Glentek Inc. 208 Standard Street, El Segundo, California 90245, U.S.A. (310) 322
SMA7130, SMA71075 and SMA71100 MANUAL
The following suggestions are recommended for all installations.
1. Motor cables must have a continuous shield and be terminated at both ends. The shield must
connect to the ground bus bar or drive chassis at the drive end, and the motor frame at the
motor end. Use of a properly shielded motor cable is essential to meet European EMC
requirements.
2. Signal cables (encoder, serial, and analog) should be routed away from the motor cable and
power wiring. Separate steel conduit can be used to provide shielding between the signal and
power wiring. Do not route signal and power wiring through common junctions or raceways.
3. Signal cables from other circuits should not pass within 300 mm (1 ft.) of the drive.
4. The length or parallel runs between other circuit cables and the motor or power cable should
be minimized. A rule of thumb is 300 mm (1 ft.) of separation for each 10 m (30 ft.) of parallel
run. The 300 mm (1 ft.) separation can be reduced if the parallel run is less than 1 m (3 ft.).
5. Cable intersections should always occur at right angles to minimize magnetic coupling.
6. The encoder mounted on the brushless servomotor should be connected to the amplifier with
a cable using multiple twisted wire pairs and an overall cable shield. Encoder cables are
offered in various lengths that have correct terminations.
Persistent EMI problems may require additional countermeasures. The following suggestions for
system modification may be attempted.
1. A ferrite toroid or “doughnut” around a signal cable may attenuate common mode noise,
particularly RS-232 communication problems. However, a ferrite toroid will not help differential
mode noise. Differential mode noise requires twisted wire pairs.
2. Suppress each switched inductive device near the servo amplifier. Switch inductive devices
include solenoids, relay coils, starter coils and AC motors (such as motor driven mechanical
timers).
3. DC coils should be suppressed with a “free-wheeling” diode connected across the coil.
4. AC coils should be suppressed with RC filters (a 200 Ohm 1/2 Watt resistor in series with a
0.5 uF, 600 Volt capacitor is common).
Following these guidelines can minimize noise problems. However, equipment EMC performance
must meet regulatory requirements in various parts of the world, specifically the European Union.
Ultimately, it is the responsibility of the machine builder to ensure that the machine meets the
appropriate requirements as installed.
APPENDIX C: EUROPEAN UNION EMC DIRECTIVE
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