SMA5005 & SMA5015 MANUAL
MANUAL # 5005-2040-000-F UPDATED: 6/1/2021
are sometimes neglected.
The primary objective of a high frequency ground system is to provide a well-defined path for HF
currents and to minimize the loop area of the HF current paths. It is also important to separate HF
grounds from sensitive circuit grounds. “Single Point Ground Types” shows single point grounds
for both series (daisy chain) and parallel (separate) connections. A single point, parallel connected
ground system is recommended.
A ground bus bar or plane should be used as the “single point” where circuits are grounded. This
will minimize common (ground) impedance noise coupling. The ground bus bar (GBB) should be
connected to the AC ground, and if necessary, to the enclosure. All circuits or subsystems should
be connected to the GBB by separate connections. These connections should be as short as
possible and straps should be used when possible. The motor ground conductor must return to the
ground terminal on the drive, not the GBB.
Shielding and Segregation
The EMI radiating from the drive enclosure drops off very quickly over distance. Mounting the drive
in an enclosure, such as an industrial cabinet, further reduces the radiated emissions. The cabinet
should have a high frequency ground and the size of the openings should be minimized. In
addition, the drive is considered an “open” device that does not provide the proper IP rating for the
environment in which it is installed. For this reason, the enclosure must provide the necessary
degree of protection. An IP rating or Nema rating (which is similar to IP) specifies the degree of
protection that an enclosure provides.
The primary propagation route for EMI emissions from a drive is through cabling. The cables
conduct the EMI to other devices, and can also radiate the EMI. For this reason, cable segregation
and shielding are important factors in reducing emissions. Cable shielding can also increase the
level of immunity for a drive.
For example:
•
Shield termination at both ends is extremely important. The common misconception that
shields should be terminated at only one end originates from audio applications with
frequencies <20 kHz. RF applications must be terminated with the shield at both ends, and
possibly at intermediate points for exceptionally long cables.
•
When shielded cables are not terminated at the cable connection and pass through the wall of
a cabinet, the shield must be bonded to the cabinet wall to prevent noise acquired inside the
cabinet from radiating outside the cabinet, and vice versa.
•
When shielded cables are terminated to connectors, the shield must be able to provide
complete 360
0
coverage and terminate through the connector backshell. The shield must
not
be grounded inside the connector through a drain wire. Grounding the shield inside the
connector couples the noise on the shield to the signal conductors sharing the connector and
virtually guarantees failure to meet European EMC requirements.
CIRCUIT
2
CIRCUIT
3
CIRCUIT
1
CIRCUIT
2
CIRCUIT
1
CIRCUIT
3
Figure 3-Single Point Ground Types
