Electronic – Which one of these DS18B20 temperature sensors is fake


A while back I bought two DS18B20 for half price, and today I bought another one for double the price. The part number on the cheaper one is printed while on the expensive one it's laser etched:

On the left is the expensive one.

Even though the price was double, the readings that I'm getting using Arduino are the same:

Sensor1 is the expensive one. While the temperature on mercury thermometer was 23.9-ish degrees.

So what's the difference? Why is the build quality and price different but the temperature readings are the same?

Best Answer

There isn't any good way to know. As Elliot Alderson rightly points out, both could be legitimate, or both could be fake.

  • If the packaging and marking are different between the two parts, that could simply be because the manufacturer changed their packaging process. You'd have to check product change notices to confirm.
  • The price difference could simply be because "each vendor charged the highest amount they could get away with". (The fact that you bought the parts indicates that this strategy worked.)
  • Again from Elliot Alderson, the only way you can really trust a part is if you trust the supply chain. Otherwise the part could be counterfeit, or even if it's not counterfeit it could have been subjected to poor handling practices or similar. It sounds like the supply chain wasn't trusted in either of these cases, so each part should only be trusted to the degree that you have tested it.

Here is a nice presentation from Xtreme Semiconductor, a company that specializes in detecting counterfeit parts. Slides 20-31 show some examples of the tricks people pull when making counterfeit parts. Some are easy to detect with the unaided eye, others require advanced tricks like X-ray or opening up the part, as shown in the same slide set. Probably not something you're looking to do here.

tl;dr Just because the parts look different and were priced differently doesn't necessarily mean that one is good and/or one is fake. Put the part through rigorous testing, or just buy a new part from a trusted source.