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L ≤ 10 - 15 m
Frequency (MHz)
Magnetic field
Electrical field
Attenuation (dB)
Example of attenuation level of S3HF enclosures
The presence of 55% aluminium on the surface of the sheet metal ensures good
reflection of electromagnetic waves.
The graphic next to these lines shows the attenuation curves (dB) according to the
frequency (MHz).
Installation
According to the type of interference generated by the devices:
● Low frequencies, "conducted interference" (up to 30 MHz).
● High frequencies, "radiated interference" (higher than 1 MHz).
the rules to be taken into account relate to the choice of components that provide
the most economical solution to complete the installation.
Low-frequency interference
● Importance of the protection systems:
– Filters, overvoltage suppressor, isolating transformer for the power supply.
– Cable length.
High-frequency interference
● Importance of the installation method:
– Earth connections, cable length and section.
– Cable selection and rules, cable runs, connections.
– Enclosures and installation.
Specifics
Screen connections
It is recommended to earth screens at both ends. In addition, it is advisable to
increase the number of intermediate earth connections.
If the screen is only earthed at one end, there can be a considerable difference in
potential between the two ends. In addition, this screen will be ineffective against
external high-frequency interference.
Transformers
The transformer chassis must be mounted, metal to metal, on the reference
potential plate, that is, on a plain chassis supporting the equipment.
Earth plate or
reference potential
sheet connected to
the chassis
Poor
Excellent
Soldered
Earth connection
by the screws
Metal ground plate or
reference potential sheet
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