weather sensor help!?!

Hi, Sensirion makes several TEMP/HUMIDITY sensors from $6-$70 depending on the degree of resolution. Ebay carries many: the low end, DHT22 AM2302 Digital Temperature and Humidity Sensor Replace SHT10 SHT11 SHT15 | eBay for $5.58, rated for -40 - +125°C (-40 - +257°F). Just seek SHT[10,11,15,20,21,25,71,75] .

Keith

Yes, I am aware of the DHT22

But as I said I need something that goes WELL BELOW -40

I guess I should clarify, we regularly see temperatures below -50C

and fairly common are temperatures below -55C

Also since our temperature range here is fairly drastic

-55C in winter up to about 25C in the summer, what is the best way to protect a sensor such as these outdoors from precipitation, blowing precipitation (snow) and dew?

I believe this from Measurement Specialists one can do -60, I know that may be just on the edge of acceptable for you but I will keep my eyes open for anything else that may be out there.

Hope this helps

Well, the -60C it is rated for is a lot better than anything else I have run across.

Now I get to research and see if I can find any Arduino libraries out there for it.

Good luck with that,

If there is a library that will read a capacitance value then there is a function to turn that into a RH (%) {RH (%) = -3.4656 10+3*X3+1.0732 10+4*X2-1.0457 10+4*X+3.2459 10+3 With X=(C(read) / C@55%RH)}. I have not worked very much with Arduino but I did find this library and this example.

Hope to hear how your project goes

Hope this helps finding a solution.

.

Just keep in mind that RH stand for relative humidity. If the water in the air (humidity) freeze the RH = 0% in any case. Thus the sensor must just survive the extreme cold condition while RH will be 0%.

  There is also a method of reading RH with a wet and dry temperature sensor if you find it difficult finding a RH sensor to survive the extreme cold condition. Formula for this calculation should be available on the net.

O

The last method mentioned (wet dry). I found more reliable and durable. The capacitive sensors tend to hold up better but need to be re-calibrated from time to time. I have done incubation controllers in the past and experience extreme pain on RH sensors. Land me eventually on the wet dry method.

  But in incubation: By controlling the temperature (dry reading) is held stable there for the RH control were not too difficult and controlled the RH with a fixed offset from “temperature reading (dry reading)” by using the wet reading.

bensmith can you provide a link to this method as it does sound interesting.

Thanks

I am beginning to think that I will just be better off figuring out how to access the airport's weather data. It is about 1/2 mile from me but their temperature readings are consistently 2 to 5 degrees F colder that readings I get here at my house. I blame it on the fact that the airport's weather station is a good 100 yards away from an structure or any form of wind or weather break. I have not yet figured out how to get my ethernet shield to do all the tasks I wish to ask from it, but it seems that sourcing their data from the METAR service will be much more reliable for humidity and wind speed than to implement my own sensors for those variables.

We are getting to the time of year where the weather here is beginning to push the limits of some sensors and if this fall is any indication we could be in for a very wild ride this winter.

Thank you all for the help and for the advise.

I have many other questions but for now I will need to set aside this project for the holidays as I will be leaving this cold place for a still cold but not quite as harsh place at least for a few days.

If I may ask, how far north are you ?