Temperature Sensor, 0.1 degree precison

[Martin]

Hello everybody,

I would like to measure temperature in the area of -30 to +30 with a precision of 0.1 degree.
If my thermometer shows 22.5, is should be 22. 5, neither 23 nor 21.5.
What is the best way to get this precision at Arduino?
DHT22. Hm.
DB18B20 - not bad, but precision is not there, +-0.5 degrees.
HDC1000. hm.
BME280 on a break out board: All for a toss.
Maybe, somebody soldered it a bit too tough and against specification on the board.
In the area of 10 to 26 degrees, I'm getting results scattered across 6 degrees.
The sensor OK at 10 C, did not deliver properly at 25 C.
My best results i obtained with NTCs. I have 3 different ones (10K, 20K, 100 K Ohm), and they scatter a little only from each other. What is great, when I compare this to other couples of sensors.
However, taking into account the precision of the NTC and series resistor and the ADC resolution of Arduino, I do not think I'll ready for a clear .1 degree precision.

What is the best way to get precision of 0.1 degrees?

Thanks!
Martin

[m26872]

@Martin I have a MAX31865 and Pt100 class B on my desk ready to achive this. Project has been on my list for some time but Arduino lib and examples are found on the internet.

[korttoma]

Is it not possible to change the resolution on the DS18B20? Seems like 9 bit (0.5 degrees) resolution is used by default but this can be changed. However the accuracy is still +-0.5 degrees.

If someone knows how to change the resolution, please comment.

Is it as easy as following?:

sensors.setResolution(10);  //Set resolution to 10 BIT

[korttoma]

Replying to my own question. Found this thread:

http://forum.mysensors.org/topic/2686/improve-ds18b20-resolution/6

[Martin]

Hi,

I already was lurking towards PT100, but afraid of the effort - The Wheatstone bridge, the Operational Amplifiers. All has to be precisely set up, probably equal or better as 0.1% to get finally the accuracy of 0.1 C.

So - thanks for the hint to MAX31865. It reduces effort remarkably!

Martin

[m26872]

@Martin You're welcome! Please share it with the rest of us if you make the first MySensors sensor with this.

[scalz]

Hi!

if it can help..
https://github.com/hallard/MAX31865-Breakout
https://github.com/hallard/arduino-max31865