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Topic: Thermistor 10K ohms with arduino (Read 107 times) previous topic - next topic


Hi Experts;

Thank you for reading;

I am working on the floor heating systems using 10k ohms thermistor analog reading with UNO R3+ Ethernet Shield 2; I have very peculiar problem with the sensors which are already installed under the floor with the heating system, the analog values are getting changed up and down drastically within few seconds in a condition of  without turning on the heater, whereas the problem disappears when I connect the standalone sensor separately (just outside) and it works great without any problem.
The power fed to the UNO is 12V. One thing was noted during test with existing floor sensor, when I remove the eth shield 2 the analog values are coming proper otherwise improper value (467,435,501,554,468 ….) but with standalone sensor with the shield working properly; I am really confused;
Kindly advise me how to overcome this issue.
Thanks in advance


Do I understand that correctly? You try with the identical sketch (no single character changed) and with a second sensor of identical model (but otherwise identical circuitry) and you get different behavior if the Ethernet Shield 2 is connected?

If you cannot answer all above with a clear yes, you should check your hardware. It's critical that the only thing you change in that setup is the sensor and absolutely nothing else.
If you must change anything else or use another model of thermistor: Post a complete wiring diagram!


Noise from mains power may cause such.
Try add a capasitor  at the analog input.


A 10k (PTC) thermistor is commonly used in underfloor heating applications.
Have you done the basics to check that it is 10k and whether PTC or NTC? It will only be 10k at a specific temperature.
If the thermistor is embedded in the floor covering (tiles etc.) you could have a problem.
The commercial UFH systems use a floor sensor to either control the floor temperature or act as an upper temperature limit sensor - some systems use an air temperature thermistor to control the temperature and a floor sensor to act as a safety cut-out.
Are you using a commercial thermistor or trying to use one of your own? Actually, a homebrew thermistor can be better as you will get the full data sheet with the response curve.
I would try your system with a known thermistor in circuit before embarking on complexities like Ethernet shields.
Be aware that commercial systems use thermistors for cheapness and that there are much better temperature sensors available in analogue form like LM35 or digital DS18B20

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