James26
Posts: 22
Joined: Mon Jul 22, 2013 12:14 pm

Thermocouple data logger

Tue Aug 27, 2013 7:36 am

Hi there,

I have been working on a project to read temperature from a thermocouple using a Gertboard/Rpi.

I have a code written in C which I have tested using function generator to ensure its operation and it does work as I expect.

I have been using LTK001 which is a cold junction compensator and matched amplifier in order to have values my ADC is able to read...
Now, the thing I am confused about at the moment is how I manage to match the outputs from amplifier/compensator to the needs of gertboard

I have an equation in my code that makes my limits operate between 0v and 3.3v. my limits are -65 --> +130. So 0v = -65 and 3.3v = +130.

What I am confused about is how to I work out what mv/degree c I need to produce from my amplifier/compensator circuit for it to match with my gertboard. If that makes sense ?

Thanks, James.

LesTroyer
Posts: 14
Joined: Wed Aug 29, 2012 2:38 pm

Re: Thermocouple data logger

Tue Aug 27, 2013 2:07 pm

you might try something like a MAX6675 you read the TC directly in deg C. it interfaces with SPI so easy to hook up. I think there is an I2C version as well if that is more to your liking.

python libs arlready exist to read the chip.

James26
Posts: 22
Joined: Mon Jul 22, 2013 12:14 pm

Re: Thermocouple data logger

Wed Aug 28, 2013 7:42 am

Sorry dont think I explained very well,

This is a project I have been given and due to certain requirements for it I am only allowed to use a type T thermocouple therefore I can't use the MAX amplifiers.

I have my circuit wired up http://www.google.co.uk/imgres?q=ltk001 ... x=80&ty=31 similair to this but replacing the 255k with a 1.56M to give my required gain.

Now my problem isnt noticed at first as when i heat up the thermocouple it shows on the computer the corresponding bits/voltage/temperature and appears to work.
Although, when I put a handheld thermometer next to the thermocouple it tells me for example that I am at 50 degrees c, when the computer believes we are at a maximum of 130 degrees c.
I adjusted the gain of the amplifier with respect to the voltage/temperature i should get at room temp and these are fine but everything else seems to be skewed.

Any ideas?

User avatar
robin48gx
Posts: 17
Joined: Mon Jul 16, 2012 11:20 am
Location: Brighton

Re: Thermocouple data logger

Mon Nov 19, 2018 9:21 am

You could use a TH7. Thats a board I made with my son (now at uni) last summer.
Its at version 4 and detects loss of thermocouple and applies compensation
in s/w.
It does the cold Jucntion compensation in s/w. So Type T is a matter of finding the right
polynomials. Currently we only implemented `k' because they were easier to find/buy.

Look at the git s/w here and https://www.omega.com/techref/pdf/z198-201.pdf.

If you want to put T type polynomials into the python code feel free to branch off
the git repo https://github.com/robin48gx/TH7

Mikhan
Posts: 1
Joined: Wed Nov 13, 2019 10:33 pm

Re: Thermocouple data logger

Wed Nov 13, 2019 10:38 pm

To robin48gx
Could you please let me know where I can purchase TH7 boards? Thanks
robin48gx wrote: You could use a TH7. Thats a board I made with my son (now at uni) last summer.
Its at version 4 and detects loss of thermocouple and applies compensation
in s/w.
It does the cold Jucntion compensation in s/w. So Type T is a matter of finding the right
polynomials. Currently we only implemented `k' because they were easier to find/buy.

Look at the git s/w here and https://www.omega.com/techref/pdf/z198-201.pdf.

If you want to put T type polynomials into the python code feel free to branch off
the git repo https://github.com/robin48gx/TH7

User avatar
robin48gx
Posts: 17
Joined: Mon Jul 16, 2012 11:20 am
Location: Brighton

Re: Thermocouple data logger

Fri Feb 21, 2020 2:32 pm


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