How to differentiate between SHT31 and SHT35

Hardware
1

I just received an order of SHT temp/humidity sensors from here:

I had ordered one SHT31 and one SHT35 to test. When I ordered them I distinctly remember from the above link that they would come on a different board with markings as to if each one is SHT31 or SHT35. I’ve just received them and both sensors are on the same purple board which only reads SHT3x. The vendor’s link has also changed and I see that all SHTx sensors now are supposedly on the same board with only SHTx markings.
Of course I now worry that I have just 2 SHT30 sensors :grinning: Is there a way to know which is which? I haven’t powered them yet, but from a first look they are identical.

2

As far as I know, they’re electronically identical and only differ in terms or precision, repeatability, etc.

That said, there’s an almost 100% chance that you have neither of those. What you have is a cloned copy of the SHT3x platform with pretty much random specs anyway. So in a sense, it doesn’t really matter which clone it is, because the clones are all the same anyway :slight_smile: The official specs from Sensirion are not applicable to clones and you will have to manually calibrate it either way.

If you want the real thing, buy from Adafruit, Sparkfun, Mouser or another reputable source.

3

Thanks for the answer. Where I live it’s a little hard to shop from these vendors. How can you be so sure that they are clones? I’d assume both are just SHT30. The weird thing is that in a LOT of places I research the “SHTx” nomenclature is used very often, which is well… a recipe for these kind of things.

4

Well, that’s just how things are. An overwhelmingly large percentage of electronics bought directly from Chinese vendors use counterfeit components. Especially for electronically simple components like the SHT sensors, these are so massively counterfeit that the chance of it being genuine is close to zero, unless you buy from an official distributor of the manufacturer. It’s becoming more and more of a problem, not only for hobbyists, but for the industry at large. But you know, you get what you pay for :slight_smile:

SHT3x is the official nomenclature of the platform. Look at the official spec sheet. Basically what happens is that they’re all produced on the same manufacturing line and then they’re binned into the individual product codes (SHT30, 31, etc) according to their precision tolerances that are measured after manufacturing. For clones, they don’t care about precision, so they all get binned into the same SHT3x category. Sometimes an actual (random) label like SHT31 is printed on them for good measure.

Essentially, if you buy stuff like that from Ali, Banggood or similar, just assume it’s a random sensor with random specs that you will need to calibrate.

5

I’m just in the process of calibrating two “SHT31” sensors I bought on AE. Here are my results so far:

#              - 36.51 -> 32.84  # MgCl2
#              - 45.515 -> 43.20  # K2Co3
#              - 76.45 -> 64.60  # NaNO2
#              - 85.50 -> 84.08  # KCl, not yet stabilized
#              - 100 -> 97.5  # K2SO4

I’m not sure if the NaNO2 somehow messes up with the sensor. It’s also pretty clear that they cap out at 97%. I tested with Licl (11% rh), but abandoned the test thinking there’s something wrong with the salt.