PT100 Issie / Wrong reading
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PT100 Issie / Wrong reading

by Michel_S on Thu Apr 05, 2018 1:43 am


I bought on the 7th of March in SEMAGEEK in France a PT100 sensor and a MAX31865 module, both from Adafruit. Olivier from Semageek recommended me to discuss my issue on your Forum.

When putting in operation the module and the sensor the informations on the Arduino Terminal where wrong like :
RTD value: 468
Ratio = 0.01428223
Resistance = 6.14135742
Temperature = -228.30
Fault 0x80
RTD High Threshold
After having checked a few things recommended on your forum which did not allow to solve the issue, I decided to put a standard 100_Ohms resistor in place of the PT100. To simulate the 3 wire connection, I have put a strap between F+ and RTD+. And this time the device worked properly as you can see in the message returned by the Arduino terminal :
RTD value: 7418
Ratio = 0.22637939
Resistance = 97.34313964
Temperature = -6.76
When using an Ohmeter the PT100 has a value of about 110_Ohms which seems to be correct at ambiant temperature .

I incriminated then a possible poor connection on the Faston connectors wrapped to the sensor wires. To eliminate this issue I have removed the original connectors and put in place a welded pin. This did not solve the issue when I made a new test with the module.

Thus I concluded that the PT100 sensor may suffer an internal connection issue which would not be visible whis the Ohm-meter but would appear when a much lower current is used to measure the resistance.

Would you please comment.

Posts: 4
Joined: Thu Apr 05, 2018 1:27 am

Re: PT100 Issie / Wrong reading

by semageek on Wed May 02, 2018 3:37 am

Is it possible to have a response for my customer ?
Product : PID 3290 : Platinum RTD Sensor - PT100 - 3 Wire 1 meter long

And move the thread to : Forum Index > Supported Products & Projects > Other Products from Adafruit

Best Regards

Posts: 8
Joined: Thu Jan 09, 2014 6:15 am

Please be positive and constructive with your questions and comments.