X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 26 Mar 2014 12:04:22 -0400 Message-ID: X-Original-Return-Path: Received: from mail-pb0-f51.google.com ([209.85.160.51] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6800646 for lml@lancaironline.net; Wed, 26 Mar 2014 09:01:43 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.85.160.51; envelope-from=frederickemoreno@gmail.com Received: by mail-pb0-f51.google.com with SMTP id uo5so1895704pbc.24 for ; Wed, 26 Mar 2014 06:01:08 -0700 (PDT) X-Received: by 10.66.233.99 with SMTP id tv3mr4445912pac.97.1395838867984; Wed, 26 Mar 2014 06:01:07 -0700 (PDT) X-Original-Return-Path: Received: from User-PC (CPE-124-178-172-69.lns3.wel.bigpond.net.au. [124.178.172.69]) by mx.google.com with ESMTPSA id pr4sm58032529pbb.53.2014.03.26.06.01.05 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 26 Mar 2014 06:01:06 -0700 (PDT) MIME-Version: 1.0 X-Original-Message-Id: <5332CF89.000146.07432@USER-PC> X-Original-Date: Wed, 26 Mar 2014 21:00:57 +0800 Content-Type: Multipart/Alternative; charset="iso-8859-1"; boundary="------------Boundary-00=_L5O1LD9K8WA1VA400000" X-Mailer: IncrediMail (6605288) From: "frederickemoreno@gmail.com" X-FID: FLAVOR00-NONE-0000-0000-000000000000 X-Priority: 3 X-Original-To: "Lancair Mail (lml@lancaironline.net)" Subject: TSIO 550 temp sensors --------------Boundary-00=_L5O1LD9K8WA1VA400000 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Temperature sensors are by far the least reliable sensors on the engine, = and the TIT/EGT are the least reliable of temperature sensors due to the high temperatures and vibration they must endure. =0D =0D This is dredging back many years, but I'll give the old memory neurons a = try =0D =0D Modern instruments seem to use K type (chromel/alumel) thermocouples everywhere when in years past they were only used for high temperatures.=20 They have poor output signals at lower temperatures (as with CHTs and Oil temp). Oil temperature used to be measured with Copper-Constantan thermocouples because of better output characteristics at lower temperatu= res =0D =0D Now with sensitive digital electronics capable of handling non linear calibration curves and tiny input voltages, even these little little sign= als are enough to be detected, corrected for non-linearities, and then used f= or sufficiently accurate displays in our planes. So type K is being used mo= re and more.=0D =0D However......=0D =0D Measuring comparatively low temperatures (compared to EGT/TIT), these tin= y signals can be easily fouled up by dirty connectors, intermittent connections caused by the small but stiff thermocouple wire wiggling and breaking, and other mechanical and electrical resistance faults. It is j= ust the nature of the beast. =0D =0D My MVP 50 engine monitor reads OAT from a thermocouple in my cabin vent NACA duct, and last flight decided to start indicating numbers way above = and below the real OAT. Looks like a classic intermittent connection problem= =2E I checked the probe wires today (easy to get to) and wiggled the connector = on the data box (hard to get to) while a friend watched the readout, but we could not induce an error. Also classic intermittent behavior. My bet: = it will show up next flight, or the flight after that, after a bit of vibrat= ion exposure. Or it could be a short in the thermocouple wiring somewhere whi= ch creates a secondary thermocouple at the short (different location and temperature) that fouls the output of the primary thermocouple. As noted thermocouple wire is stiff and difficult material, not forgiving like multi-strand copper. =0D =0D Bottom line: suspect connections and wiring as much as the thermocouple junction inside the sheath or fitting. Check for large enough service loops to absorb vibration, but not so long as to allow the wire to flex between tie downs. =0D =0D Fred Moreno --------------Boundary-00=_L5O1LD9K8WA1VA400000 Content-Type: Text/HTML; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Temperature sensors are by far the least reliable sensors on the eng= ine, and the TIT/EGT are the least reliable of temperature sensors due to= the high temperatures and vibration they must endure. 
 
This is dredging back many years, but I'll give the old memory neuro= ns a try.
 
Modern instruments seem to use K type (chromel/alumel) thermocouples= everywhere when in years past they were only used for high temperatures.=   They have poor output signals at lower temperatures (as with CHTs = and Oil temp).  Oil temperature used to be measured with Copper-Cons= tantan thermocouples because of better output characteristics at lower te= mperatures. 
 
Now with sensitive digital electronics capable of handling non linea= r calibration curves and tiny input voltages, even these little litt= le signals are enough to be detected, corrected for non-linearities, and = then used for sufficiently accurate displays in our planes.  So type= K is being used more and more.
 
However......
 
Measuring comparatively low temperatures (compared to EGT/TIT), thes= e tiny signals can be easily fouled up by dirty connectors, intermittent = connections caused by the small but stiff thermocouple wire wiggling and = breaking, and other mechanical and electrical resistance faults.  It= is just the nature of the beast. 
 
 My MVP 50 engine monitor reads OAT from a thermocouple in my c= abin vent NACA duct, and last flight decided to start indicating numbers = way above and below the real OAT.  Looks like a classic intermittent= connection problem. I checked the probe wires today (easy to get to) and= wiggled the connector on the data box (hard to get to) while a friend wa= tched the readout, but we could not induce an error.  Also classic i= ntermittent behavior.  My bet: it will show up next flight, or the f= light after that, after a bit of vibration exposure. Or it could be a sho= rt in the thermocouple wiring somewhere which creates a secondary thermoc= ouple at the short (different location and temperature) that fouls t= he output of the primary thermocouple.  As noted thermocouple wire i= s stiff and difficult material, not forgiving like multi-strand copper. <= /DIV>
 
Bottom line: suspect connections and wiring as much as the thermocou= ple junction inside the sheath or fitting.    Check for la= rge enough service loops to absorb vibration, but not so long as to allow= the wire to flex between tie downs.
 
Fred Moreno
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