MNALAZIN-02
22
Integration in the Servo System / Noise Suppression
Noise Suppression
While the above wiring and grounding practices should be sufficient to reduce noise and
interference issues to a minimum, in some systems sizing or other constraints do not allow
these guidelines to be put into use effectively. In these cases, the below items provide extra
means of noise suppression.
AC Line Filter
It is possible for noise generated by the machine to "leak" onto the main AC power, and then
get distributed to nearby equipment. If this equipment is sensitive, it may be adversely affected
by the noise. AC line filters can filter this noise and keep it from getting on the AC power signal.
The AC power filter should be mounted flat against the enclosure of the system using the
mounting lugs provided on the filter. Paint should be removed from the enclosure where the
filter is fitted to ensure effective metal to metal contact. The filter should be mounted as close to
the point where the AC power enters the enclosure as possible. Also, the AC power cable on the
load end of the filter should be routed as far from the AC power cable on the supply end of the
filter and all other cables and circuitry to minimize RF coupling.
Ferrite Suppression Cores
If PWM switching noise couples onto the encoder signals or onto the signal ground, then a
ferrite suppression core can be used to attenuate the noise. Take the motor leads and wrap
them around the suppression core as many times as reasonable possible, usually 2‐5 times.
Make sure to strip back the cable shield and only wrap the motor wires. There will be two
wires for single phased (brushed) motors and 3 wires for three phase (brushless) motors.
Wrap the motor wires together as a group around the suppression core and leave the motor
case ground wire out of the loop. The suppression core should be located as near to the drive
as possible.
Inductive Filter Cards
Inductive filter cards are added in series with the motor and are used to increase the load
inductance in order to meet the minimum load inductance requirement of the drive. They also
serve to counteract the effects of line capacitance found in long cable runs and in high voltage
systems. These filter cards also have the added benefit of reducing the amount of PWM noise
that couples onto the signal lines. This means they can be used in place of the suppression
cores mentioned above.
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