INTERCONNECTION
and the trend towards increasingly compact medical devices must also be considered in detail - with special attention paid to any reductions in the size of electrical medical equipment and inherent components. Further, interfaces specifically must be especially reliable for use at all times and may not permit any sources of malfunction. Potential influencing factors such as disinfectants, bacteria or spray water must already be taken into account during the design process and incorporated into the selection process for components and materials.
Essentially, the IEC 60601-1 requires that two means of protection for both patients and operators from electric shock must be applied in electrical medical equipment and systems
(2 MOPP and/or 2 MOOP). In other words: if one means of protection fails, the other takes effect. An effective solution here, for example, would be to double the clearance and creepage distances between conductors. As soon as contacts are installed in the insulation body of a connector, clearance and creepage distances are generated between the conductive components.
• Clearance distance:
The shortest distance between two contacts outside the solid insulation • Creepage distance:
The shortest distance between two contacts along the surface of an insulation body
A clearance distance collapses as soon as the voltage becomes too high for the distance between two contacts. If these clearance distances collapse due to an excessively high field strength, electric flash- arcs occur. Flash-arcs not only damage individual components such as connectors,
but also endanger the well-being of patients and operators and may cause damage such as burns, muscle paralysis, right up to cardiac arrest.
Creepage distances on the other hand tend to deteriorate gradually. Causes of this can be dirt and dust deposits on the insulation body or moisture which can precipitate onto the insulation body due to significant changes in temperature. This results in the flow of leakage currents on the surface of the insulation body caused by a partial or complete loss of its insulating function, may cause an electric shock for patients and operators with similar effects already mentioned.
Installation space Vs. Clearance and creepage distances If we compare general medical requirements with the specific requirements laid down in IEC 60601-1, it becomes clear that conflicts can result and this is clearly demonstrated when based on the example of a connector. Medical equipment OEM’s are constantly striving to reduce the size of their devices, as a consequence the related connectors also have to become more compact. The necessary increase in the clearance and creepage distances mean that connectors face the challenge of implementing high power transmission in space saving products.
If the voltage is increased, it influences the touch protection of the medical equipment, which in turn means that specific counter measures have to be put in place. This may mean, for example, that additional domes have to be added or the clearance distances between electrical conductors have to be extended. This example clearly shows that manufacturers of medical products repeatedly face the challenge of optimal use of the construction
space on the one hand and the fulfilment of the necessary means of protection stated in the IEC 60601-1 on the other. With regard to current, the contact diameter also plays an important role. If the current is increased, the diameter of the contacts must also be increased in order, for example, to counteract the resulting heat development. This in turn means that the construction size of the connector must be adjusted appropriately, at the expense of the existing construction space.
This has no influence on the IEC 60601-1, so long as the voltages are not increased respectively, the clearance and creepage distances within the connector do not change.
The plastic circular connector portfolio of the ODU MEDI-SNAP series includes over ten different receptacles which can be installed in medical equipment and systems. Due to reinforcements in the mating area, five of these receptacles fulfil the requirements in mated condition for the highest level of patient and operator protection of 2 MOPP and 2 MOOP in accordance with the IEC 60601-1. These receptacles achieve 2 MOOP in ambience with pollution degree 3. The other eight receptacles and in-line receptacles provide one means of protection for patients (1 MOPP) and also achieve 2 MOOP in ambience with pollution degree 2.
For example, if receptacles and in-line receptacles with only one means of protection are used in equipment together with power supplies which themselves have a means of protection installed in them, the medical end device then achieves as a whole 2 MOPP and 2 MOOP.
Apart from the measures which enable a MOPP or 2MOOP level on the connector itself, it is also possible to implement two of the means of protection stated in the IEC 6060-1 into several separate components within electrical medical equipment. In this way it is possible, for example, to integrate one means of protection into the power supply whilst the second is implemented within the connector. This has to be verified by the equipment manufacturer in the approval procedure, therefore it is even more important than before that OEM’s and their suppliers collaborate closely during the development of new medical electrical equipment and systems.
A full copy of the white paper is available at: https://www.odu-
uk.co.uk/fileadmin/redaktion/downloads/dow nloadcenter/Whitepapers/WHITEPAPER_IEC60 601-1_11_2018_EN_0811.pdf
ODU
www.odu-uk.co.uk
JUNE 2021 | ELECTRONICS TODAY 9
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