The weather station market is so small that companies are not going to manufacture a humidity sensor with specs just for weather stations. Most humidity sensors are designed for indoor use. One of their biggest uses is for HVAC duct testing. That includes the Sensirion sensors.
As I said earlier in the thread, the SHT-31 was not designed for meteorological use and that should be obvious by its limited normal operating temperature and humidity ranges. But those limited operating ranges are normal for humidity sensors because again, they are not designed for meteorological applications. Davis must have felt that this was the best sensor to do the job even though it was not designed for meteorological applications.
I only know of one humidity sensor that is designed for meteorological applications. That is the one I use at home, the Vaisala HMT337. From the Vaisala literature it states:
HMT337 Configurations
Vaisala HUMICAP Humidity and Temperature Transmitter
HMT337 is ideal for the most demanding process and meteorological measurements in high-humidity condensing environments.
It is a rock solid sensor across the board. If Davis were to use it in the VP2 the cost of the station would probably double.
I got some PM's about this comment so let me clarify. Manufacturers don't design humidity sensors specifically for weather stations. However, they will often say their sensor is ideal for weather station use. Then they slap you with the fine print about the normal operating temperature and humidity range and what you can expect if the sensor is subjected to conditions outside those ranges. They are simply saying you can use our sensor in a weather station but don't expect optimal performance outside the normal operating temperature and humidity range. I'm sure Davis tested these sensors thoroughly before shipping them in the VP and concluded that the sensor had acceptable performance outside the sensors normal operating temperature and humidity range. Now what Davis thought was acceptable versus what you are expecting may be two different things
Also, I'm not saying this is the cause of the Davis sensor issue as the problem seems to occur even
within the normal operating temperature and humidity range.
If you have high expectations of a particular weather station then before you buy that weather station, you should read the entire sensor datasheet from the sensor manufacturer. Read them for every single sensor on the weather station to see if it's acceptable to you. Just reading the sensors specifications doesn't tell the whole story.
I like to use the analogy of the webcam, security camera. It's funny how when I shop for a camera and it says "Outdoor Security Camera" (emphasis on outdoor) and then I check the operating specifications and it says operating temperature 4°F to 120°F. Outdoor? Really? Not in a Midwest winter! If you call the manufacturer, they will say, we're not saying you can't use it outside that temperature range. We just don't guarantee optimal performance outside that range and you'll have to try it outside the operating temperature range and see if it's acceptable to you.
Again, I'm not saying this has anything to do with the Davis sensor issue. I'm also not saying there is nothing wrong with the Davis sensor. It's more of a general comment on humidity sensors and why they don't have a wide operating temperature and humidity range when the manufacturer lists "weather stations" as one of their sensors uses.
