Humidity Appears Incorrect

Is anyone else having dew point and humidity measurements? I have two weather stations within 8 miles of me. The temperature at either station and my Smart Weather station never varies more than a degree or two. Both the dew point and the humidity measurement from my station to the other two is a full 10 points higher. This morning the humidity was measuring at 100% and it was partly cloudy and dry. Thanks.

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I found that the humidity from my AIR was about 7% too high
(which means its gets pegged at 100% if above 93%)
you can get a firmware update to fix this (well at least I did :slight_smile: )

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Gary, how do I calibrate the humidity. I was under the impression that the unit came pre-calibrated.

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Hi. We’ve studied the humidity “issue” to great extent and have come to the general conclusion that AIR is actually measuring humidity accurately, and the difference between a typical roof-mounted station versus a normal shaded-closer-to-the-ground AIR siting is to be expected as reality. As you may surmise, it really boils down to siting and what you are trying to measure. If you wish to match the humidity of other stations in your area, site the AIR in the same way (usually in a rad shield mounted up on rooftop). If you wish to measure the data where you physically spend time (ie. Your backyard at 4ft off the ground)…that will typically result in different data. But, you probably already know all this stuff.

Here’s an ongoing comparison from two reporting stations located at the same house.
https://smartweather.weatherflow.com/share/1531/grid – the AIR at this station is located in full shade on south side of house, 4ft up off a tiled porch with decent breeze exposure.
https://smartweather.weatherflow.com/share/1934/grid – the AIR at this station is literally 32 feet away on the north side of the house, full shade 3ft up off wood deck with surrounding landscaping and somewhat limited breeze exposure.

Despite being only 32 feet apart, the humidity readings usually differ by 10%+. When both AIRs are placed in the exact same location, the humidity readings normalize to identical values suggesting that the sensors are working just fine. We also used a sling psychrometer to measure the humidity in each siting and found it to be spot on with the AIR data. Further, when you hang out on the north side of the house it actually feels much cooler compared to the south side…which is reflected in the data.

We often debate the “right” thing to do when it comes to advising customer siting. On one hand, we want normalized data. On the other, users want to know the exact conditions in their exact location. Not sure which is right. What are your thoughts?

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for me, my sensor was in a stevenson screen
next to a Davis sensor
it was reading too high
and that was also the same too high reading compared to a local airport Metar reading
note, I am comparing dew points here, that is what you need to be comparing
(which is derived from temperature and humidity…humidity is only relative, there is no point in trying to compare humidity readings)

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@walter.w.casey, your humidity sensor was calibrated before being shipped. In most cases, your sensor is reading accurately and @WFstaff’s post applies. That said, we will be offering a field calibration feature in the future that will allow you to apply a local calibration on top of the factory calibration. This feature should be used with caution, of course, and only after confirming that it is truly necessary.

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Is there an approximate time when calibration feature will be added? My sensor is in a ventilated screen and is 13% high verified with a motorized psychrometer. A friend of mine nearby me I verified his air, at 15% high. Both of our sensors peg at 100% any time actual humidity is above 85-87%. My thoughts are siting will cause different readings from site to site but 98,99,100% humidity does not happen very often. Just because its raining and everything is wet does not mean 100% humidity. I can go to the WU site and find weatherflow stations just by picking stations that are reporting 100% humidity.

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I’ve also felt like the RH was reading too high, although I don’t have a comparison instrument. The site is in Hood River, Oregon. While that is a rainy location, having RH pegged at 100% for many days at a time seems odd. However, in the last couple of weeks the RH behavior has been much more realistic. I believe we did a firmware update at that time, but not sure if RH was part of that change.

See wx.sugartechllc.com:3000/dashboard/db/1-rebecca?refresh=1m&orgId=1&from=now-80d&to=now.

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“off topic thats is one of the best dashboard implementations of weatherflow data i have seen…congratulations.” http://wx.sugartechllc.com:3000/dashboard/db/1-rebecca?refresh=1m&orgId=1&from=now-80d&to=now

i certainly believe the position of 100% shade is going to have an effect (high humidity readings) during winter,damp months but the reality is that is the actual RH of the area it is positioned.mine north facing it sees no sunlight during winter months and its a rather damp balcony cold area throughout winter i expect it to become totally reversed during the dry longer periods of the summer months .

what i did was put it indoors for few days as our salon during the winter months in radiator heated and the humidity is relatively sub 50% most of the time ,its the dry heat from combi radiators ,within a few hours the AIR came down rapidly .

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I wanted to add that I also have had humidity/dewpoint issues from Day 1 as others have reported in a wide variety of weather conditions.

For instance, right now my station has the highest dew point in the State of Michigan by several degrees. It is approximately 10 degrees too high compared to other nearby stations. And when I mention other stations, I am talking about other backyard stations probably under similar siting arrangements rather that just a typical setup at a local airport. You can check for yourself here: https://www.wunderground.com/weather/us/mi/grass-lake/KMIGRASS7

Moving around to various locations did not resolve this issue although I don’t have a radiation shield or a roof location to try. (I may need to obtain one it appears. Current location is in the shade of a pine tree in an otherwise open grass area(with snow on the ground) that gently faces South about 5 feet off the ground.)

It also has the problem of saturating to 100% during rainy conditions which often is unrealistic.

Some kind of ability to calibrate the humidity or to otherwise be able to lower it so that the reading is comparable to other nearby locations would be welcome. Thank you!

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Humidity is such a localized condition it’s difficult to know which station accuratly shows a correct value.

Here are stations near me and as you can see some of the values are ridiculous.
Screenshot_20180214-120542

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There is a difference between an accurate high humidity level due to a micro climate were your sensor is, and a inaccurate high reading causing your reading to peg at 100% anytime the actual reading is below 100%. This morning my air was 100%,my other sensor 97%.My other sensor does reads 100% sometimes usually when there is fog. As the day progressed my other sensor came down along with other stations near me until they read around 85-87%. Thats when my air came down to 99% at 1:00 pm.
Also if you observe readings from your nearby stations for awhile you can figure out the ones that are good or bad. For an example, temp spikes up fast soon as sun comes up then goes down a little before settling out. Station not shielded from morning sun.

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I simply don’t buy the explanation about the sensor simply being representative of the local microclimate. I have used another dewpoint device and placed it next to my WeatherFlow device and came up with similar readings to other weather stations nearby which all show lower dewpoints all the time in any weather condition except when all locations are fully saturated. Only conclusion to draw is the humidity sensor is defective or it has some other type of software/firm ware issue.

Note: I think will try another suggestion…bring the sensor indoors for a few days to hopefully reset things in case something is water logged. I will report back if successful.

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I don’t buy the micro climate explanation either, but thats what weather flow has been telling me since I first brought up the issue of my
high humidity back in Oct. What I was saying is if your reading high humidity and its accurate, then all other sites will be close. My air is 13% high
so 87% and above I’m pegged. Its a calibration issue. Ive looked at the readings at lots of sites with air and there always high and are pegged at 100% sometimes for days. They say there coming out with a self calibration/offset feature for the app but i can’t get an answer or when.

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You’re right, micro-climate is not always the issue. In many (most?) cases, a high humidity reading can be traced to a siting issue. However, RH is tricky to measure especially when it gets close to 100%. The capacitive type of sensor we use (the same type Davis and others use) is notoriously less accurate near the extremes ends of RH (<10%, >90%). On top of that, the calibration can drift when exposed to extended periods near extreme wet or extreme dry conditions.

Finally, you’re right: it could be a hardware or software issue. There are only about 1000 AIR devices out there and they’ve only been in the field for a few months. We are learning new things every day. It’s possible there is a software or factory calibration issue affecting all or most units out there. We are directing resources at figuring that out right now. If there’s a systemic problem, we’ll figure it out and correct it!

Meanwhile, if you’ve confirmed a discrepancy with your RH sensor using trusted equipment, you may need to adjust the calibration. We are working to enable a field calibration feature soon. Meanwhile, if you have an extreme case, please contact me directly.

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Thanks for the response, and I fully understand the issue. I also realize you guys are working
on many bugs a fixes plus the sky. I’m now assured you are working on fix for this issue and
I can deal with what is going on until fix is complete.
Thanks again.

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“We are working to enable a field calibration feature soon.”

Great! I suspect that will fix the problem as the sensor in my case seems to be consistently high by some factor which suggests a simple calibration should do the trick.

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I believe thats all I need, and my readings will be perfect.

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for me the humidity reading is accurate, because the humidity reach 100% just in the fog condition, even when I have rain in my location the humidity swinging between 85-88%, so I think my station reading is accurate so far.

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David,

Thanks for the update…about an hour ago (before reading your thread) I sent a message to WeatherFlow Support regarding this very issue and included screen shots. I am glad to see you are working on a solution as I do think there is some kind of problem going on. I have included my message to the support folks below. Keep up the great work on this project!

Hendricus

“I continue to see dew point readings that do not make meteorological sense and are just too high. I have included screen shots of both my WF station and my NetAtmo station. The are located within 24 inches of each other. There is no way I should have had an RH of 100% today…all day long. No fog/no rain. The Netatmo reading correspond to all of the neighboring readings I see…no site has readings similar to the WF station. I love everything about the WF station except that the dewpoint has looked off from day one. Might I have a defective dew point sensor? Updated to add an image showing the location of the 2 weather sensors.”

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