Protection against electromagnetic disturbance

To avoid interference when recording EMGs (electromyograms), ECGs (electrocardiograms) or EEGs (electroencephalograms), the magnetic induction of mains-frequency magnetic fields at the patient's position must not exceed the following values:

1 · 10−7 Tesla = 0.1 μT for EMGs
2 · 10−7 Tesla = 0.2 μT for EEGs
4 · 10−7 Tesla = 0.4 μT for ECGs

ECG thresholds are generally met if the following minimum distances in all directions between the electrical equipment item (source of interference) and the patient’s position are observed:

  • 6 m minimum distance for inductive equipment of elevated performance such as transformers in the high-voltage installation and stationary motors up to 3 kW;

  • 3 m minimum distance for multi-core cables and lines of the high-voltage installation with a cable cross-section of 10 to 70 mm2, 6 m minimum distance for 95 to 185 mm2, and 9 m minimum distance for cross-sections larger than 185 mm2

  • 0.75 m in case of medical supply units.

For single-core cables and track systems, greater distances may be required.

Magnetic control gear and electronic control gear for fluorescent lamps as well as LED control gear do not present realistic interference hazards for EEG and ECG measurements.

EN ISO 11197 contains a block diagram of a measuring arrangement for magnetic induction. The repeater in this block allows for the use of an ECG device with appropriate calibration (see also chapter 1.4.6 "Lighting of rooms in the healthcare sector").

Figure 2.69: Measuring arrangement for magnetic induction according to EN ISO 11197
1 standardised testing coil
2 resistances
3 condensers
4 repeaters
5 output voltage 0.1 V, accordingly 1 μT