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SMA7130, SMA71075 and SMA71100 MANUAL
Immunity to EMI is primarily determined by equipment design, but how you wire and ground the
device is also critical to achieving EMI immunity. Therefore, it is important to select equipment
that has been designed and tested for industrial environments. The EMI standards for industrial
equipment include the EN61000-4-X series (IEC 1000-4-X and IEC8O1-X), EN55011 (CISPR11),
ANSI C62 and C63 and MIL-STD-461. Also, in industrial environments, you should use encoders
with differential driver outputs rather than single ended outputs, and digital inputs/outputs with
electrical isolation, such as those provided with optocouplers.
The EMI model provides only three options for eliminating the EMC problem:
• Reduce the EMI at the source.
• Increase the victim’s immunity to EMI (harden the victim).
• Reduce or eliminate the coupling mechanism.
In the case of servo drives, reducing the EMI source requires slowing power semiconductor
switching speeds. However, this adversely affects drive performance with respect to heat
dissipation and speed/torque regulation. Hardening the victim equipment may not be possible, or
practical. The final and often the most realistic solution is to reduce the coupling mechanism
between the source and victim. Filtering, shielding and grounding can achieve this.
Filtering
As mentioned above, high frequency energy can be coupled between circuits via radiation or
conduction. The AC power wiring is one of the most important paths for both types of coupling
mechanisms. The AC line can conduct noise into the drive from other devices, or it can conduct
noise directly from the drive into other devices. It can also act as an antenna and transmit or
receive radiated noise between the drive and other devices.
One method to improve the EMC characteristics of a drive is to use isolation AC power
transformer to feed the amplifier its input power. This minimizes inrush currents on power-up and
provides electrical isolation. In addition, it provides common mode filtering, although the effect is
limited in frequency by the interwinding capacitance. Use of a Faraday shield between the
windings can increase the common mode rejection bandwidth, (shield terminated to ground) or
provide differential mode shielding (shield terminated to the winding). In some cases an AC line
filter will not be required unless other sensitive circuits are powered off the same AC branch
circuit.
NOTE: “Common mode” noise is present on all conductors that are referenced to ground.
“Differential mode” noise is present on one conductor referenced to another conductor.
The use of properly matched AC line filters to reduce the conducted EMI emitting from the drive
is essential in most cases. This allows nearby equipment to operate undisturbed. The basic
operating principle is to minimize the high frequency power transfer through the filter. An effective
filter achieves this by using capacitors and inductors to mismatch the source impedance (AC line)
and the load impedance (drive) at high frequencies.
APPENDIX C: EUROPEAN UNION EMC DIRECTIVE
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