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shielded 5 wire for trim servo

 
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jessejenks(at)hotmail.com
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PostPosted: Sun Jan 16, 2011 9:37 am    Post subject: shielded 5 wire for trim servo Reply with quote

I'm wiring my elevator trim servo and wondering what to do with the shield on the 5 wire cable that came with my kit. The Ray Allen instructions say nothing about it. Should I ground it at one or both ends, or just ignore it?
Thanks.
Jesse
[quote][b]


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Jan 17, 2011 6:43 am    Post subject: shielded 5 wire for trim servo Reply with quote

At 11:28 AM 1/16/2011, you wrote:
Quote:
I'm wiring my elevator trim servo and wondering what to do with the
shield on the 5 wire cable that came with my kit. The Ray Allen
instructions say nothing about it. Should I ground it at one or both
ends, or just ignore it?
Thanks.
Jesse

Your choice. There is no value for having these
wires shielded so what you do with the shield
is optional and of no electrical significance.

Bob . . .


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etienne.phillips(at)gmail
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PostPosted: Mon Jan 17, 2011 7:46 am    Post subject: shielded 5 wire for trim servo Reply with quote

Hi Bob

Thinking aloud here...

Wouldn't the noisy current of a brushed DC motor emit a heap of RF over long wire runs (especially if the trim servo is locally grounded)?

Would that not be the reason for the shielding on the cable - not to stop the servo from being interfered with, but to reduce the emitted noise?

Thanks
Etienne

On 17 January 2011 16:40, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

At 11:28 AM 1/16/2011, you wrote:
Quote:
I'm wiring my elevator trim servo and wondering what to do with the shield on the 5 wire cable that came with my kit. The Ray Allen instructions say nothing about it. Should I ground it at one or both ends, or just ignore it?
Thanks.
Jesse


  Your choice. There is no value for having these
  wires shielded so what you do with the shield
  is optional and of no electrical significance.

  Bob . . .

[b]


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jessejenks(at)hotmail.com
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PostPosted: Mon Jan 17, 2011 7:55 am    Post subject: shielded 5 wire for trim servo Reply with quote

Thanks Bob,
In digging around on the Vans forum I saw mention that the Ray Allen trim indicator could go bonkers while transmitting on a radio if the wire wasn't shielded. I'm going to attempt to use the trim indicator on my Dynon screen so hopefully it won't be a problem, but I soldered a 22 gauge wire onto the shield at the servo end so I can run it into the fuselage just in case.

Quote:
Date: Mon, 17 Jan 2011 08:40:15 -0600
To: aeroelectric-list(at)matronics.com
From: nuckolls.bob(at)aeroelectric.com
Subject: Re: shielded 5 wire for trim servo

--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

At 11:28 AM 1/16/2011, you wrote:
>I'm wiring my elevator trim servo and wondering what to do with the
>shield on the 5 wire cable that came with my kit. The Ray Allen
>instructions say nothing about it. Should I ground it at one or both
>ends, or just ignore it?
>Thanks.
>Jesse

Your choice. There is no value for having these
wires shielded so what you do with the shield
is optional and of no electrical significance.
&gt=====================

[quote] _====



Quote:
[b]


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Jan 17, 2011 8:54 am    Post subject: shielded 5 wire for trim servo Reply with quote

At 09:53 AM 1/17/2011, you wrote:
Quote:
Thanks Bob,
In digging around on the Vans forum I saw mention that the Ray Allen
trim indicator could go bonkers while transmitting on a radio if the
wire wasn't shielded. I'm going to attempt to use the trim indicator
on my Dynon screen so hopefully it won't be a problem, but I
soldered a 22 gauge wire onto the shield at the servo end so I can
run it into the fuselage just in case.

If that's the case, then the problem is in the indicator,
not the wiring. DO-160 qualification protocols for accessories
in TC aircraft do not generally allow a latent design
deficiency to be masked by user installed shielding,
filters, relocation, etc.

If you're wiring the actuator's potentiometer leads
to the inputs of some indicator OTHER than a Ray-Allen
product, then you've got a whole new ball game.

If you DO need the shielding, it should be connected
to ground as close as practical to the victim. I.e.
the indicator. Take the pigtail to a ground pin in
the connector.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Jan 17, 2011 9:04 am    Post subject: shielded 5 wire for trim servo Reply with quote

At 09:42 AM 1/17/2011, you wrote:
Quote:
Hi Bob

Thinking aloud here...

Wouldn't the noisy current of a brushed DC motor emit a heap of RF
over long wire runs (especially if the trim servo is locally grounded)?

Given that the actuator is a PM motor device with both
lead wires floating (to achieve CW/CCW operations) then
there's no 'local grounding' opportunities to be considered.
So all 5 wires from the actuator should be brought forward
with the motor pair splitting out to the trim command controls
and 3 position-pot wires going to the selected indicator.

Brushed DC motors DO emit noise. But it's a matter of
degree combined with the manner in which the noise
gets out of the system (radiated, conducted or both).
In this case, that tiny little motor (draws about 100 mA
as I recall) is a mouse roaring in a cacophony of
other noises. Further, the noise will come out conducted
on the twisted pair . . . these cannot radiate nor can
they become victims of radiation with respect to the
motor noise.

Quote:
Would that not be the reason for the shielding on the cable - not to
stop the servo from being interfered with, but to reduce the emitted noise?

The actuator itself contains a motor and a pot. These
are not potential victims. The motor does generate
a modicum of insignificant noise. The pot generates
no noise.

If the Ray-Allen indicators have proven susceptible
to RF, it will be shown to have root cause in a common
mode conduction of RF into the indicator circuitry.
This MIGHT be improved upon by shielding, the common
wisdom seems to indicate this is the case. But it's
like carrying a fire extinguisher to offset the potential
effects of known fuel leaks. Better to fix the 'leak'
inside the indicator.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================


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