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Adjustable pot prohibited ?

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gilles.thesee(at)free.fr
Guest

Posted: Fri Jan 25, 2019 7:42 pm Post subject: Adjustable pot prohibited ?

Hello all,



In the past few months I designed for some building buddies a small 

electronic device to close a relay when below a certain voltage.

It includes a small multi turn potentiometer to adjust the 13.5 V or 

else set point. The device is currently under test.



My intention was, once satisfied with the operation, to seal the 

potentiometer with a dab of varnish.



But a friend just tells me that in aviation adjustable pots are 

prohibited, and that once adjusted, we should normally replace the 

potentiometer with fixed resistors or adequate value.

Does anyone have further information about this rule ?



Thanks,



-- 

Best regards,

Gilles

http://contrails.free.fr

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 26, 2019 6:16 am Post subject: Adjustable pot prohibited ?

At 09:40 PM 1/25/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: GTH <gilles.thesee(at)free.fr>



 Hello all,



 In the past few months I designed for some building buddies a small electronic device to close a relay when below a certain voltage.

 It includes a small multi turn potentiometer to adjust the 13.5 V or else set point. The device is currently under test.



 My intention was, once satisfied with the operation, to seal the potentiometer with a dab of varnish.



 But a friend just tells me that in aviation adjustable pots are prohibited, and that once adjusted, we should normally replace the potentiometer with fixed resistors or adequate value.

 Does anyone have further information about this rule ? 	


   Never heard of it.



   An off-the-shelf piece of avionics for

   TC aircraft is subjected to a constellation

   of environmental and performance qualification

   tests.



   Adjustable pots are becoming rare . . . they

   live in an analog world rapidly being over

   taken by digital . . . but there are hundreds

   of pot styles that 'stay put' under

   expected stresses. Hence, offer no concerns

   for un-expected re-adjustment.



 

 

   Bob . . .

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sportav8r(at)gmail.com
Guest

Posted: Sat Jan 26, 2019 6:27 am Post subject: Adjustable pot prohibited ?

Maybe it's a general prohibition on smuggling via aircraft?



My headsets use pots that are user accessible in flight.Â  Scary.

On Sat, Jan 26, 2019 at 9:20 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 09:40 PM 1/25/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: GTH <gilles.thesee(at)free.fr (gilles.thesee(at)free.fr)>



 Hello all,



 In the past few months I designed for some building buddies a small electronic device to close a relay when below a certain voltage.

 It includes a small multi turn potentiometer to adjust the 13.5 V or else set point. The device is currently under test.



 My intention was, once satisfied with the operation, to seal the potentiometer with a dab of varnish.



 But a friend just tells me that in aviation adjustable pots are prohibited, and that once adjusted, we should normally replace the potentiometer with fixed resistors or adequate value.

 Does anyone have further information about this rule ? 	


 Â  Never heard of it.



 Â  An off-the-shelf piece of avionics for

 Â  TC aircraft is subjected to a constellation

 Â  of environmental and performance qualification

 Â  tests.



 Â  Adjustable pots are becoming rare . . . they

 Â  live in an analog world rapidly being over

 Â  taken by digital . . . but there are hundreds

 Â  of pot styles that 'stay put' under

 Â  expected stresses. Hence, offer no concerns

 Â  for un-expected re-adjustment.



 

 

 Â  Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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bobnoffs

Joined: 04 Jul 2012
Posts: 132
Location: northern wi.

Posted: Sat Jan 26, 2019 7:03 am Post subject: Adjustable pot prohibited ?

one hit or two? sorry, couldn't resist.



On Sat, Jan 26, 2019 at 8:31 AM Bill Boyd <sportav8r(at)gmail.com (sportav8r(at)gmail.com)> wrote:



 	  Quote: 	
		  Maybe it's a general prohibition on smuggling via aircraft?



My headsets use pots that are user accessible in flight.Â  Scary.

On Sat, Jan 26, 2019 at 9:20 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 09:40 PM 1/25/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: GTH <gilles.thesee(at)free.fr (gilles.thesee(at)free.fr)>



 Hello all,



 In the past few months I designed for some building buddies a small electronic device to close a relay when below a certain voltage.

 It includes a small multi turn potentiometer to adjust the 13.5 V or else set point. The device is currently under test.



 My intention was, once satisfied with the operation, to seal the potentiometer with a dab of varnish.



 But a friend just tells me that in aviation adjustable pots are prohibited, and that once adjusted, we should normally replace the potentiometer with fixed resistors or adequate value.

 Does anyone have further information about this rule ? 	


 Â  Never heard of it.



 Â  An off-the-shelf piece of avionics for

 Â  TC aircraft is subjected to a constellation

 Â  of environmental and performance qualification

 Â  tests.



 Â  Adjustable pots are becoming rare . . . they

 Â  live in an analog world rapidly being over

 Â  taken by digital . . . but there are hundreds

 Â  of pot styles that 'stay put' under

 Â  expected stresses. Hence, offer no concerns

 Â  for un-expected re-adjustment.



 

 

 Â  Bob . . .

- The Matronics AeroElectric-List Email Forum -

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gilles.thesee(at)free.fr
Guest

Posted: Sat Jan 26, 2019 8:34 am Post subject: Adjustable pot prohibited ?

Le 26/01/2019 à           15:16, Robert L. Nuckolls, III a écrit :

         

      	  Quote: 	
		                           

             Never heard of it.

           

                       [...]     there are hundreds

             of pot styles that 'stay put' under

             expected stresses. Hence, offer no concerns

             for un-expected re-adjustment.

         	
     

     Thank you sir !

     So I'll stick to my trimmer and varnish.

     -- 

       Best regards,

       Gilles

       http://contrails.free.fr

       http://lapierre.skunkworks.free.fr

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jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Sat Jan 26, 2019 2:24 pm Post subject: Re: Adjustable pot prohibited ?

FWIW, I had an older certified Alcor combination EGT/CHT gauge that used adjustable pots. It eventually started to have intermittent problems on the CHT side.  The culprit was the little adjustable pot, and I replaced it with a precision resistor.  This was on my first homebuilt that I flew for 28 years.

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_________________
John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

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