Precision and quality are a priority

The Carl Zeiss Group have introduced a new laser scanning microscope which sets a new standard in fluorescent microscopy. The demanding electronics for the appliance were developed together with hema and assembled in a cabinet by the electronic enclosure specialist Schroff.

Carl Zeiss is a leading world wide group of companies in the optical and opto-electronic industry. The high-end laser scanning microscope LSM 510 META, recently introduced to the market, offers clearly improved possibilities especially to users in the biomedical research sector thanks to a new detection process, which uncovers the complex relationships and interactions of cellular structures and components and can follow them in living cells and tissues. Furthermore the appliance is suited for the research of structural surfaces like metals. Here it delivers information about the chemical make up, mechanical stress and structural amalgamation.
Hema, with 50 employees and more than 20 years experience, specialises in the development and manufacture of electronic components and systems for the use in equipment and machinery in the areas of industrial production, research and development.

Universal enclosure with EMC shielding

As there are different microscope variants available at Zeiss, hema decided to rely on the proven 19" industry standard, which allows variable assembly. In principle the control is based on a unified enclosure platform, a 6U VME backplane, power supply, as well as varying boards by hema. With Schroff's propac, Zeiss and hema chose a universal and economic enclosure, which principally can be used as table top, tower or portable version. The case consists of a one-part aluminium die-cast front frame, to which aluminium side panels are screwed. This construction guarantees an extremely stable assembly as well as very precise manufacture with negligible tolerances. This plays an important part in view of the subject EMC (electromagnetic compatibility), which is also essential for hema.

To protect the electronics of the microscope built into the case from high frequency electromagnetic radiation interference and to avoid emissions, a closed shield has to be created.The case must have as small openings as possible. The rule of thumb for shielding up to 1Ghz is: slots have to be smaller than 1/10 of the wave length, so that the enclosure is sufficiently sealed. The general process is to connect side, top and base panels with each other conductively. Here the rule applies: 'the smaller the mechanical tolerances of the individual parts, the better the continuous conductivity'. Even if the enclosure with all cover plates forms a well shielded system, under no circumstances must the front panels be forgotten. One opening at the front or two neighbouring front panels without EMC seals can ruin the rest of the measures. At hema the Schroff front panels with integrated HF spring seals are used. With regard to LCDs or glass elements, the market offers solutions which have been interspersed with metal fibres, and guarantee sufficient shielding.

Fire protection and individual design incorporated

The side panels of the propac have a 10 mm hole mounting pitch which facilitates the internal assembly according to IEC 60297-3. Furthermore screw channels in side panels make the mounting of chassis plates much easier, without threaded inserts or screws being required. For the airflow the case has free spaces below and above the assembled 19" subracks, which guarantee sufficient airflow even when backplanes and EMC shielding has been built in. Generally various fans for the cooling of the electronics of the microscope are integrated into the rear panel. The cool air is taken in through perforations at the base, flows via the boards to the top and is then expelled at the rear. A marked noise reduction was achieved when additional openings for the airflow were added to the backplane. Here also the Fire Protection Standard EN60950 must be observed, which stipulates that in case of a fire no melting plastic is allowed to drip from the subrack, meaning that no holes larger than 2 mm are permitted. Schroff has such a perforated base plinth as well as a metal mesh as drip guard for plastic.

As a standard the electronic packaging specialist offers customer specific design elements for its propac case, with which the user can provide an individual feature to his enclosure. For Zeiss it meant avoiding time consuming and expensive re-spraying, they simply chose decorative strips in Zeiss blue.