Curtis:
For the testing of Military systems, I always look for the worst possible, yet
normal mode of operation. Sometimes a power supply will be noisier at little
load than at high load, so we usually test it at 10%, 50% and 100% loading.
Electromechanical devices are operated as close to normal as possible, so that
means that actuators driving flight control surfaces are loaded (with weights
and/or elastomeric springs) to simulate flight loads. If I had a motor which
drove a pump or blower or whatever, I would operate it at its normal speed and
torque loading. If the loading was unpredictable, I would do a quick analysis
of emissions to determine the worst-case operating point, and then do the rest
of my emission testing in that condition.
Predicting the worst-case operating condition for susceptibility (immunity)
testing is a lot more difficult. If I didn't have a good engineering analysis
of the EUT to help me, I would probably use the same operating condition that
I used for the emission tests.
Ed Price
ed.pr...@cubic.com <blocked::mailto:ed.pr...@cubic.com> WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (FAX)
Military & Avionics EMC Is Our Specialty
________________________________
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Bender,
Curtis
Sent: Thursday, October 30, 2008 8:56 AM
To: emc-p...@ieee.org
Subject: unloaded motors - EMC testing
Greetings IEEE EMC-PSTC forum members and experts.
I am looking to answer some questions concerning the EMC testing of
portable
commercial and industrial equipment; specifically the testing of motors at
“no load”.
I have my own “opinions” and experience concerning these questions but I
would like to get some factual data (standard reference) and documented EMC
standard design philosophy if at all possible. I was hoping the IEC guide 107
would have noted this design philosophy but unless I missed it I did not see
it.
1. Can someone explain how and why “no load” frequently occurs in
EMC
test standards? See CISPR 14-1 section 7.3 for example.
2. Why is “no load” used and why isn’t a loaded or partially loaded
motor used? (other than “testing for all possible working conditions is not
practical for technical and economic reasons”). Is this representative of
“real world” conditions? If not how is it correlated to the “real
world?”
3. Typically do the limits included in EMC standards correspond
(or are
reduced) to the actual application? How is this correlated to “real world”
applications? Or is this covered in statements such as: “the limits given in
this standard take into account uncertainties” (from CISPR 12)?
As always, I look forward to your comments.
Regards,
Curt
______________________________________________________
Curtis Bender | T: 616.994.4221| F: 616.994.4127
Global Technical Approvals/Lead Project Engineer
Tennant Company | Creating a cleaner, safer world for 135 years.
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