ESP8266 with DS18B20 irregular readings

Other Hardware Sensors
1

Good morning,

I'm using the ESP01 and I put the ds18b20 with its 4.7K resistance but I detect too high measurements.
I also tried with 2.2k resistors but the same.

Even a sensor has 10 degrees more ...

I thought, ok I know that it reads n degrees more and therefore I lower the reading from the code but I have calibrated the sensors to 21 degrees and when I have placed them I always have very wrong readings.
In the bedroom I have 17 degrees (beds with 2 temporary programmable thermostats) and I have 19 degrees on the right ...
I tried to calibrate them on the spot, that is in the relative room but then they are always wrong.
In the room when I heat the temperature increases but is always lower than that read by the external Chrono. For example, if it reaches 20 degrees the ds always marks me something less ...
In the bathroom he tells me that I am 19.11 degrees and even if I warm I see the temperature that also goes to 22/23 degrees with 2 external digital thermometers but the ds gives me a maximum of 19.38 ....

What am I doing wrong?

2

Hi @abinformatica,

You purchased your 18B20 from a trusted supplier.
Many low quality fake 18B20s have appeared on the market.

RV mineirin

3

I bought this on Amazon 5 pcs at 7,99€

4

For more information than you may care to know about DS18B20 sensors see

5

I believe mine are counterfeit. I have now ordered from RS Online.

Thanks

6

Some non Maxim ones are better than others. I bought some probes on Aliexpress that turned out to be his B2 type. They are within .5C when compared to a platinum RTS of known accuracy.

7

Updates:
I ordered the sensors from RS Online, a 40in euro 5 sensors.
Now I am doing tests and I have more or less the same results, that is, as soon as I connect the node it gives me a temperature and then slowly rises until it stabilizes after about 5 minutes.
For example, now I have written a code that sends me the data every 30 seconds:
22.06
23.06
23.94
24.75
25.31
25.69
26.13
26.44
26.81
26.94
27.19
27.50
27.50
27.63
27.94
28.00
28.06
28.00
28..06
28.19
28.13
27.75
27.81
28.06
28.19
28.13
28.31
28.25
28.13
28.13
28.00
28.19
28.31
28.19
27.75
27.88
28.06
28.19
28.25
28.31
28.38
28.44
28.38
28.56
28.56
28.63
28.56
28.69
28.81
28.75
28.88
28.88
28.81
28.88
28.88
28.88
28.81
28.75

In short, in my opinion it seems that there is a capacitor that is charging but can it take up to 15/20 minutes?

In addition, the ambient temperature is 20.8C, is it also normal that it marks me 8 degrees higher?

Thanks

8

Updates
After it stabilized (about 2 hours) the DS18B20 measured 30.69C while two other digial thermometers were at 24.00C.
Via code I did t = t-6.6;

And now when there are 24 real degrees it reads 24.12C. And I thought PERFECT!

Then I did another test, I put everything on the outside and it's not good at all.
The DS18B20 reads 4.31C while there are 14.5C

I don't know what to do anymore, I'm desperate!

9

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