Hello,
for my project I use a Adafruit Universal Thermocouple Amplifier MAX31856 (Breakout) with a Type T cable to measure temperatures in the area of liquid Nitrogen (-196 °C). The room temperature is shown correct (23 °C), but if I try to measure the temperature on a metal plate on the surface of the liquid Nitrogen I got a temperature round about -240 °C. This is not possible, because the normal temperature measure devise (which I used to compare the temperatures) shows -190 °C and the highest possible temperature could be not lower then -196°C (cause of the liquid Nitrogen). Also the description of this thermocouple says (on the Adafruit website) that this one has a measure area from "-210°C to +1800°C" with a precision of "output in 0.0078125° resolution". So what can I do?
Thank you in advance and best regards
Erik
Adafruit Universal Thermocouple Amplifier MAX31856
Moderators: adafruit_support_bill, adafruit
Please be positive and constructive with your questions and comments.
- ericson95
- Posts: 12
- Joined: Tue Jun 01, 2021 3:59 pm
- mikeysklar
- Posts: 14182
- Joined: Mon Aug 01, 2016 8:10 pm
Re: Adafruit Universal Thermocouple Amplifier MAX31856
Hi Erik,
It sounds like you have things connected correctly and are getting a result outside our expected range for this amp. That is to be expected when you are so close the extreme end of the range. More here in the FAQ.
https://learn.adafruit.com/calibrating- ... earization
It sounds like you have things connected correctly and are getting a result outside our expected range for this amp. That is to be expected when you are so close the extreme end of the range. More here in the FAQ.
Code: Select all
At extremely high or low temperatures, the measurements are not correct
The 31855 chip handles the linear range of the K-type thermocouples very well. It does not provide correction for the non-linearities that occur at the extremes of the measurement range. Thermocouple linearization for temperature extremes requires some curve fitting. See this guide for more information and example code:
- ericson95
- Posts: 12
- Joined: Tue Jun 01, 2021 3:59 pm
Re: Adafruit Universal Thermocouple Amplifier MAX31856
Hi Mikey,
thank you for your help.
Yesterday I tried the thermo sensor a second time and it showed me -174°C on the screen. This is also not the correct temperature. The thing is, I bought this one, because on the website they are saying it works good until -210 °C and my used temperature is -196°C... so normally it should work.
Is there a way to calibrate the thermo sensor?
Or is there a other good one from Adafruit, which I could use?
thank you for your help.
Yesterday I tried the thermo sensor a second time and it showed me -174°C on the screen. This is also not the correct temperature. The thing is, I bought this one, because on the website they are saying it works good until -210 °C and my used temperature is -196°C... so normally it should work.
Is there a way to calibrate the thermo sensor?
Or is there a other good one from Adafruit, which I could use?
- mikeysklar
- Posts: 14182
- Joined: Mon Aug 01, 2016 8:10 pm
Re: Adafruit Universal Thermocouple Amplifier MAX31856
We don't have a pre-calibrated ready to go unit that will work so close to the extremes. You will need to use the link in my previous reply to setup the linear handling and do your own confirmation calibrations.
- ericson95
- Posts: 12
- Joined: Tue Jun 01, 2021 3:59 pm
Re: Adafruit Universal Thermocouple Amplifier MAX31856
Okay. Thank you very much...that looks really difficult for a beginner, is there a way to get help in coding? I use a Type T, is it possible to use the same script from the Type K?
- mikeysklar
- Posts: 14182
- Joined: Mon Aug 01, 2016 8:10 pm
Re: Adafruit Universal Thermocouple Amplifier MAX31856
No the tables will be different for type-K vs type-T.
Since you know you are dealing with extremely low temperatures in a very specific range you can use these tables and write your own code to respond to voltage in the specific ranges you are work with.
https://www.thermocoupleinfo.com/type-t ... couple.htm
Since you know you are dealing with extremely low temperatures in a very specific range you can use these tables and write your own code to respond to voltage in the specific ranges you are work with.
https://www.thermocoupleinfo.com/type-t ... couple.htm
- ericson95
- Posts: 12
- Joined: Tue Jun 01, 2021 3:59 pm
Re: Adafruit Universal Thermocouple Amplifier MAX31856
Thank you Mike!
I will try out the two way calibration first and if it doesn't work I will try out this one.
Have a nice weekend!
I will try out the two way calibration first and if it doesn't work I will try out this one.
Have a nice weekend!
Please be positive and constructive with your questions and comments.