ELECTROMAGNETIC INTERFERENCE
Basic principles Guidelines for preventing electronic equipment from malfunctioning are produced by organisations such as the Comité International Spécial des Perturbations Radio-électriques (CISIPR) and the International Electrotechnical Commission (IEC). For example, the electromagnetic immunity of medical equipment is specified in parts 1-2 of IEC60601-1-2: 2014 Medical Electrical Equipment. However, the electromagnetic environment in which such equipment operates is not always favorable either. It is therefore necessary to consider the electromagnetic environment in the area where the equipment is used. The guidelines propose the following principles for a desirable electromagnetic environment for medical and welfare facilities: l electrical independence or separation of the equipment from other electric systems
l suppression of electromagnetic waves (or radiating electromagnetic fields)
l suppression of magnetic fields l suppression of conduction noise (insulation of the building structure from power supply and grounding systems)
l safety from malfunction of the equipment and security against intervention or intrusion from outside.
The most important of these points is electrical separation; it is essential to configure electric and electronic facilities and systems as separate groups according to their function and to prevent interference between the groups. Usually, power supply systems are carefully designed to prevent interference; for example, the power supply systems for air conditioning and elevators, which generate noise, are arranged separately to those used for precision medical devices. However, building grounding systems are not always adequately studied and designed and precision instruments are often connected to noise sources through a common grounding system or they may be linked electrically to noise sources through the building structure, often leading to noise interference. Inadequate grounding, which is likely to lead to problems with noise, also makes it difficult to identify the cause.
Lightning strike A lightning strike can result in one of the most severe electromagnetic disturbances, although common mode noise emitted from inverters is the cause in many cases. To ensure the stable operation of medical and welfare facilities, it is vital to understand these issues and take measures to prevent them. Protective measures that can be taken against lightning are specified in IEC
IFHE DIGEST 2019
Figure 1. A conventional lightning protection system for a building.
Figure 2. The basic propagation routes of the noise from a panel containing one inverter or more.
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