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shielded 5 wire for trim servo

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jessejenks(at)hotmail.com
Guest

Posted: Sun Jan 16, 2011 9:37 am Post subject: shielded 5 wire for trim servo

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
Guest

Posted: Mon Jan 17, 2011 6:43 am Post subject: shielded 5 wire for trim servo

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
Guest

Posted: Mon Jan 17, 2011 7:46 am Post subject: shielded 5 wire for trim servo

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
Guest

Posted: Mon Jan 17, 2011 7:55 am Post subject: shielded 5 wire for trim servo

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
Guest

Posted: Mon Jan 17, 2011 8:54 am Post subject: shielded 5 wire for trim servo

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
Guest

Posted: Mon Jan 17, 2011 9:04 am Post subject: shielded 5 wire for trim servo

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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