The failure of IT systems can cause damage costing millions. The demands on the availability of systems are enormous, particularly for telecommunications: many applications must be available for 99.999% of the time. This means that in one year a down time of just five minutes is allowed.
For satellite applications, the number of nines after the decimal point is increased to five. Such high availability values can only be achieved if repairs and service work do not cause any system disruptions.
The keyword is “hot-swap” and it stands for the exchanging of processor cards while the system is running.
With a hot-swap sequence, the software must first shut down the processor and save all the necessary data. In a second step, the electrical connections are disconnected.
Only then can the slot card be mechanically removed. It is essential that the power supply is not disconnected until the processor has been completely shut down.
The insertion of the card must also be executed in a controlled manner. When the start-up sequence begins, the slot card must be locked into its correct position, and all electrical connections must be established and the power supply stabilised.
Ejector handle controls hot-swap sequence:
The basic hot-swap process involves a trained technician manually shutting down the board and removing the unit from the configuration of the overall system.
The full hot-swap sequence automates this task: the unlocking of the ejector handles on the plug-in unit activates a microswitch, which gives the signal to shut down the processors.
When the card is inserted, the activation of the microswitch initiates the start-up sequence.
In order to guarantee the high level of availability of the systems, the hot-swap process must run in a controlled and reliable manner.
The central component here is the ejector handle. Its function is not restricted to the physical insertion and removal of the plug-in unit. The component controls the hot-swap sequence.
In accordance with PICMG 3.0 (Basic standard for AdvancedTCA), the hot-swap sequence is controlled via a microswitch on the front panel or on the PCB (Printed Circuit Board).
Two options are provided for the activation of the switch: either a metal control curve on the locking mechanism of the ejector handle or a specially installed switching pin in the middle of the lever presses on the lug of the microswitch when the lock is released.
This configuration has its dangers: depending on the construction of the ejector handle, the board can be mechanically released even as the microswitch is activated.
This does not guarantee that sufficient time remains for the processor to be shut down completely before the electrical connections are disconnected.
To make matters more difficult, the switching points of the microswitch can not easily be adjusted, since the switch travel is usually less than 1 mm.
Problems can also occur when inserting a plug-in unit. The microswitch is activated as soon as the ejectors handle locks - without checking first whether the inserting procedure has been completed.
Ejects in two stages:
With the ATCA Ergonomic Handle, ELMA offers a solution which ensures that the hot-swap sequence runs perfectly smooth.
The two-stage eject mechanism separates the switching and eject functions: the user first releases a sliding button (locking mechanism) and thus activates the microswitch. The plug-in unit still remains in position.
The processor is shut down via the signal from the microswitch. This usually takes a few milliseconds only. The AdvancedTCA standard specifies a blue light-emitting diode on the front panel that indicates the end of the process.
Now the electrical connections can be disconnected and the board physically removed. To do this, the technician moves the lever down or up.
Due to the elongated shape of the lever, not much effort is required. This two-stage eject process ensures that the plug-in unit is not taken out until the board has been properly shut down.
Also, it is not possible to release the plug-in unit inadvertently, since the lever lies close to the front panel when closed. The ATCA Ergonomic Handle also ensures that the plug-in unit can not be shaken loose.
Series of tests have shown that the cards even remain in position when subjected to fast and strong vibrations and that the microswitch is not unintentionally activated - even if the locking screw is loose.
Above and beyond the standard:
ELMA goes further than the AdvancedTCA standard with the development of the ATCA Ergonomic Handles.
With the injector and ejector handle, microswitches can not only be activated on the front panel and on the PCB.
The ATCA Ergonomic Handle available from Dedicated Systems provides the possibility of installing the microswitch to the ejector handle. This configuration has been available from ELMA for many years for the IEEE injector and ejector handles.
The integration of the microswitch increases the security and reliability of the hot-swap process.
When installing the microswitch on the front panel or on the board, not only the manufacturing tolerances of the individual components play an important role, but also the installation positions of the printed circuit board, the cut-out at the side of the front panel, and the positioning of the switching pin on the ejector handle.
A trouble-free switching function is also dependent on a long tolerance chain and on the precision with which the components are positioned.
ELMA circumvents this tolerance chain. By integrating the microswitch in the ejector handle, the hot-swap function is no longer allocated to several components. It is an integral part of the ejector handle and can be tested before installing the card.
This also leads to a simplification of the production processes for the customer. The front panels require no cut-outs at the side for operating the microswitch and can be produced and installed more cheaply due to the reduced manufacturing tolerances.
Installation times can also be reduced: The ATCA Ergonomic Handle can be simply and quickly fixed to the front panel with just two screws.
Moreover, the centring pin and locking screw are integrated in the component.
The new ejector handle thus provides all the necessary accessory elements in addition to the switching and eject functions. The ATCA Ergonomic Handle also has advantages for the manufacturer of the plug-in units. He is more or less free to position the components on the printed board as he chooses, since the microswitch is connected by cable.
Design and ergonomics:
The large number of plug contacts on AdvancedTCA boards results in large plug and pull forces. This makes great demands on the mechanics of the ejector handles.
Up to 500 N must be overcome when inserting or withdrawing the plug-in units - a task that an engineer carries out frequently during the development phase.
In designing the new injector and ejector handle, ELMA has therefore paid attention to the possible ergonomics. When the sliding button is activated, the elongated lever is turned forwards through 10° and locks in position.
The technician can open the lever further without exerting much pressure and take out the board. The proper release and unlocking of the plug-in unit is confirmed each time with a clearly audible and tangible click.
The design of the handle also includes a labelling field, which the customer can use for his own purposes.