Today's Message Index:
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1. 05:44 AM - Re: Re: Pitot Heat Ground (Robert L. Nuckolls, III)
2. 06:05 AM - Re: Pitot Heat Ground (Robert L. Nuckolls, III)
3. 06:59 AM - Re: Pitot Heat Ground (Gerry Van Dyk)
4. 08:37 AM - Re: Pitot Heat Ground (Robert L. Nuckolls, III)
5. 08:44 AM - Re: Pitot Heat Ground (Robert L. Nuckolls, III)
6. 02:04 PM - Re: Pitot Heat Ground (Robert L. Nuckolls, III)
7. 04:52 PM - Re: Pitot Heat Ground (Gerald Champagne)
Message 1
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Subject: | Re: Pitot Heat Ground |
>
>But I'd hope someone at Dynon could give you the real answer.
Agreed. I've had some conversation with Dynon
in years past . . . conversations that gave
the impression of solid technical competence.
Given their successes in this market, your
expectations for the quality of their support
is not unwarranted.
>If the magnetometer is built into the ADAHRS,
>you could just prepare for having to remote it
>(a few extra wires), and just try it before purchasing the extra
magnetometer.
>
>On Tue, Sep 8, 2015 at 5:37 PM, JDA_BTR
><<mailto:dudley@jdatkinson.net>dudley@jdatkinson.net> wrote:
>"JDA_BTR" <<mailto:dudley@jdatkinson.net>dudley@jdatkinson.net>
>
>It's a good thought.=C2 The ADAHRS location in
>the wing is very convenient to the pitot for
>AOA.=C2 The magnetometer can be had as a remote unit and put elsewhere.
>
>Nonetheless I would like to know about the
>situation as presented, because I'm curious -
>why would the controller box be grounded if it
>is so important to carry a ground wire all the
>way back to the battery; and when the faqs here
>say the ground can be local and simple.=C2 Would
>running that wire reduce magnetometer interference even if I ran it?
Exactly, that "ground wire directly to the
battery" phrase has popped up over the
years in several OBAM aviation installation
manuals . . . were anyone at King Radio, Collins,
Narco or ARC to make such an assertion, the
writer should be tasked with a "lunchtime
learning session" for colleagues and instructed
to "bring us up to date on the physics of
your assertion." I would LOVE to be in
the audience for THAT one!
I'm not clear as to where the all the
components are located on the airplane
with respect to each other . . . pitot
tubes are generally on the wing, the AHRS
is out there too? Help me understand . . .
Bob . . .
Message 2
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Subject: | Re: Pitot Heat Ground |
At 01:50 PM 9/9/2015, you wrote:
>I don't see anything in the dynon installation manual about
>connecting directly to the battery.
><http://dynonavionics.com/downloads/Install_Guides/Heated_Unheated_AOA_Pitot_Probe_Installation_Guide_-_Rev_C.pdf`>http://dynonavionics.com/downloads/Install_Guides/Heated_Unheated_AOA_Pitot_Probe_Installation_Guide_-_Rev_C.pdf`
>It says:
>
>Do not connect the Black (Ground) wire to the airframe as a Ground
>connection. Doing so will introduce high currents (10A) into the
>airframe. This can introduce a significant voltage drop, and
>potentially cause engine instrumentation, avionics, and audio system
>electrical problems.
Good find . . . the author of these words demonstrates
a poor understanding of grounding for the purposes
of achieving (1) reliable power to the device and (2)
minimizing risk of noise propagation to other
systems.
>Also it says the ground wire should be:
>Constant connection to ground (not routed through a switch or fuse /
>circuit breaker). Must be sized to conduct 10A with minimal voltage
>drop. Ground connection must be constant FOR PITOT HEAT STATUS LINE
>(White wire) to operate when the controller is powered Off or not functioning.
Just why anyone would run a ground wire through a
switch is a mystery . . .
It's sad to discover these kinds of muddy thought
in the manuals for what should be a no-brainer
installation. Those kinds of statement inject what I
have dubbed a "divide by zero" factor into
the document.
Emacs!
Whether you're a politician, engineer, philosopher, CEO
. . . what ever. Validity of many hours/pages of ideas become
suspect when you include the "divide by zero" assertion
into your 'formula for success'.
Such assertions will at best make the rest of your
ideas suspect . . . if not nullify them entirely.
It's sort like spending an hour on the phone with tech
support before somebody notices that the thing isn't
even plugged in . . .
I used to have a contact in Dynon management . . . haven't
talked in years. I'll see if he's even still there . . .
Bob . . .
Message 3
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Subject: | Re: Pitot Heat Ground |
Bob=2C perhaps I=27m misunderstanding this thread=2E You said=3A
=3E
=3E
=3E
=3E Just why anyone would run a ground wire through a
=3E switch is a mystery =2E =2E =2E-
=3E
=3E It=27s sad to discover these kinds of muddy thoughts
=3E in the manuals for what should be a no-brainer
=3E installation=2E
=3E
=3E
=3E
The quote from the installation manual is=3A
=3E
=3E
=3E
=3E
=3E =3E Constant connection to ground (NOT routed through a switch or fu
se / circuit breaker)=2E
=3E
=3E
=3E
=3E
Isn=27t the manual telling the installer to bring the ground wire back t
o the main ground block=2C presumably the forest-of-tabs on the firewall
=3F Why would this manual be cause for concern=3F
Gerry
Message 4
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Subject: | Re: Pitot Heat Ground |
>>>Constant connection to ground (NOT routed through a switch or fuse
>>>/ circuit breaker).
>Isn't the manual telling the installer to bring the ground wire back
>to the main ground block, presumably the forest-of-tabs on the
>firewall? Why would this manual be cause for concern?
Why would such a statement even be necessary?
Are there cases in the wild where someone's
on-purpose design did take ground through a fuse
or switch? The mere mention this would probably
bring smiles to the system integrators at
Textron but it plant's seeds of an exceedingly
poor idea in the minds of their target
market . . . the neophyte builder/installer.
"Gee, are there instances where ground paths
SHOULD go through switches or breakers?"
This is why I have always encouraged folks
to supply lucid wiring schematics with their
products. No pictograms. Schematics are
to electronics as numbers and operator
symbols to mathematicians. The universal
language understanding of how best to assemble
something is the annotated schematic . . .
like those you see in Appendix Z of the
book, diagrams at the back of a Cesnna
Service Manual, or the EXCELLENT diagrams
published for KIA cars. Those diagrams offer
a path for understanding between designers and
users. I once spent a couple weeks in CA
giving Japanese technicians an overview of
a television time base corrector that my
company built . . . and I wrote the manual
for. Their English was poor, my Japanese nil,
but they understood television, waveforms
and SCHEMATICS.
If an idea can be easily depicted on the
wiring diagram, then do it. This completely
negates the need for words. If words ARE
offered, they should re-enforce the schematic
with very low risk for doubt.
Words are 'icing' on a an underlying
'cake' that should stand alone on the
language of universal symbology and
mathematical expression.
I would hope the author of the ground wire
statement was simply trying to compensate
for the lack of lucid illustrations. As
we've seen in this thread, vagaries in
the use and understanding of language have
generated a whole lot of conversation trying
to figure out what COULD have been described
in a few lines on a page. Unfortunately,
other words in the document do not suggest
that the author has a good handle on how
the various appliances on an airplane can
be encouraged to happily co-exist.
This may well be an example of a condition
common to many tech manufacturers. Marketing
hands down goals, engineering designs to
the goals, production experts package and
manufacture the thing and 'tech writers'
put out the books. It's the Silo-Syndrome
where good stuff can get blown to the winds
as a task is pitched from one silo to the next.
Bob . . .
Message 5
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Subject: | Re: Pitot Heat Ground |
At 04:55 PM 9/8/2015, you wrote:
>Subject: AeroElectric-List: Pitot Heat Ground
>From: "JDA_BTR" <dudley@jdatkinson.net>
>To: aeroelectric-list@matronics.com
>
>
>I read the faqs, and know the recommendation to just take the pitot
>ground to the chassis.
Let's see if we can zero in on the physics. Is
The pitot heat controller in conductive enclosure?
Does its ground wire make electrical connection
to the enclosure?
If the above are both 'yes' then run the power
ground to a point on the airframe separate from
but in the vicinity of where the controller
lives in the airplane.
Adding a 'ground wire' off to some other
portion of the airplane is of no value. It
will simply be a conductor of much higher
resistance than the airframe and carry a
exceedingly small proportion of pitot heater
current.
Bob . . .
Message 6
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Subject: | Re: Pitot Heat Ground |
Another 'point of physics' that goes to your
question. I just went to the workbench, laid
my handy military surplus compass on the bench
then held a wire over the needle at the optimal
angle to antagonize the readings.
With 3A flowing in the wire, I had to lower
it to within about 5 inches to detect any
movement of the needle. 10A would probably
produce noticed motion at 14 inches or so.
The interference I noted was 1 degree or
less. The most rigorous certification of
hardware under DO160 for magnetic effects
is 'category Z' which may produce 1 degree
of deflection while located 0.3 meters away
from the compass . . . or about 12 inches.
My 'shade tree' magnetic effects experiment
suggests that 12' of separation for a 10A
conductor will produce no observable deflections
from real magnetic heading.
Bob . . .
Message 7
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Subject: | Re: Pitot Heat Ground |
On Thu, Sep 10, 2015 at 4:02 PM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
>
> With 3A flowing in the wire, I had to lower
> it to within about 5 inches to detect any
> movement of the needle. 10A would probably
> produce noticed motion at 14 inches or so.
>
That doesn't sound right. The strength of a magnetic field should increase
linearly with current, but should fall off as a function of distance
cubed. A 3A current at 5 inches should show the same deflection as a 10A
current at about 7.5 inches, not 14 inches. Did I miss something?
Gerald
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