From: <flyrotary@lancaironline.net>
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Full-name: ARGOLDMAN
Message-ID: <19d3c6.5d7fe5.43358e82@aol.com>
Date: Thu, 24 Sep 2015 13:36:02 -0400
Subject: Re: [FlyRotary] Re: OT: Calibrating altimeter and alt encoder
To: flyrotary@lancaironline.net
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Ya,
 
don't forget that the METAR suggested setting may be quite old and the  
reading not necessarily at your airport.
 
The best way to set the Dynon, or any other altimeter is to use a  
manometer. There are many tables that say what altitude is equivalent to what  
column of water (or mercury)..
 
Easier to have a shop look at it and calibrate it.
 
Rich
 
 
In a message dated 9/24/2015 11:42:18 A.M. Central Daylight Time,  
flyrotary@lancaironline.net writes:

On 9/24/2015 11:12 AM, ARGOLDMAN wrote:


Not sure that I understand completely, however the encoded altitude has  
nothing to do with your local setting.

Yep. I set the Dynon to 29.92. Then the displayed  altitude should match 
what the encoder sends out.

Problem is how to  accurately (preferably to within 10 feet) calibrate the 
Dynon. Obviously using  nearby METAR reported pressures was not successful. 
And I'm beginning to think  that the instruments that reports pressure to 
METARs may not be all that  accurate -- varies from airport to airport.


all encoders are calibrated to the same calibrations so that when ATC  or 
whoever reads the reply all of the aircraft that they are looking at have  
the same altitude bias independent of errors in setting the kollsman window  
in the various aircraft.
 
Since you have gone into the encoder, there is a possibility that the  
alterations that you have done may yield a constant error for ATC which is  
worse than not having an altitude report at all. You might want to have your  
encoder checked with proper instruments.
 
Something that comes to mind is that since the encoder and the  altimeter 
are both run from the static source, that there is a blockage,  kink, water 
etc that may be influencing the readings.
 
Good luck in your quest for vertical reading stability
 
Rich
 
 
In a message dated 9/24/2015 8:58:23 A.M. Central Daylight Time, 
_flyrotary@lancaironline.net_ (mailto:flyrotary@lancaironline.net)   writes:

Off  topic, except it's in a 13B Van's RV-3 ;-)

Again, after flying home  from Sun'n'Fun, ATC saw me several hundred feet 
below what I saw on my  altimeter.

Last week I finally got around to removing all the  screws that holds the 
fuselage top over the instruments.

I  hooked LEDs across the data lines that run from the altitude encoder  
to the transponder (gray code).
(note that 1 is actually 0 volts --  active low).

I checked METARs at nearby airports -- CTY, GNV... and  I know my 
elevation exactly.
That matched what my Dynon D10A and  steam altimeter showed.

I then spent several hours adjusting the  high and low pots on the alt 
encoder until the codes changed within 10  to 20 feet of the 50 foot 
points when applying vacuum to the static  system with a syringe. Can't 
get better that that, I  though.

Alas, after replacing the fuselage top and multitude of  screws, 
yesterday I hopped over to Cross City (CTY) a mere 15 miles  away.  I had 
to set the altimeter to 0.03 or 0.04 below what  their METAR reported in 
order to get altimeter to show their field  elevation -- 42 feet. 
Basically shows 30 to 50 feet too high altitude  if I set the Dynon to 
the reported pressure. All that work for  nothing!

Now I'm beginning to suspect that the pressures reported  by the METARs 
are not all that precise.
Checking METARS right now  at nearby airports, they range from 29.98 to 
30.02.

Any  suggestions on how to obtain an accurate air pressure  reference?

Finn


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<DIV>Ya,</DIV>
<DIV>&nbsp;</DIV>
<DIV>don't forget that the METAR suggested setting may be quite old and th=
e=20
reading not necessarily at your airport.</DIV>
<DIV>&nbsp;</DIV>
<DIV>The best way to set the Dynon, or any other altimeter is to use a=20
manometer. There are many tables that say what altitude is equivalent to=
 what=20
column of water (or mercury)..</DIV>
<DIV>&nbsp;</DIV>
<DIV>Easier to have a shop look at it and calibrate it.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Rich</DIV>
<DIV>&nbsp;</DIV>
<DIV>
<DIV>In a message dated 9/24/2015 11:42:18 A.M. Central Daylight Time,=20
flyrotary@lancaironline.net writes:</DIV>
<BLOCKQUOTE=20
style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"=
><FONT=20
  style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 face=3D=
Arial>
  <DIV class=3Dmoz-cite-prefix>On 9/24/2015 11:12 AM, ARGOLDMAN wrote:<BR>=
</DIV>
  <BLOCKQUOTE cite=3Dmid:list-8014916@logan.com type=3D"cite">
    <META name=3DGENERATOR content=3D"MSHTML 11.00.9600.18036"><FONT color=
=3D#000000=20
    size=3D2 face=3DArial>
    <DIV>Not sure that I understand completely, however the encoded altitu=
de has=20
    nothing to do with your local setting.</DIV></FONT></BLOCKQUOTE><FONT=
=20
  size=3D2><FONT face=3DArial>Yep. I set the Dynon to 29.92. Then the disp=
layed=20
  altitude should match what the encoder sends out.<BR><BR>Problem is how=
 to=20
  accurately (preferably to within 10 feet) calibrate the Dynon. Obviously=
 using=20
  nearby METAR reported pressures was not successful. And I'm beginning to=
 think=20
  that the instruments that reports pressure to METARs may not be all that=
=20
  accurate -- varies from airport to airport.<BR></FONT></FONT>
  <BLOCKQUOTE cite=3Dmid:list-8014916@logan.com type=3D"cite"><FONT color=
=3D#000000=20
    size=3D2 face=3DArial>
    <DIV>&nbsp;</DIV>
    <DIV>all encoders are calibrated to the same calibrations so that when=
 ATC=20
    or whoever reads the reply all of the aircraft that they are looking=
 at have=20
    the same altitude bias independent of errors in setting the kollsman=
 window=20
    in the various aircraft.</DIV>
    <DIV>&nbsp;</DIV>
    <DIV>Since you have gone into the encoder, there is a possibility that=
 the=20
    alterations that you have done may yield a constant error for ATC whic=
h is=20
    worse than not having an altitude report at all. You might want to hav=
e your=20
    encoder checked with proper instruments.</DIV>
    <DIV>&nbsp;</DIV>
    <DIV>Something that comes to mind is that since the encoder and the=20
    altimeter are both run from the static source, that there is a blockag=
e,=20
    kink, water etc that may be influencing the readings.</DIV>
    <DIV>&nbsp;</DIV>
    <DIV>Good luck in your quest for vertical reading stability</DIV>
    <DIV>&nbsp;</DIV>
    <DIV>Rich</DIV>
    <DIV>&nbsp;</DIV>
    <DIV>
    <DIV>In a message dated 9/24/2015 8:58:23 A.M. Central Daylight Time,=
 <A=20
    title=3Dmailto:flyrotary@lancaironline.net class=3Dmoz-txt-link-abbrev=
iated=20
    href=3D"mailto:flyrotary@lancaironline.net">flyrotary@lancaironline.ne=
t</A>=20
    writes:</DIV>
    <BLOCKQUOTE=20
    style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px so=
lid"><FONT=20
      style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 fac=
e=3DArial>Off=20
      topic, except it's in a 13B Van's RV-3 ;-)<BR><BR>Again, after flyin=
g home=20
      from Sun'n'Fun, ATC saw me several hundred feet <BR>below what I saw=
 on my=20
      altimeter.<BR><BR>Last week I finally got around to removing all the=
=20
      screws that holds the <BR>fuselage top over the instruments.<BR><BR>=
I=20
      hooked LEDs across the data lines that run from the altitude encoder=
=20
      <BR>to the transponder (gray code).<BR>(note that 1 is actually 0 vo=
lts --=20
      active low).<BR><BR>I checked METARs at nearby airports -- CTY, GNV.=
.. and=20
      I know my <BR>elevation exactly.<BR>That matched what my Dynon D10A=
 and=20
      steam altimeter showed.<BR><BR>I then spent several hours adjusting=
 the=20
      high and low pots on the alt <BR>encoder until the codes changed wit=
hin 10=20
      to 20 feet of the 50 foot <BR>points when applying vacuum to the sta=
tic=20
      system with a syringe. Can't <BR>get better that that, I=20
      though.<BR><BR>Alas, after replacing the fuselage top and multitude=
 of=20
      screws, <BR>yesterday I hopped over to Cross City (CTY) a mere 15 mi=
les=20
      away.&nbsp; I had <BR>to set the altimeter to 0.03 or 0.04 below wha=
t=20
      their METAR reported in <BR>order to get altimeter to show their fie=
ld=20
      elevation -- 42 feet. <BR>Basically shows 30 to 50 feet too high alt=
itude=20
      if I set the Dynon to <BR>the reported pressure. All that work for=
=20
      nothing!<BR><BR>Now I'm beginning to suspect that the pressures repo=
rted=20
      by the METARs <BR>are not all that precise.<BR>Checking METARS right=
 now=20
      at nearby airports, they range from 29.98 to <BR>30.02.<BR><BR>Any=
=20
      suggestions on how to obtain an accurate air pressure=20
      reference?<BR><BR>Finn<BR><BR><BR>--<BR>Homepage:&nbsp; <A=20
      title=3Dhttp://www.flyrotary.com/ class=3Dmoz-txt-link-freetext=20
      href=3D"http://www.flyrotary.com/">http://www.flyrotary.com/</A><BR>=
Archive=20
      and UnSub:&nbsp;&nbsp; <A=20
      title=3Dhttp://mail.lancaironline.net:81/lists/flyrotary/List.html=
=20
      class=3Dmoz-txt-link-freetext=20
      href=3D"http://mail.lancaironline.net:81/lists/flyrotary/List.html">=
http://mail.lancaironline.net:81/lists/flyrotary/List.html</A><BR></FONT><=
/BLOCKQUOTE></DIV></FONT></BLOCKQUOTE><BR></FONT></BLOCKQUOTE></DIV></FONT=
></BODY></HTML>
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