EMC Question of the Week: January 15, 2018
Coupling from low-flying planes at 400 Hz disrupts a particular sensor in an automotive system affecting the navigation system. The coupling mechanism must be,
- common impedance coupling
- electric or magnetic field coupling
- radiated coupling
- either "a" or "c"
Answer
The correct answer is "b". The coupling cannot be common impedance (i.e. conducted) coupling, because there is no wired connection between the low-flying aircraft and the automotive sensor. The coupling cannot be radiated, because the source is too close to the victim at the frequency of the interference. [Note that the wavelength of the fields at 400 Hz is 750 km.] Therefore, the only remaining options are electric or magnetic field coupling. A quick examination of the sensor would probably reveal which type of coupling was more likely. Capacitive sensors (e.g. most acceleration sensors) tend to be more sensitive to electric fields. Hall-effect sensors and inductive sensors tend to be more sensitive to magnetic fields.
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