What is a Thermocouples true range.

randy741985

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Oct 2006
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Looking at thermocouple ranges on the internet, they very mixed.
you will find type J measures up to 2000F other say 1500F, 1400F.

Type K 2200F to 2500F.

using Omega site it list Type J scale to 32F to 1382F
type K -328 to 2282F.

Just thought this was interesting.

thnaks for any input.
 
I worked at a firm that built wood fired burners. At the throat of the furnace, we measured the output, typically at up to 2200F. However, those TC's were encased in a 3/4" diameter Ceramic tube and the TC wire itself consisted of #8AWG TC wire. Very heavy to withstand the heat. Smaller sizes don't last very long at those temperatures. Smaller responds to temperature changes faster, but aren't as robust. They were type K and were wired to 4/20maDC converter modules. They were about 3' long to get the "head" end well outside the heating zone. We went by the Omega listings and most of the TC's were from Omega. Just FYI..
 
I would trust the Omega site. They are a big name with good data. All my thermocouple Temp vs. Voltage charts come from Omega as well.
 
Maybe a little over simplistic but my thought is that from a control standpoint it doesn't matter. What matters is the signal conditioner or input card you put the T/C into. This is the range usable by yourcontrol process.

Now I have never worked near the end of a range of a T/C or On a bight heat load system so there are definately other considerations and indeed the materials and type of construction could be very different even for the same letter designation and limit it more than the simple physics of the metal joint. So I guess they all could be right for their particular design.
 
The temperature rating accounts for the sheath material as well. For example a Type K T/C in a stainless steel sheath is rated to 900C, but the same T/C in an inconel sheath can be rated to 1200C, while the Type K T/C range covers up to 1370C. Atmospheric conditions should be considered as well. A type K TC can be used at higher temperatures in a vacuum or a reducing atmosphere, but should be derated when used in an oxidizing atmosphere.
 
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The max temp is the temp nothing will happen with the sensor, like oxidation, melting etc. or the insulation will melt are become glass or something other.
it is absolute temp not the difference between the sensor and the CJ.
 
It is my opinion that, as Shooter implied, the limitation on the T/C are physical destruction and not output. A T/C creates a voltage as a function of its temperature. This is non-linear, and the voltage temperature relationship varies dpending on the two metals at the hot juncion. I think that the useable range is more a function of the degree of non-linearity at various temperatures, and depending on the supplier (and the transmitter if used) the defined range will vary.
 
Thanks For the Input,

I asked because if I were scaling this in a PID what should be my max scale.

Other words if brought a T/C in as scaled for pid 0-16383 what would be
MIN. and MAX.?


Thanks In advance.
 
It would be whatever value 16383 represents in your hardware, not the value from your sensor. Eg, if your PLC TC input card specified that 16383 was 1370C then that is what you would use.

Be careful and check your specs, most T/C cards perform the linearization for you and return a value in engineering units.
 
It would be whatever value 16383 represents in your hardware, not the value from your sensor. Eg, if your PLC TC input card specified that 16383 was 1370C then that is what you would use.

Be careful and check your specs, most T/C cards perform the linearization for you and return a value in engineering units.


Thanks
 

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