nuckolls.bob(at)aeroelect
Guest
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 Posted: Tue May 19, 2009 8:00 am Post subject: EV200 noise |
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At 03:33 AM 5/19/2009, you wrote:
| Quote: | Bob,
Why would the Tyco EV200 create noise in some applications and how
could this problem be mitigated?
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"Noise" by definition is the artifact of rapidly
changing current flow that propagates from some
antagonist to some victim. This is described in
more detail in the book. Sometimes the 'noise'
is an intentional byproduct of a useful radiation.
For example, you radiate strong signals from your
comm and transponder antennas to achieve
a useful purpose. In some cases, the stronger the
radiation, the better. However, this radio frequency
energy can become a nuisance too. Its sorta like
being pleased that your wheat fields are benefiting
from a good rain shower but the holes in your roof
are a source of concern.
The EV200 (and similar devices) use an transistor
that's turned on with varying duty cycle to reduce
current in the contactor coil after pull-in is
achieved. The speed of the switching device, the
amount of current it carries, the area of its
"antennas", the frequency of operation and the
artifacts of current modulation flowing out on
the wires are all ingredients that go into
a recipe for problems.
The stuff that gets outside the product needs
to be evaluated for potential nuisance if not
hazard. This is part of what DO-160/Mil-STD-704
is about. In the case of the EV200, the occasional
OBAM aircraft builder has heard the duty cycle
switching of the EV200's control electronics as
a "buzz" in their audio system.
I've not been able to put my hands on one of these
problems to deduce the magnitude of potential noise
or track down the specific propagation path. However,
it's a pretty fair bet that poor grounding techniques
are the probable cause.
I wouldn't shy away from an EV200 installation
based on a reported noise issue. I've never found
a noise problem I couldn't fix. I've found problems
that the customer decided not to fix because it
involved $millions$ of design changes to an
airframe. But in our airplanes, the risk of noise
is low, the cost of the solution is not great.
In response to our List discussion late last week
on the ratings for the lowly el-cheeso contactors,
I've begun a design for a contactor power management
module. This device will be assembled much like the
over voltage modules . . . quasi-potted in double
walled heat shrink. It's easy to add this device
to an el-cheeso contactor and achieve improved
electrical performance that emulates the EV200.
At the same time, it separates control electronics
from the contactor. If the contactor ever requires
replacing, then you don't need to buy new electronics.
Similarly, if the electronics craps, you don't toss
out a perfectly good contactor. See:
http://www.aeroelectric.com/Catalog/AEC/9024/9024-700-1P1.pdf
I have an upcoming opportunity to get into the EMC
lab with a customer's product for DO-160 conducted
emissions testing. I'm planning to piggy-back a
couple of my projects into the same testing session.
If my software guru can get me some exemplar chips
for the 9024, I can do an EMC look-see to confirm
my confidence in its OBAM aircraft friendly demeanor.
This module will drastically reduce the temperature
rise on the RBM/W-R/Stancore contactors. This not only
reduces energy required to keep the critter closed,
it honors the manufacturer's ratings limits for
use in systems with bus voltages high enough to
charge batteries.
Bob . . .
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