Today's Message Index:
----------------------
1. 04:45 AM - Re: Shielded wiring (FLYaDIVE)
2. 04:52 AM - Re: Shielded wiring (FLYaDIVE)
3. 05:12 AM - Re: Re: 3300 - low oil pressure at high RPM (FLYaDIVE)
4. 09:43 AM - Shielded wiring for P leads (Mark Hubelbank)
5. 11:30 AM - Re: Shielded wiring for P leads (BobsV35B@aol.com)
6. 03:25 PM - Re: Shielded wiring for P leads (Mark Hubelbank)
7. 08:54 PM - Re: 3300 - low oil pressure at high RPM (SteveR)
Message 1
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| Subject: | Re: Shielded wiring |
At what frequencies Noel?
What frequency are the spikes?
O! Wait a second... There ARE NO SPIKES on a SHIELD ... It is at
the same potential as GROUND!
Barry
On Mon, Sep 20, 2010 at 9:08 PM, Noel Loveys <noelloveys@yahoo.ca> wrote:
> noelloveys@yahoo.ca>
>
> Grounding at both ends turns the shielded wire into a capacitive inductor.
> Grounding at one end only, usually the end which is closest to the source
> of
> the power. Grounding at one end allows spikes and RFI to be sent to ground
> efficiently.
>
> Noel
>
> -----Original Message-----
> From: owner-jabiruengine-list-server@matronics.com
> [mailto:owner-jabiruengine-list-server@matronics.com] On Behalf Of AZFlyer
> Sent: September 19, 2010 4:51 PM
> To: jabiruengine-list@matronics.com
> Subject: JabiruEngine-List: Shielded wiring
>
>
> List,
>
> As I am major wiring challenged, I'm reading all the "experts" on getting
> my
> 3300 wired. There seems to be one school of thought on "Shielded wiring"
> that says..." ground both ends" and another school says only "ground the
> source end." or risk a Ground Loop (whatever that is?)
>
> source: Bingelis, Greg Richter, AeroElectric
>
> I haven't located that book " Wiring for Dummies" so, any help would be
> appreciated...
>
> Thanks,
> Mike
>
> --------
> Mike Miller @ millrml@aol.com
> 601 XL-B, 3300, Dynon
>
> Remember, "the second mouse gets the cheese"!
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=312943#312943
>
>
Message 2
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| Subject: | Re: Shielded wiring |
Very Good Points Noel.
On #4 - It does work BOTH ways.
On #5 -- Very Good Point Neil.... I failed to mention that. Thanks for
catching me. AND since we are in the EXPERIMENTAL CLASS - - - Radio Shack
(of which I despise) makes a very good filter, two of them mater of fact: A
Alternator filter and an inline filter. The cost use to be $15 each. CHEE
P
when you compare it against your travel time and build time.
And THANK YOU Noel.
I guess I am a bit like you too ... "not always" ;-)
Barry
On Mon, Sep 20, 2010 at 9:46 PM, Noel Loveys <noelloveys@yahoo.ca> wrote:
> #1 most important. To emphasize what Barry has written even if you take
> it off it may still look clean but may not be. So be sure to clean it
> vigorously. One thing though if you have to clean aluminium don=92t use
steel
> wool, aluminium oxide paper is safe to clean aluminium. Shards of steel
or
> iron will imbed itself into aluminium and cause corrosion in the aluminiu
m.
>
> #2 Full agreement if in doubt ground it out!
>
> #3 Again full agreement but the shielding is to protect from outside
> interference.
>
> #4 The only RF circuits that should be grounded at both ends are Coaxial
> connections. Of course coax is used almost entirely for RF transmissions
.
> Again the ground braid needs to be clean!
>
> #5 Again I=92m in total agreement with Barry but... Sometimes alternator
> squeal will penetrate the front end of your radios. In that case you wil
l
> need a choke on the input to the radio to filter out the squeal. A choke
is
> a circuit that comprises a capacitor and a coil of wire. The good news i
s
> they are readily available at auto parts shops.
>
>
> Not often I agree with *everything* a person says but this is really one
> of the exceptions that makes the rule... Well written Barry.
>
>
> Noel
>
> *From:* owner-jabiruengine-list-server@matronics.com [mailto:
> owner-jabiruengine-list-server@matronics.com] *On Behalf Of *FLYaDIVE
> *Sent:* September 19, 2010 9:17 PM
>
> *To:* jabiruengine-list@matronics.com
> *Subject:* Re: JabiruEngine-List: Shielded wiring
>
>
> Mike:
>
>
> Here are the RULES for Grounds and Shielding:
>
> 1 - GROUNDS - You can't inspect a ground by looking at it... YOU HAVE TO
> REMOVE IT... And while it is off clean CLEAN the contacts and replace the
> star washers..
>
> 2 - GROUNDS - The more the merrier. It took a LONG time but even Bob
> Nicholes FINALLY caught on and NOW SELLS multi ground point blocks. I us
e
> to frequent his web site/email list and pounded my case for about a year.
> But old wives tails die hard.
>
> 3 - GROUNDS - Ground Loops do NOT occur at DC. They are a High
> Frequency occurrence - High Frequency is in the RF Range (RF = Radio
> Frequency - Transmittable Frequencies)(Not Audio Frequencies... AF). AND
I
> still have a challenge out that NO ONE has met. MAKE ME A GROUND LOOP DC
> CIRCUIT!
>
> 4 - SHIELDING - Or in this case: What End of a Shield To Ground?
>
> RF circuits you shield at BOTH ENDS. And lets consider RF as only the
> frequencies we see in out planes... VHF.
>
> I know, I know, we all have GPS and they are at microwave frequencies.
> BUT! You are not building the units or the antennas, just installing th
em.
>
> 5 - SHIELDING - When you consider things such as Alternator Noise... The
> noise is in the audio frequency range and the source is the alternator so
> you ground at the source/alternator.
>
> NOW! What happens went the alternator wires reach the ACU/VR (Alternator
> Control Unit/Voltage Regulator) and then go out to other locations (ALT
> Switch)? Well there the rule stating says ground the source, but what is
> the source?
>
> The ACU/VR is the source, But it is already Grounded, usually to the
> firewall. SOooooo what do you do with the SHIELD?
>
> You play Electrical Engineer... Not on TV but on your plane. Start with
> grounding at the ACU/VR.
>
> But, think ahead and plan ahead. Make a Ground point at the ALT Switch a
nd
> put a ring lug on the shield. If you find ALT Noise try grounding at the
> ground point you made with the shield near (as close as possible) the ALT
> Switch.
>
>
> It is a GOOD idea to make Ring Lug Grounds on both ends of the shield jus
t
> in case the noise did not go to the same school as the electrons. YET!
In
> all honesty I have never found that to be the case.
>
>
> 6 - Don't forget to install a Capacitor on the OUTPUT of the Alternator B
+.
> All the shielding in the world won't do dittily if the noise is travelin
g
> out and down your B+.
>
>
> Barry
>
>
> On Sun, Sep 19, 2010 at 3:20 PM, AZFlyer <millrML@aol.com> wrote:
>
>
> List,
>
> As I am major wiring challenged, I'm reading all the "experts" on getting
> my 3300 wired. There seems to be one school of thought on "Shielded wiri
ng"
> that says..." ground both ends" and another school says only "ground the
> source end." or risk a Ground Loop (whatever that is?)
>
> source: Bingelis, Greg Richter, AeroElectric
>
> I haven't located that book " Wiring for Dummies" so, any help would be
> appreciated...
>
> Thanks,
> Mike
>
> --------
> Mike Miller @ millrml@aol.com
> 601 XL-B, 3300, Dynon
>
> Remember, "the second mouse gets the cheese"!
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=312943#312943
>
>
> ==========
> -List" target="_blank">
> http://www.matronics.com/Navigator?JabiruEngine-List
> ==========
> http://forums.matronics.com
> ==========
> le, List Admin.
> ="_blank">http://www.matronics.com/contribution
> ==========
>
>
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>
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>
> **
>
> **
>
> **
>
> **
>
> **
>
> **
>
> *http://www.matronics.com/Navigator?JabiruEngine-List*
>
> **
>
> **
>
> **
>
> *http://forums.matronics.com*
>
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Message 3
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| Subject: | Re: 3300 - low oil pressure at high RPM |
Roger:
Your statement - Is that true of all electrical oil pressure sending units?
I fly mostly Lycoming engines, NOT because I want to just because that is
what is on the planes. When I see LOW oil pressure or HIGH oil temps in
flight I do two things:
1 - Get my hart back under control.
2 - CROSSCHECK - Crosscheck Oil Temp against Oil Pressure and Oil Pressure
against Oil Temp.
If you have High Oil Temps AND Low Oil Pressure - YOU GOT A PROBLEM
If you have High Oil Temps and Normal Oil Pressure - You should expect to
see the Oil Temp come DOWN with the nose S&L and cruse power.
If you have Low Oil Temps and Normal Oil Pressure - You have a bad Gage -
More than likely
If you have Low Oil Pressure and Normal Oil Temps - You have a bad Gage -
More than likely
If you have High Oil Pressure and Normal Oil Temps - JUST SMILE - I like
that
On GA aircraft it has been the airframe manufacture that set the Oil
Pressure requirements on the gage. BIG FAA MISTAKE. Cessna wanted to
increase the Red Line on oil pressure from 100 PSI to 125 PSI... The FAA
would not let them do that. SOooooo what did Cessna do? They moved the oil
pressure pick up from the rear of the engine to the front AND increased the
Oil Pressure.. That increased the Oil Pressure through out the engine whill
STILL keeping the Gage Reading at 100 PSI Red Line :-) Smart Cookies!
Roger, is there REALLY a reason why you can't increase the Oil Pressure, 45
PSI sure sounds low? I'm learning your engines, I'm not too bad on Lycoming
- Rebuilt a few.
Barry
On Tue, Sep 21, 2010 at 1:31 AM, Roger Lee <ssadiver1@yahoo.com> wrote:
>
> The resistor type senders are very sensitive to partial grounds. We have
> the same issues on a FD CT. Fix the grounds to be more solid. Oil pressure
> senders are the first to show this because they are more sensitive than
> other instruments to poor grounds. Been there and done that on at least 15+
> planes.
>
> --------
> Roger Lee
> Tucson, Az.
> Light Sport Repairman - Maintenance Rated
> Rotax Repair Center
> 520-574-1080
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=313176#313176
>
>
Message 4
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| Subject: | Shielded wiring for P leads |
To all working with noise in aircraft wiring. I have been following
the listings on the subject of shielding and as a design engineer, I
have one thing to add (without the intent of generating any controversy).
This may help in cases where noise is comming from the ignition "P"
leads which run from the mags to the ignition key switch. There is a lot
of talk on grounding one end vers both ends of a shield. When one is
working with a RF situation, one needs to ground both ends otherwise the
shield will simple pick up the signal from the center conductor and act
as an antenna itself. After all an antenna at VHF frequencies is simply
a short wire connected at one end. In the case of the "P" leads, you may
be radiating RF energy picked up from the mags into the instrument panel
area, exactly where you really don't want it.
Thus when trying to prevent RF from "leaking" out, one needs to ground
the shield at both ends. This is more problematic in a composite
aircraft and other measures may be needed at the instrument panel end if
there is nothing to ground to. In those cases, some other RF tricks may
be required. I have not actually had to "de-noise" such an installation
but I would first try a combination of terminations (50 ohm carbon
resistor in series with 0.001 uf ceramic cap - very short leads from
shield to center conductor) and ferrite suppressors on the wire. Also
note that by using wire that has high loss at VHF some of the conducted
interference is attenuated. Typically non-coax shielded wire
(MIL-C-27500) is in this class.
Note that the connect shield at one end logic was originated to deal
with low frequency issues like ground loops. An even better solution in
some of those cases is to float the device at one end. For example for a
microphone lead, one can use insulating washers to separate the jack
from the airframe and then use the shield to provide the return path.
This is the best way to go when possible. All this is mentioned to
various degrees in the literature but I thought it does not hurt to give
the example.
--
Mark Hubelbank
NorthEast Monitoring
2 Clock Tower Place
Suite 555
Maynard, MA, 01754 - USA
mhubel@nemon.com
978-443-3955
Message 5
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| Subject: | Re: Shielded wiring for P leads |
Good Afternoon Mark,
What is your opinion of the practice of using the shield on the P lead
wiring as the ground path for the magneto switches and grounding the shield
only on the magneto end?
Happy Skies,
Old Bob
In a message dated 9/21/2010 11:43:34 A.M. Central Daylight Time,
mhubel@nemon.com writes:
To all working with noise in aircraft wiring. I have been following the
listings on the subject of shielding and as a design engineer, I have one
thing to add (without the intent of generating any controversy).
This may help in cases where noise is comming from the ignition "P" leads
which run from the mags to the ignition key switch. There is a lot of talk
on grounding one end vers both ends of a shield. When one is working with a
RF situation, one needs to ground both ends otherwise the shield will
simple pick up the signal from the center conductor and act as an antenna
itself. After all an antenna at VHF frequencies is simply a short wire connected
at one end. In the case of the "P" leads, you may be radiating RF energy
picked up from the mags into the instrument panel area, exactly where you
really don't want it.
Thus when trying to prevent RF from "leaking" out, one needs to ground the
shield at both ends. This is more problematic in a composite aircraft and
other measures may be needed at the instrument panel end if there is
nothing to ground to. In those cases, some other RF tricks may be required. I
have not actually had to "de-noise" such an installation but I would first try
a combination of terminations (50 ohm carbon resistor in series with 0.001
uf ceramic cap - very short leads from shield to center conductor) and
ferrite suppressors on the wire. Also note that by using wire that has high
loss at VHF some of the conducted interference is attenuated. Typically
non-coax shielded wire (MIL-C-27500) is in this class.
Note that the connect shield at one end logic was originated to deal with
low frequency issues like ground loops. An even better solution in some of
those cases is to float the device at one end. For example for a microphone
lead, one can use insulating washers to separate the jack from the
airframe and then use the shield to provide the return path. This is the best
way
to go when possible. All this is mentioned to various degrees in the
literature but I thought it does not hurt to give the example.
--
Mark Hubelbank
NorthEast Monitoring
2 Clock Tower Place
Suite 555
Maynard, MA, 01754 - USA
_mhubel@nemon.com_ (mailto:mhubel@nemon.com)
978-443-3955
Message 6
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| Subject: | Re: Shielded wiring for P leads |
Bob,
I believe this is the interesting case. Since in normal operation,
the switch is open, one has a piece of unterminated transmission line
running from the mag. If one assumes some VHF energy is injected into
the wire at the mag end (if not none of this matters), then at some
frequencies you have a transmission line which will have a high voltage
on the cabin end of the shield. That is effectively an antenna. To make
it worse, a lot of that antenna is in the cabin near your radios. How
bad this will be depends on the wire length. I have not done formal
tests on this but theory says that odd multiples of 1/4 wavelength
should be the worst length. At 127 MHz 1/4 wavelength in shielded wire
is about 0.39 M.
In an all metal plane, I would ground it at both ends. One can
still have some RF current flowing in the shield. To minimize that, one
could then terminate the line at the switch end with a series RC. This
will absorbe the RF component . I would expect the effect of this
terminator to be small.
Unfortunately, most engine noise is often from the high voltage
side of the ignition and none of this will help much. Then only
suppressor wire helps for unshielded ignition systems like the Jabiru
one. It further appears that the Jabiru system has the unfortunate
property that some RF energy is radiated from the mags themselves. This
part may be almost impossible to completely eliminate.
Nothing I am talking about has anything to do with things like
"alternator whine" which gets into earphone and microphone lines. That
is a whole different story.
On 09/21/2010 2:15 PM, BobsV35B@aol.com wrote:
> Good Afternoon Mark,
> What is your opinion of the practice of using the shield on the P lead
> wiring as the ground path for the magneto switches and grounding the
> shield only on the magneto end?
> Happy Skies,
> Old Bob
> In a message dated 9/21/2010 11:43:34 A.M. Central Daylight Time,
> mhubel@nemon.com writes:
>
> To all working with noise in aircraft wiring. I have been
> following the listings on the subject of shielding and as a design
> engineer, I have one thing to add (without the intent of
> generating any controversy).
>
> This may help in cases where noise is comming from the ignition
> "P" leads which run from the mags to the ignition key switch.
> There is a lot of talk on grounding one end vers both ends of a
> shield. When one is working with a RF situation, one needs to
> ground both ends otherwise the shield will simple pick up the
> signal from the center conductor and act as an antenna itself.
> After all an antenna at VHF frequencies is simply a short wire
> connected at one end. In the case of the "P" leads, you may be
> radiating RF energy picked up from the mags into the instrument
> panel area, exactly where you really don't want it.
>
> Thus when trying to prevent RF from "leaking" out, one needs to
> ground the shield at both ends. This is more problematic in a
> composite aircraft and other measures may be needed at the
> instrument panel end if there is nothing to ground to. In those
> cases, some other RF tricks may be required. I have not actually
> had to "de-noise" such an installation but I would first try a
> combination of terminations (50 ohm carbon resistor in series with
> 0.001 uf ceramic cap - very short leads from shield to center
> conductor) and ferrite suppressors on the wire. Also note that by
> using wire that has high loss at VHF some of the conducted
> interference is attenuated. Typically non-coax shielded wire
> (MIL-C-27500) is in this class.
>
> Note that the connect shield at one end logic was originated to
> deal with low frequency issues like ground loops. An even better
> solution in some of those cases is to float the device at one end.
> For example for a microphone lead, one can use insulating washers
> to separate the jack from the airframe and then use the shield to
> provide the return path. This is the best way to go when possible.
> All this is mentioned to various degrees in the literature but I
> thought it does not hurt to give the example.
>
> --
> Mark Hubelbank
> NorthEast Monitoring
> 2 Clock Tower Place
> Suite 555
> Maynard, MA, 01754 - USA
> mhubel@nemon.com
> 978-443-3955
>
> *
>
>
> *
--
Mark Hubelbank
NorthEast Monitoring
2 Clock Tower Place
Suite 555
Maynard, MA, 01754 - USA
mhubel@nemon.com
978-443-3955
Message 7
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| Subject: | Re: 3300 - low oil pressure at high RPM |
Rob,
According to my friend, it was actually below the green at high RPM (indicating
30psi, low redline is 32psi). The warning light on the panel illuminated, so
I think it is probably lower than it should be. The gauge is an EIS, maybe the
model 4000. My first guess was a bad ground. Is this gauge a resistor type?
I assume so, being electronic.
My primary question is should a Jabiru exhibit such a large oil pressure drop when
RPM is increased (from 45+psi down to 30psi)? Is that typical? If not, there
is some type of problem, even if it is just instrumentation.
Thanks for the help so far!
Steve Ruse
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=313326#313326
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