DS18B20 1-Wire Outdoor temperature sensor calibration settings?

[DonZalmrol]

Hi all,

I've installed an outdoor DS18B20 1-Wire sensor for my central heating installation to get a working heating compensation.

With the current weather dropping below 0C, it seems the sensor only gets to -0.125C and not to -3C according to the weather displayed on my phone.
So I figured out I need to calibrate it to get the correct temperature. But what are the correct settings for Input value 1, target value 1 and Input value 2, target value 2?

As a test I used these value to get as close to my current outdoor temperature that I fetch from openweathermap.com

The "Outdoor Temp Feeler" is the new DS18B20 sensor
The "Outdoor temperature" is fetched from openweathermap



Settings I've currently set:


As you can see the values are nearly matched. But I'm worried my correction values are wrong. Anyone else who encountered this?

Thanks!

[maxw]

Why do you think the -3 degree from your iPhone is correct?
Is the iPhone connected to a calibrated temp sensor that is located at the same place as the 1-wire sensor?

The value from OpenWeather Map is not the temperature from your garden, believe me
And please do NOT correct the value from the DS18B20 - the value it delivers is correct within +0.5 and -0.5 degree
that is more then good enough for the use case

The correction you have in your image is plain wrong and nonsense
Input and Target must be exact the same for the Sensor DS18B20

[DonZalmrol]

so then it should be the default 0, 0, 100, 100? Or 0, 0, 100, 125?

If so, then the sensor is not getting below -0.125C... Which could not be the temperature here according to the 2 given sources.
I know it's not the temp of my garden, but it should be the temp reading for the city I live in.

As a test, I'll let the sensor work for the night with statistics enabled.

Thanks for the input!

[maxw]

It has to be 0 ... 0 and 100 ... 100 (or anything similar that is a 1:1 mapping)

And if the Sensor is not defective AND temperature is really below -1° it will deliver -1

It also makes no sense to show more than one decimal digit, as -0.125C might in reality be anything between +0.425 and -0.625 as accuracy is +- 0.5 (worst case)

[DonZalmrol]

Thanks, I'll see what it does tonight. I was a bit focused on the "-0,125C) value and was thinking the sensor wouldn't go below it.

The reason for the correction values came from this post: https://www.loxforum.com/forum/softw...sensore-offset
So I thought I needed to do the same for my sensor...

[Christian Fenzl]

1-Wire DS18B20 are calibrated from factory. No calibration required.
Data transfer is digital, so no “temperature loss” on the wire (different to analog resistance sensors like BT1000).