error in Volt to Temp conversion Type E

[nitad54448]

Hi

I think that there is an error in the Volts to Temperature vi in Labview, for type E thermocouple,.... at low temperature.

According to the tables the voltage for a E type thermocouple at 13K should be -0.009797.

the Temperature to Volts.vi in labview gives the correct values.

Now putting -0.009797 V in the Volts to Temperature vi will give 25.8 K

Can anyone confirm this error ?

thanks

N

Edit note : I see in the vi that the conversion V to T is valid for T>70 K (albeit T to V is valid from 4K... as it is the type E thermocouple !)

[GerdW]

Hi N,

why don't you read the comments on the blockdiagram inside this VI?

For TC type E it clearly states:

temperature range: -200 C to 0 C: error range:  0.03 C to -0.01 C

So why do you expect correct values at 13K when the formula used is only valid starting from >73K?

Btw. type E thermocouples are recommended to be used at ranges from -200 to +900°C, other sources mention -50 to +740°C! Do you really want to use type E at 13K?

[nitad54448]

Hi

I read the comments (too late), see my PS note.

For type E thermocouples other sources mention 4K to 400 K, it is actually commonly used in cryogenics at 4K.

N

[johnsold]

The Temperature to Volts and Volts to Temperature VIs must be used with a good deal of caution. The temperature and voltage ranges are not the same in both directions for some types of thermocouples.  This is not a problem with the NI implementation but a limitation of the NIST documents from which the VIs were derived.  Read the help files carefully.  Outside the specified ranges the errors can get very large, very quickly.

Lynn

[nitad54448]

Hi

Yes, you are right. There is no problem with the vi (I just read the "small print" after posting) but the ITS90 polyomials which do not cover temperature below -200 °Cin Volt to Temperarure.vi

I should change the title of this post.

Anyway, I took the data and fitted two more regions and added to my vi.

thanks for ehlp

regards

N