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Adjustable pot prohibited ?

 
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gilles.thesee(at)free.fr
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PostPosted: Fri Jan 25, 2019 7:42 pm    Post subject: Adjustable pot prohibited ? Reply with quote

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
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PostPosted: Sat Jan 26, 2019 6:16 am    Post subject: Adjustable pot prohibited ? Reply with quote

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
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PostPosted: Sat Jan 26, 2019 6:27 am    Post subject: Adjustable pot prohibited ? Reply with quote

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

My headsets use pots that are user accessible in flight.  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 ?

  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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bobnoffs



Joined: 04 Jul 2012
Posts: 83
Location: northern wi.

PostPosted: Sat Jan 26, 2019 7:03 am    Post subject: Adjustable pot prohibited ? Reply with quote

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.  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 ?

  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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gilles.thesee(at)free.fr
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PostPosted: Sat Jan 26, 2019 8:34 am    Post subject: Adjustable pot prohibited ? Reply with quote

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

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: 31
Location: Arvada, CO

PostPosted: Sat Jan 26, 2019 2:24 pm    Post subject: Re: Adjustable pot prohibited ? Reply with quote

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