0

I am using PT100 (3 Wire) to measure the temperature with Arduino Uno and MAX31865. I have connected everything perfectly. Configuration in the code i am using is :

max1.begin(MAX31865_3WIRE);

And the output is:

output

RTD value: 0 
Ratio = 0.00000000
Resistance = 0.00000000
Temperature = -242.02

I am testing it in a room temperature.

My question is , is there any settings or calibration that i need to do, or any other way to test the PT100 sensor, because the temperature is showing correct readings ?

  • I had the same problem and was solved due to the comment of fshero (Jun 3 at 11:35) about a capacitor wich drops the voltage on PIN 20 of the MAX31865. I have logged in just to highlight the solution. Thanks fshero!! – LeandroIP Aug 19 at 20:06
  • I've the same problem with my shields; Where is the componant to remove on the shield to solve the problem? a picture of the modification is welcome thanks a lot fabien – fabien Sep 27 at 8:27
2

I nearly have the same problem. I use five of the MAX31865-Boards with 2-Wire Termocouples on an Arduino Nano. Two of the five boards are working perfectly. The other 3 boards show exactly the same wrong behaviour you described. My temperature readings are exactly like yours (-242.02).

But I think I found the reason for the not working ones: The two working boards I bought on Amazon. The other three not working boards I bought on AliExpress. Maybe I (and maybe you too) got really bad fakes from China and they are simply dead :(

(BTW: If I remove one working board from the SPI bus and read out the temperature with the arduino, I get also the value of -242.02. This value seems to be an error value in the Adafruit MAX31865 library)

  • I figured out the source of the error in my case: After some "debug measuring" with a multimeter I recognized, that the voltage of the VDD Pin of the Sensor is too low (1.6V but 3.3V are required)! It seems the chinese version has a capacitor at the place, where a originally a filter ferrite should be (see part FB1 at adafruit_products_schem.png). This causes the voltage drop. I removed the capacitor and replaced it with a solder bridge. Et voilá. It's working perfectly! :D – fshero Jun 3 at 11:35
  • If wanted, I can provide some pictures of my modification – fshero Jun 3 at 11:41

protected by Community Sep 27 at 13:20

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.