Return-Path: Received: from tomcat.al.noaa.gov ([140.172.240.2] verified) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 526322 for flyrotary@lancaironline.net; Wed, 10 Nov 2004 12:21:58 -0500 Received-SPF: none receiver=logan.com; client-ip=140.172.240.2; envelope-from=bdube@al.noaa.gov Received: from PILEUS.al.noaa.gov (pileus.al.noaa.gov [140.172.241.195]) by tomcat.al.noaa.gov (8.12.0/8.12.0) with ESMTP id iAAHLRbe023117 for ; Wed, 10 Nov 2004 10:21:27 -0700 (MST) Message-Id: <5.2.1.1.0.20041110085020.088cab50@mailsrvr.al.noaa.gov> X-Sender: bdube@mailsrvr.al.noaa.gov X-Mailer: QUALCOMM Windows Eudora Version 5.2.1 Date: Wed, 10 Nov 2004 10:21:36 -0700 To: "Rotary motors in aircraft" From: Bill Dube Subject: Thermocouples (was: EGT sensors) In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed At 10:36 AM 11/10/2004 -0500, you wrote: >Al Gietzen wrote: > >>Subject: [FlyRotary] EGT sensors >> >> >>Time to change the EWP subject:) >>At the rotary roundup Tracy mentioned that if you have two EGT sensors, you >>can tune each rotor separately. Does anybody have two EGT sensors, how they >>are mounted and where do you get them? >>Bulent >>----- >>I have three (20B) inconel clad K-type, clamp-in. One in each header a >>couple inches from the port. Got mine from Grand Rapids Technologies, but >>you may alos be able to get them from Omega. They are built into a hose >>clamp so you drill the hole, tighten the clamp, seal up tight. >> >>Al >Don't you mean J-type? I believe K is lower temperature. The opposite is true. The ASTM recommends that type J be used continuously only to 760 C (1400 F). Type K are rate for continuous use up to 1260 C (2300 F). With modern metering, type K thermocouples are superior to type J. The copper lead in type J is a high thermal conductor that transports heat to (or away) from the tip, resulting in increased error in the measurement. The copper also oxidizes easily. Copper oxide has an enormous Seebeck coefficient, so the calibration goes out the window if the wire or the connections corrode. The main reason that type J was popular was that it has a very flat Seebeck coefficient (as a function of temperature.) This makes the temperature (roughly) proportional to the voltage over a pretty good range. The Seebeck coefficient for type K varies quite a bit with temperature. This makes it hard to build a simple analog readout, but is not a problem for a modern electronic readout.