X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from rv-out-0910.google.com ([209.85.198.187] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2228217 for flyrotary@lancaironline.net; Thu, 02 Aug 2007 20:37:55 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.85.198.187; envelope-from=rwstracy@gmail.com Received: by rv-out-0910.google.com with SMTP id c27so478177rvf for ; Thu, 02 Aug 2007 17:37:17 -0700 (PDT) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:sender:to:subject:in-reply-to:mime-version:content-type:references:x-google-sender-auth; b=I34mtXT1ZbcrTHIEKcIqVfk8f3oqxVxjX7t2psdHWccDyAMKOlnNn8ugP1FqhrR+ppaPDhqr0eUqvIzuTtzVskMw/4IX1UEoDhIaVnBSwEZ0pCVhLYF03rcVQ/AYjCUKKXTd8HlyRmhZs+R5EjXnQIqXNL1nznNlmCidZrWJfWI= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:sender:to:subject:in-reply-to:mime-version:content-type:references:x-google-sender-auth; b=k0DL9XWR2VmNAPPtdvicsVpxtymCaqiIlxwwbiVVcpXFnNnqdaXXVJ3PfNGMfb5OVlYiCOFDW3sPsxNWNJeeqULsReyQWXhUr5VbYkzA6Xaf0Z4psF9+eLB/SVo1W6kkdrFBg8Cv4qhxgRQATKVZtqlNoh7g8iNOhak3uwoqIqg= Received: by 10.142.191.2 with SMTP id o2mr111537wff.1186101437828; Thu, 02 Aug 2007 17:37:17 -0700 (PDT) Received: by 10.142.115.16 with HTTP; Thu, 2 Aug 2007 17:37:17 -0700 (PDT) Message-ID: <1b4b137c0708021737r696244caw846e7b8080575217@mail.gmail.com> Date: Thu, 2 Aug 2007 20:37:17 -0400 From: "Tracy Crook" Sender: rwstracy@gmail.com To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] Re: EM2 & builder issues In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_85487_6791334.1186101437785" References: X-Google-Sender-Auth: d31dec9651da0fd7 ------=_Part_85487_6791334.1186101437785 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Wendell, Yep, in fact the OAT and the 2 aux air temp channels use the LM34 part and your suggestion on making them work for liquid temp use works fine. I'm not sure what the average builder would think about having to do this though. The liquid temp channels (coolant, oil & 2 aux liquid temp channels) on the EM2 are set up for resistive type sensors (rather than voltage) so the LM34s won't work on them. I could have made all the channels user programmable for sensor type but even I thought that would be going a bit too far. Tracy On 8/2/07, Wendell Voto wrote: > > Tracy, > Maybe you shouldn't had said 50th but we won't tell. > Could the EM2 use LM34 temp sensors? They give 10mv/deg. F and have very > good accuracy (spec is 1 degree but I get less than .1 degree repeatability > one sensor to another)and track well, very linear. They are what I am > using, just JB welded into a hollowed out old sensor and plan on using for > oil and water temps. > Wendell > > *Fine points on the EM2:* > > > > The default sensors on the EM2 are very low cost automotive types but they > are not inherently super accurate. Usually there in no big down-side for > the water or oil temp to be off a few degrees so most builders need not go > any further. If the water temp turns out to be actually 178 instead of > 180, no big deal. Super accuracy can be had with these sensors if you go to > the trouble of calibrating the instrument but then you must get into the > nitty gritty of the calibration procedures and the troubles can begin. > > But here is where it does matter. If you are calculating thermal loads > and heat dissipation based on differential temps (let's say water temps in > and out of the radiator for instance) a few degrees of error can make your > results meaningless. In this example, it is not uncommon for the Delta T to > be in the range of 10 degrees at some power settings. If the error in > temperature is a couple of degrees, the error is huge, especially if the > errors are in opposite directions. > > Bottom line is, if you need very accurate readings, learn to calibrate the > EM2 if that is what you are using. To do this, you need a good reference. > The easiest way is to use a non-contact (infra-red) thermometer. Harbor > Freight and others are now selling inexpensive ones for about $10.00. No > reason for any airplane builder not to have one. Be sure to paint the test > points on the part to be measured with a spot of flat black paint to > eliminate emissivity errors. > > Tracy (should I have said 50th? ) > > > > > > > ------=_Part_85487_6791334.1186101437785 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline
Wendell,
Yep, in fact the OAT and the 2 aux air temp channels use the LM34 part and your suggestion on making them work for liquid temp use works fine.  I'm not sure what the average builder would think about having to do this though.
 
The liquid temp channels (coolant, oil & 2 aux liquid temp channels) on the EM2 are set up for resistive type sensors (rather than voltage) so the LM34s won't work on them.  I could have made all the channels user programmable for sensor type but even I thought that would be going a bit too far. 
 
Tracy

 
On 8/2/07, Wendell Voto <jwvoto@itlnet.net> wrote:
Tracy,
Maybe you shouldn't had said 50th but we won't tell.
Could the EM2 use LM34 temp sensors?  They give 10mv/deg. F and have very good accuracy (spec is 1 degree but I get less than .1 degree repeatability one sensor to another)and track well, very linear.  They are what I am using, just JB welded into a hollowed out old sensor and plan on using for oil and water temps.
Wendell
Fine points on the EM2:
 
 
 
The default sensors on the EM2 are very low cost automotive types but they are not inherently super accurate.  Usually there in no big down-side for the water or oil temp to be off a few degrees so most builders need not go any further.  If the water temp turns out to be actually 178 instead of  180, no big deal.  Super accuracy can be had with these sensors if you go to the trouble of calibrating the instrument but then you must get into the nitty gritty of the calibration procedures and the troubles can begin.
 
But here is where it does matter.  If you are calculating thermal loads and heat dissipation based on differential temps (let's say water temps in and out of the radiator for instance)  a few degrees of error can make your results meaningless.  In this example, it is not uncommon for the Delta T to be in the range of 10 degrees at some power settings.  If the error in temperature is a couple of degrees, the error is huge, especially if the errors are in opposite directions.
 
Bottom line is, if you need very accurate readings, learn to calibrate the EM2 if that is what you are using.  To do this, you need a good reference.  The easiest way is to use a non-contact (infra-red) thermometer.  Harbor Freight and others are now selling inexpensive ones for about $10.00.  No reason for any airplane builder not to have one.   Be sure to paint the test points on the part to be measured with a spot of flat black paint to eliminate emissivity errors. 
 
Tracy  (should I have said 50th?  )
 
 

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