________________________________
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of
pat.law...@slpower.com
Sent: Thursday, November 13, 2008 9:43 AM
To: emc-p...@ieee.org
Subject: Test setup for equipment operated intermittently
Hi,
I need to run EMC tests on a piece of high-power medical equipment that
is
used on an intermittent basis. The run time is about 15 seconds to 2 minutes
on-time, followed by about 10 minutes off-time. This is comparable to typical
system usage. This causes problems with EMC testing, since you normally need
a longer observation period.
1) The equipment could be operated continuously, but extra cooling
would have
to added to the test setup, which is not part of a typical system. In the
spirit of regulatory intent would this be considered overtesting?
2) Could testing be done at the highest power level that allows
continuous
operation?
What load conditions/test setup are appropriate for an application like
this?
Pat Lawler
EMC Engineer
SL Power Electronics Corp.
Pat:
I think you can do most anything that doesn't significantly affect the
radiation pattern of the EUT, from a big fan over in the corner of the test
chamber to more exotic things. I frequently have to test military systems that
have similar duty cycle restrictions. One trick I use is to route shop
compressed air, through plastic lines, onto critical components. If I need
even more cooling, I have used CO2 in place of air. Once, maybe as more of an
experiment than anything else, I used compressed air to drive a vortex tube (a
passive gadget that splits the compressed air in a pair of air flows, one hot
and one cold), yielding a modest flow of about -40C cooling air.
You should also consider if the medical device is always used at a single
output setting, or does it allow for a range of exposures? Sometimes, the
predominant noise is a function of power supply loading, and it doesn't always
follow that maximum device output equals maximum noise output. If I encounter
a range of operation, I usually do a quick test at 10% / 50% / 90% output
power to see if noise predominates toward one extreme or another.
Regards,
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
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