X-Virus-Scanned: clean according to Sophos on Logan.com From: Received: from omr-m008e.mx.aol.com ([204.29.186.7] verified) by logan.com (CommuniGate Pro SMTP 6.1.5) with ESMTPS id 8015150 for flyrotary@lancaironline.net; Thu, 24 Sep 2015 13:36:39 -0400 Received-SPF: pass receiver=logan.com; client-ip=204.29.186.7; envelope-from=ARGOLDMAN@aol.com Received: from mtaomg-mbd02.mx.aol.com (mtaomg-mbd02.mx.aol.com [172.26.252.16]) by omr-m008e.mx.aol.com (Outbound Mail Relay) with ESMTP id 1FBC53800109 for ; Thu, 24 Sep 2015 13:36:04 -0400 (EDT) Received: from core-mxb004c.mail.aol.com (core-mxb004.mail.aol.com [172.29.192.141]) by mtaomg-mbd02.mx.aol.com (OMAG/Core Interface) with ESMTP id 7162E38000082 for ; Thu, 24 Sep 2015 13:36:02 -0400 (EDT) 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 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_19d3c6.5d7fe5.43358e82_boundary" X-Mailer: Unknown sub 13 X-Originating-IP: [50.151.84.32] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1443116164; bh=RjYr7Mf4grSI0naGqB6YqzcMMbAH7X+5mWe4QBYUkQU=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=sXxUXkvBaOUeaRcccmRQ2O8QYHTTCrE899nDU0ciYSf7yWNxzDPqB7jCrul5Iy5EN r5khPxqaZSqieb2gDGmmO1QsicuAuDFn0ogaAD8rA0CJr0vQylhe1D7QqvQIsUExJj z2sgDzWfV8qovVP/op0CvM+ILh6ZerjuRGGhq2IY= x-aol-sid: 3039ac1afc10560434825ae7 --part1_19d3c6.5d7fe5.43358e82_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit 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 -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html --part1_19d3c6.5d7fe5.43358e82_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Ya,
 
don't forget that the METAR suggested setting may be quite old and th= e=20 reading not necessarily at your airport.
 
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)..
 
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,=20 flyrotary@lancaironline.net writes:
On 9/24/2015 11:12 AM, ARGOLDMAN wrote:
=
Not sure that I understand completely, however the encoded altitu= de has=20 nothing to do with your local setting.
Yep. I set the Dynon to 29.92. Then the disp= layed=20 altitude should match what the encoder sends out.

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.
 
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.
 
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.
 
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.
 
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.ne= t=20 writes:
Off=20 topic, except it's in a 13B Van's RV-3 ;-)

Again, after flyin= g home=20 from Sun'n'Fun, ATC saw me several hundred feet
below what I saw= on my=20 altimeter.

Last week I finally got around to removing all the= =20 screws that holds the
fuselage top over the instruments.

= I=20 hooked LEDs across the data lines that run from the altitude encoder= =20
to the transponder (gray code).
(note that 1 is actually 0 vo= lts --=20 active low).

I checked METARs at nearby airports -- CTY, GNV.= .. and=20 I know my
elevation exactly.
That matched what my Dynon D10A= and=20 steam altimeter showed.

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

Alas, after replacing the fuselage top and multitude= of=20 screws,
yesterday I hopped over to Cross City (CTY) a mere 15 mi= les=20 away.  I had
to set the altimeter to 0.03 or 0.04 below wha= t=20 their METAR reported in
order to get altimeter to show their fie= ld=20 elevation -- 42 feet.
Basically shows 30 to 50 feet too high alt= itude=20 if I set the Dynon to
the reported pressure. All that work for= =20 nothing!

Now I'm beginning to suspect that the pressures repo= rted=20 by the METARs
are not all that precise.
Checking METARS right= now=20 at nearby airports, they range from 29.98 to
30.02.

Any= =20 suggestions on how to obtain an accurate air pressure=20 reference?

Finn


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