k type thermocouple (chromel/alumel) range and accuracy

[engr_joni_ee]

Hi,

I am wondering about the range and accuracy of the k type (chromel/alumel) thermocouples. In some reference it -270 C to 1372 C.

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But I guess it the range and accuracy is also limited by the device/reader electronics. Is it also limited by the type of wire used ? I have found some thermocouple with plug that can be connected to the device/reader and they come with different range which I don't understand but I get an impression that in addition to the limitation put by the device/reader electronics, the limitation also come with the type and maybe length of the wire. Am I understanding it correct ?

 

[KlausST]

Hi,

As with every measurement device:
* There is a theoretical optimum
* and there are errors

Then length of a wire - per se - is not the problem. But introduced noise, impedance, material, leakage current ...

And amplifiers also introduce errors (offset, gain, linearity..), and the cold junction compensation, the software, the linearisation....

Nothing special to thermocouple.

If you want high accuracy, the effort becomes huge.

***
All the physics and math is known. But some designers simply don´t care that much about it.
Some killers for thermocouple performance:
* wrong cable (they need to have the same two materials as the thermocouple itself)
* noise, and/or missing filters
* (offset) drift of OPAMP
* wrong software/linearisation.

Klaus

 

[engr_joni_ee]

Apart from the limitations but by the electronics of the device/reader, how the thermocouple probe itself put the limit on temperature range ?

 

[KlausST]

Hi,

I can only guess: the isolation material.
***
So if you want a sensor for higher temperature, then byu the correct one.
***
Since this is very specific to the one sensor you use: Read the datasheet and if this gives no satisfying result: Contact the manufacturer.

We don´t even know which manufacturer and type you are talking about.

Klaus

 

[engr_joni_ee]

I am looking for the k-type thermocouple that I can connect to Extech EA15 to cover the range between -180 C to + 180 C. Any suggestion ?

 

[Easy peasy]

With careful connections you can get 0.1 deg C accuracy ...