6.5 General Measures of Radio Interference Suppression for Re‐
lays, Contactors, Switches, Chokes and Inductive Loads
If, in conjunction with electronic devices and components, inductive loads, such
as chokes, contactors, relays are switched by contacts or semiconductors, ap‐
propriate interference suppression has to be provided for them:
● By arranging free-wheeling diodes in the case of d.c. operation
● In the case of a.c. operation, by arranging usual RC interference suppres‐
sion elements depending on the contactor type, immediately at the induc‐
tance
Only the interference suppression element arranged immediately at the induc‐
tance does serve this purpose. Otherwise, the emitted noise level is too high
which can affect the function of the electronic system and of the drive.
If possible, mechanical switches and contacts should only be realized as snap
contacts. Contact pressure and contact material must be suited for the corre‐
sponding switching currents.
Slow-action contacts should be replaced by snap switches or by solid-state
switches, because slow-action contacts strongly bounce and are in an unde‐
fined switching status for a long time which emits electromagnetic waves in the
case of inductive loads. These waves are an especially critical aspect in the
case of manometric or temperature switches.
48/65 Bosch Rexroth AG | Electric Drives
and Controls
Rexroth IndraDrive | Instruction Manual
EMC Measures for Design and Installation
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