Library for Thermocouple based on NIST ITS-90 Database

The National Institute of Standards and Technology (NIST) has published the data of several thermocouples as NIST ITS-90 Thermocouple Database.

The data consists of three parts for each thermocouple:

1. table of the thermoelectromotive forces with respect to 0 degree Celsius for each 1 degree Celsius of temperature difference

2. (coefficients for) approximate formula for conversion from temperature to thermoelectromotive force

3. (coefficients for) approximate formula for conversion from thermoelectromotive force to temperature

This library provides functions based on 2. and 3. above. This allows mutual conversion between the emf (electromotive force) of the thermocouple and temperature with respect to $0\,\degree\mathrm{C}$.

The following functions are provided in this library. Replace X in the function name with the thermocouple types (B, E, …).

FLOAT temp2emf_X(FLOAT temperature)

Calculates the emf from the given temperature. It returns NAN (not a number) if the specified temperature is out of range,

FLOAT emf2temp_X(FLOAT emf)

Calculates the temperature from the given emf (with respect to $0\,\degree\mathrm{C}$). It returns NAN (not a number) if emf is out of range,

First, retrieve the files from the repository.

git clone https://github.com/TPKato/nist-its90

The minimum file requirements are as follows:

• nist-its90.c

• nist-its90-X.c (X should be replaced by the thermocouple type (B, E, …))

• nist-its90.h

• nist-its90-config.h

If you use this library with your C source code(s):

1. Edit nist-its90-config.h as necessary.

2. Add following lines in your code:

   #include <math.h>	/* Only for type K (which requires exp()) */
   #include "nist-its90.h"

3. The compilation procedure is as follows:

   gcc -c nist-its90.c
   gcc -c nist-its90-K.c
   gcc -o [execfile] [your source].c nist-its90.o nist-its90-K.o -lm

For Arduino, the procedure is almost the same.

1. Copy the necessary files to the project directory.

2. Edit nist-its90-config.h if necessary.

3. Add the following line to the .ino file.

   #include "nist-its90.h"

t = emf2temp_K(emf + temp2emf_K(t_amb));

This library consists of the following files.

Makefile

This file is used to generate nist-its90-*.c and nist-its90.h from the NIST database.

nistcoeff.pl

A Script to generate nist-its90-*.c and nist-its90.h from the NIST database

nist-test.pl

Test of generated programs

nist-its90.c

Compute polynomials (using the Horner method)

The following are the files generated by nistcoeff.pl. These files can be generated using the above files, but you usually do not need to generate them by yourself, since they are included in the repository.

• nist-its90-B.c

• nist-its90-E.c

• nist-its90-J.c

• nist-its90-K.c

• nist-its90-N.c

• nist-its90-R.c

• nist-its90-S.c

• nist-its90-T.c

• nist-its90.h

make
make test

See Correcting Temperature Data of MAX31855 for information on how to use this library with MAX31855 (Cold-Junction Compensated Thermocouple-to-Digital Converter by Maxim Integrated).

• https://github.com/TPKato/nist-its90

• MIT License