PMC-2 Instruction Manual
Page 30 BA * PMC-2 * EN * 01/98
4.4.2 Electromagnetic Tolerance
In general
To control and regulate motors, the mains voltage is stored in the DC-circuit of the PMC-2 by ac-dc
conversion. This stored energy is fed to the motor by deliberate switch-on and switch-off of six
semiconductor switches. The steep rise and fall of the current poses substantial demands to the
insulation ability of the motor winding. Another important aspect to be considered is electromagnetic
tolerance with regard to other system components. The high steepness of flanks of the tacted voltage
creates harmonic oscillations of great intensity up to the high-frequency range.
Therefore the following rules for electromagnetic tolerance must be observed:
• For installation, choose the lowest-possible earthing option (e.g. unpainted mounting board
of the switching cupboard).
• Contact on the largest possible surface (skin effect). If necessary remove existing paint to
enable large-surface contact.
• From the central earthing point, lay earthing wires to all connections in a star structure.
Earthing loops are not admissible and can cause unnecessary distortions.
• Use shielded cables only
• Only large-surface shield transitions are admissible.
• Contacting of shields by PIN contacts of plugs is not admissible.
• At all means observe switching proposals.
• Cut motor cables to minimum length.
• Do not lay cable loops in the switching cupboard.
Installation
CAUTION
The following installation rules must be observed to exclude the
consequences of excessive distortion effects as far as possible.
In connection with electronic controls, no inductive loads whatsoever must be switched without
appropriate shielding.
Appropriate shielding for dc-operation is achieved by arranging recovery diodes and for ac-operation
by arranging commercially available deleting elements compatible with the contactor used.
Only the shielding element mounted immediately at the inductivity serves its purpose. In any other
case the switching pulse may even emit increased interference via the cables of the shielding
element. It is much easier to avoid sources of interference than to eliminate the effects of existing
interference.
In no case must contacts switching unshielded inductive loads be placed in the same room as the
PMC-2. The same goes for cables leading unshielded switched inductivity and cables guided parallel
to them. The control must be separated from such “disturbance” by a faraday cage (own section in the
switching cupboard).
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