![]() ![]() Otherwise you are just producing a meaningless voltage reading. Remember that a thermocouple produces a voltage because of a difference in temperature, and so because we are looking for a difference, we must have something to reference against. The confusion is coming from the fact that you cannot get the information you want with the information you are using. However at the bare minimum to clear things up you must know that thermocouples operate on the seebek effect, and essentially produces a voltage based on a difference in temperature between 2 different metals. I won't go into a lot of depth about how thermocouples work because it involves quantum mechanics and would sort of stray from the original point of the question. I realise this thread is kinda old but in case anyone else in the future is curious I will explain why there is confusion and how these charts work. The reference book I have available to me was in Fahrenheit, but 68F -> 1.306mV:Īll of the values seem to differ by 10C (1.019 mV vs 1.537 mV), except the Fahrenheit value seems to be about halfway, so I'm sure it's no coincidence that my interpretations of the charts are wrong, but using the calculators I just punched it in. ![]() Is looking up a cold junction offset value in any way different than looking up a regular value? In my example problem, I went to my chart to find the mV for 20C, should I be looking at a different chart for cold junctions?įrom my sample problem textbook, they found 20C -> 1.537 mV:įrom an online chart, I also found 20C -> 1.537 mV:įrom another chart online, I found 20C -> 1.019 mV:Īn online calculator I found says 20C -> 1.019 mV:įluke's online calculator agrees 20C -> 1.019mV: Related to #1, is there a case to use one or the other above? These appear the same, but the value that I add to or subtract from is always a mystery, specifically because all charts seem to have a far left value and far right value that are the same, and for me it would be intuitive if the right value was always +10. Some charts number from -10 to 0 in columns, others number from 0 to +10 in columns. I seem to also have found multiple charts and online calculators that contradict eachother, so if somebody could please help me work this out it would be greatly appreciated.Īs far as I can tell, my sources of confusion come from these questions: I know I have to account for the junction temperature by adding the voltage at 20C to my measured voltage, then looking up the result in the chart. How to solve the problem is straight forward. Specifically, I have a sample problem in a study guide where the measured voltage is 21.57 mV with a 20C junction and a Type J thermocouple. It's accuracy is guaranteed over a limited temperature range.Studying for the PE exam, everything seems to be a breeze, but I cannot for the life of me read a TC chart. Thermocouple EXTENSION Wire is used to connect Thermocouples to Instrumentation. Please contact a Thermal Advisor to request Special Limits This wire is available in standard limits ☒☌ or Special Limits ☑☌. J Thermocouple Grade wire always has a BROWN jacket ( Teflon or Fiberglass ) with White and Red conductors. Thermocouple GRADE Wire is recommended for measuring process temperature. Note: RED is always Negative "–" in the thermocouple world! Maximum continuous temperature is around 750☌ / 1,400☏ depending on wire gauge size. Some of our clients use gold plated thermocouple connectors if "J" wire is used outdoors. Be careful of the IRON leg because its alloy will rust if exposed to moisture. Type J wire is commonly found in Industrial applications. ![]() It's accuracy is comparable to type "K", and has a wide temperature range. It’s remains popular with installations that already have existing "J" thermocouples installed. Type J Thermocouple(Iron+ / Constantan –) J was a commonly used thermocouple wire. ![]()
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