhancements
for Rear I/O and Precision Timing’ in order to indicate its suitability for other applications as well. As an active member of this PICMG working group, Pentair provided support during development of the specification by pro- ducing the first Schroff systems.
Technical challenges
The rear I/O area and the board cage at the rear required specific further development. The idea was to feed in sensi- tive high-frequency analogue signals to the rear of the system in the rear I/O section, to process them, convert them into digital signals and then to pass them forward to the processor units in the front board cage. The biggest challenge here was
Instrumentation NOVEMBER 2013
19" MicroTCA.4 system with 12 AdvancedMC slots
realising the rear I/O board cage in connection with the MicroTCA direct connector. Extensive tolerance calculations were necessary to verify that front and rear connectors were securely inserted and that the MicroTCA connector contacted securely. Additionally, management for the rear transition modules and ventilation for the rear I/O area were defined. The module size used in the front area was the double mid-size module (height 150mm, width 4 HP, depth 180mm). The mid-size width allows the maximum possible number of twelve AdvancedMC modules including two MCHs (MicroTCA carrier hubs) and up to four power modules to be fitted into one 19” wide system. For the modules on the rear, the rear transition modules, the same area was selected as for the front module. The MicroTCA.4 system is therefore about twice as deep as a MicroTCA.0 system.
The front modules are connected directly to the rear ones via a connector. Although this sounds simple, it can lead to difficulties with regard to the length tolerances and the centring or fixing of the modules in the system. In a MicroTCA.0 system the front modules are centred through the connector positioned on the backplane and held in this position by the handle of the front panel. In the MicroTCA.4 system, this solution would cause the AdvancedMC module to move away from the centre position when the rear module is inserted, leading to possible discontinuities or short circuits in the MicroTCA connector.
The designers have come up with a solution that is as simple as it is effective. Use is made of the special screw fitting of the AdvancedMC modules defined in the Rugged MicroTCA specification MTCA.1, which holds the AdvancedMC securely in its centred mounting position. Most important now, how- ever, is the order in which the front and rear modules are fitted. First the front module is inserted and the front panel bolted into place. Next, its associ- ated rear module is inserted from the rear and bolted tight.
Front and rear modules are inserted directly
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