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.
Re: Thermocouple data logger
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.
python libs arlready exist to read the chip.
Re: Thermocouple data logger
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?
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?
Re: Thermocouple data logger
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
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
Re: Thermocouple data logger
To robin48gx
Could you please let me know where I can purchase TH7 boards? Thanks
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