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	Subject - Type K Thermocouple JimmyDee A question came up on another forum about the thermocouple used for an engine, exhaust pyrometer. Typically a type k thermocouple is used and some of the meters are fed directly and others go through an amplifier. My question is, are a type k thermocouples fairly much the same or do they vary considerably? I do realize some react in different time frames and they may vary in size, but do they give the same voltage reference for a given temperature? Jim Scott Vickrey Jimmy I have a reference sheet for this at home. I'm in Dallas now, but when I get home I'll look for it. JimmyDee Thanks. I was of the understanding that the voltage was fairly consistant for a given temperature with the type K. Jim Scott Vickrey I can't find the chart I told you about. It might be in storage. K thermocouples are the most common type. They have a wide range and are good in an oxidizing environment. They have two grades Class 1 and 2, Class 1 are the more accurate of the two. The higher the temperature the more accurate they are. The voltage characteristics should remain fairly constant as long as the alloys are constant. If the thermocouples are purchased from the same manufacturer then recalibration may not be necessary as they should have similar characteristics. RTDs are better for lower temperatures(<300C). Chris Clement RTD's are a better way to go. We used them up to 1000 deg F in the power plants. JimmyDee Chris, the thermocouple I'm referring to is directly in the flame of the exhaust on a diesel engine. + or - 25 degrees would not be a big deal. Temps can reach as high as 1600 F for short periods of time. (Longer at that temp, the pistons melt)Most if not all engine manufactures and gauge manufactures use thermocouples for this application. It is important on these engines to keep the exhaust temps below 1300 degrees to prevent damage to the engine. Running the engine stock, they are adjusted so the livability of reaching 1300 is improbable. However with a chip enhancement, 1500 is an easy target. Brad Selmon I sell and service Chart recorders and the millivolt curves for thermocouples and RTDs are universal. You can any wire from any vendor and put into another vendors instrument. All you have to do is know your type (i.e. type K). The accuracy on a T/C is 2% the accuracy on a 3 wire RTD is 0.1%. There is an obvious cost difference. You can make a working thermcouple yourself ,by buying some extension wire and twisting One end (the sensing side, Hot Junction). The different thermocouple types are determined by the different material combinations. Some are for higher temps. The LL Bean of Industrial Thermcouple is Omega. They have more info on their site. http://www.omega.com/prodinfo/thermocouple.html JimmyDee Thanks for that answer. I was told in no uncertain terms that you had to stay with the thermocouple that the gauge manufacturer used for their particular gauge and it didn't sound right to me. Type K is type K right. So that would mean that anyones type K thermocouple would work with anyone else's gauge if that is correct. Jim Brad Selmon Jim, You are right for thermocouples. For RTDs (resistance temperature devices) you have to keep the same gauge wire or correct the change in resistance and impedence of the new/ different extension wire at the electronics. I logged onto this site to learn about 3 phase electrical installations for things like motors and vfds. Have there been any posts for that? JimmyDee There have been a few. If you have questions, go ahead and ask them. I've worked with both and so have others on here. Get it started by asking a few questions and lets see where it will go. Jim