SMA5005 & SMA5015 MANUAL
MANUAL # 5005-2040-000-F UPDATED: 6/1/2021
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 an isolation AC power
transformer on the drive’s 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 inter-winding 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.
For drives brought for use in Europe, use of the correct filter is essential to meet emission
requirements. Detailed information on filters is included in the manual and transformers should be
used where specified in the manual.
AC Line Filter Selection
Selection of the proper filter is only the first step in reducing conducted emissions. Correct filter
installation is crucial to achieving both EMIL attenuation and to ensure safety. All of the following
guidelines should be met for effective filter use.
1) The filter should be mounted to a grounded conductive surface.
2) The filter must be mounted close to the drive-input terminals, particularly with higher frequency
missions (5-30 MHz). If the distance exceeds 600mm (2 feet), a strap should be used to
connect the drive and filter, rather than a wire.
3) The wires connecting the AC source to the filter should be shielded from, or at least separated
from the wires (or strap) that connects the drive to the filter. If the connections are not
segregated from each other, then the EMI on the drive side of the filter can couple over to the
source side of the filter, thereby reducing, or eliminating the filter effectiveness. The coupling
mechanism can be radiation, or stray capacitance between the wires. The best method of
