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8 Tips for Minimizing or Eliminating EMI Noise

21 Jun 2012
Bob White

Noise, and I’m not talking about that terrible band you heard at the summer fest last year, but electromagnetic interference (EMI) noise. There are 8 key steps to consider when trying to eliminate EMI noise issues. If you follow these guidelines, you are much less likely to have problems with electrical noise in your application.

1. Use well designed cables: Good cable designs take in a number of key factors the address potential noise. The wire gauge, outer casing material, flex ratings, terminations, and shielding all play a role in minimizing noise issues. Our own experience shows customers who used the Kollmorgen designed cables have significantly fewer problems than those who built their own.

 

Feedback Cable Power Cable
Feedback Cable Power Cable

2. Use common-mode chokes on motor leads: Cables longer than 25 m (82 ft.) may need motor common-mode chokes. Check product documentation for details.

 

Choke
Common-mode Choke

 

3. Separate drive/motor power and signal cables: Bundle and route signal cables separately from motor and power cables. Run cables in separate conduits or maintain at least 100 mm (4 in.) between signal and power bundles for drives below 20 Amps. Use 150 mm (6 in) for 40 Amp drives and 200 mm (8 in) for 80 Amp drives.

If you are using a separate AC power filter, maintain separation of leads entering and exiting the line power filter. Locate the filter as close as possible to the point where the incoming power enters the cabinet. If you are using internal power filters, maintain at least 100 mm (4 in.) of separation between line power and motor leads. If it is necessary for input power and motor leads to cross, cross them at 90 degrees.

4. Splice cables properly: If you need to divide cables, use connectors with metal backshells. Ensure that both shells connect along the full 360 degrees of the shields. No portion of the cabling should be unshielded. Never divide a cable across a terminal strip.

5. Ensure good shield connections: For cables entering a cabinet, connect shields on all 360 degrees of the cable. Never connect a simple “pigtail.”

Shielding
Example of complete shield connection

6. Use differential inputs for analog signals: Noise susceptibility in analog signals is greatly reduced by using differential inputs. Normally, connect the output signal to the plus (+) differential input and the ground of the device generating the output to the minus (-) differential input. Use twisted-pair, shielded signal lines, and connecting shields on both ends. Many Kollmorgen drives provide internal filtering to reduce effects of electrical noise.

7. Ensure good connections between the cabinet components: Connect the back panel and cabinet door to the cabinet body using several conductive braids. Never rely on hinges or mounting bolts for ground connections. Provide an electrical connection across the entire back surface of the drive panel. Electrically-conductive panels such as aluminum or galvanized steel are preferred. For painted and other coated metal panels, remove all coating behind the drive.
8. Ensure good ground connection: Connect from cabinet to proper earth ground. Ground leads should be the same gauge as the leads to main power or one gauge smaller.


Following these 8 guidelines will ensure your installation will be free from EMI issues and noise will be minimized or eliminated.


What tips have you employed in your machine design to help minimize the effect of noise?

About the Author

Bob White

Bob White - Author
Bob has been with Kollmorgen for over 30 years, serving in a variety of positions including Applications Engineering, Product Marketing, Industry Marketing, Territory Management, Systems Engineering, Training, and now Digital Marketing. In addition to being published in several magazines over the years, Bob is also credited with the creation of a famous collegiate football tradition - The Sousaphone line dance to the Hokie Pokie - performed at every Virginia Tech Football game over the past 30 years! Connect with this author at Google+

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