My ds18b20 is off (lower) by 3 to 5 °F randomly
The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements
Official proper DS18B20 are calibrated at source, they still have the ±0.5°C Accuracy you mention.pcmanbob wrote: ↑Mon May 13, 2019 12:33 pmWell no temperature sensor is 100% accurate unless its been calibrated against a known good / calibrated thermometer.
The DS18B20 has an accuracy of ±0.5°C Accuracy from -10°C to +85°C, but its still possible yours might be outside the error range depending were you got them from there of lots of rejects for sale on the web.
Boiling water and ice in distilled water, compensate for your altitude, there are online calculators.
Hello,omegaman477 wrote: ↑Mon May 13, 2019 5:43 pmBoiling water and ice in distilled water, compensate for your altitude, there are online calculators.
But I would bet your only reading the top 9 bits and calculating against that, rather than the full 12. Or you have the two 'bytes' assembled in the wrong order.
JohnsUPS wrote: ↑Wed May 15, 2019 1:18 amI have had this happen to me also.
Where were the sensors purchased?
I have about 30 of these sensors. 10 each were purchased from three different vendors. Two of the vendors were of Chinese origin, and the other was Mouser.
After the first order of 10, I realized they were not calibrated because they were not tracking each other to within the published specs - they should have at least tracked within about 1 deg C of each other. So, I ordered another 10 from a different Chinese vendor - same result - differing readings. Finally decided to spend a buck more per sensor and ordered some from Mouser (Digi-Key would also source directly from Dallas/Maxim). All of these sensors tracked each other perfectly - I recall it was much better than half a degree C. Not having any other temperature references handy (that were as accurate) for absolute comparison, I trusted that the Maxim sensors were in calibration partially because they all tracked each other so well.
The Chinese temperature sensors were all out of calibration (compared to the Maxim parts), and one was off by about 3 degrees C. I had six of the "bad" sensors in parallel, mounted next to each other in a row, so they all saw the same ambient temperature and source voltage, but the readings varied. Readings were consistent up or down depending on the room temperature, but all offset from one sensor to the next. The good sensors were deployed with a project I had going on at the time. To possibly get some use from the counterfeit sensors, I calculated offsets. I averaged the readings from four known good sensors (the "calibration standard") compared to one "bad" one. All wired in parallel and very close in physical proximity in order to calculate offsets for the bad sensors.
I would recommend that when it comes to these sensors, source from a reputable vendor and save some heartburn.