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Graph of actual performance of fake DS18B20 #17
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...and thanks for sharing that the -00-80s were still around in 2019. |
I looked up the vendor's page on eBay. They still have over 900 in stock if you are keen to buy! |
I should have known better, but the inside of the 'waterproof sensor' exceeded my lowest expectations. I advise anyone looking for DS18B20 sensors not to buy them from eBay/China! |
Nice plot! Would you consider adding it the the README? |
@emulti Thanks for the pointer! I believe I've ordered some based on your hints and will follow up when I receive them. @heitorPB Got to think about it. While I agree that their performance is garbage they seem to be old stock from a European distributor if I understood @emulti correctly, i.e. they perform much worse than the sensors one can expect to get from a Chinese distributor these days. Again, I'll think about it once I manage to buy some. |
To clarify, they were bought direct from an eBay seller in China in 2019, but I didn't get round to using them until this month.
The rubbish build quality of the sensors, slow response due to potting in low grade sealant, when the cable is such cheap rubbish that it is hard to solder- all these things on top of the useless performance mean they were a complete waste of money. We live and learn.
…On August 25, 2020 10:54:32 PM UTC, Chris Petrich ***@***.***> wrote:
@emulti Thanks for the pointer! I believe I've ordered some based on
your hints and will follow up when I receive them.
@heitorPB Got to think about it. While I agree that their performance
is garbage they seem to be old stock from a European distributor if I
understood @emulti correctly, i.e. they perform much worse than the
sensors one can expect to get from a Chinese distributor these days.
Again, I'll think about it once I manage to buy some.
--
You are receiving this because you were mentioned.
Reply to this email directly or view it on GitHub:
#17 (comment)
|
To follow up: the probes I received today contain Family B2 sensors. |
Hi,
Thanks for highlighting this fake sensor issue!
Unfortunately I found out about it after I wasted my money on a bunch of waterproof "DS18B20" sensors on eBay in 2019.
The ROM codes are of the form 28-tt-tt-43-xx-00-80-crc.
To highlight just how useless (and potentially dangerous if used in a temperature control system) these fakes are, have a look at this graph of the temperature output at 12 bits resolution from five sensors at identical temperature. There are four fakes, and one genuine item. Temperatures are being read using the standard DallasTemperature library on an Arduino.
You only get one guess which is the genuine one...
One genuine, four fake DS18B20
Building a precise temperature control system is practically impossible with this garbage. The readings vary randomly by so much, and in an asymmetric way, that even by applying heavy smoothing they are neither accurate to within a degree, or stable. The response time of the smoothing loop becomes uselessly slow for many applications.
Chris
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