Humidity calibration corrections

Thanks, @hlulofs. I see your support ticket and have responded through that route.

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My dewpoint has been wonky for the past week… Taking random huge nosedives for no reason. SmartSelectImage_2018-02-16-19-32-41

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Dew Point is calculated from Humidity. Look at the humidity readings and see if they are off.

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David,

As noted in the feature request thread I would ask the team to consider offering a method to visually change the readings opposed to actually making a offset to the OEM sensor. This way a person could visually see both the OEM vs User Corrected values.

This would ensure a person could always go back to the factory setting because memory is short X months down the road!

Besides sticking the Air into a bag of salt paste solution to mimic a 75% RH or to have a NIST certified instrument not very many people are going to have the ability to say with 100% confidence what the RH really is.

Anyone else’s Air reading high humidity? I have an Air and Vaisala WXT536 both reading humidity in the same area. Air is reading 97%. The WXT536 is reading at 85% and was just calibrated by Vaisala. The other weather stations in my area are also reading in the mid-80s.

Air: https://smartweather.weatherflow.com/station/965
WXT536: https://www.wunderground.com/personal-weather-station/dashboard?ID=KORHOODR9#history

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Joseph, there are a few here that have reported abnormally high readings. David @dsj is aware of the issue and working towards a solution.

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Thanks Gary. I’ll look for an update in future firmware releases. -joe

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In case you missed this post by David;

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Thanks Gary. I did see that, but I didn’t think that note applied to my situation. The weather stations in my area are reading RH in the 80-85% range. Air is reporting 97%. I have it sited under a 4 foot overhang that is dry.

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I would bring it inside and see if the humidity starts to drop. Put it in a area that’s is very dry and see how low it reports. Then place it back outside and watch the readings.

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The humidity/dewpoint/wet-bulb issue seems to be a pretty general issue for AIR.

AIR provides three values: station pressure, air temperature and relative humidity. Dewpoint and Wet-Bulb temperatures must be calculated from those three inputs. This ends up being a pretty complex calculation involving temperature, station pressure and computed vapor pressure and saturated vapor pressure.

For field calibrations, the trusty sling-psychrometer (or a motorized, fan-aspirated version thereof) is the most straightforward and simplest way to determine air temperature and wet-bulb temperature. Those two values, along with station pressure provide a (still complicated) way to compute relative humidity.

But that still leaves the question of where any error is coming from. Is AIR station pressure correct, is AIR temperature correct, is AIR humidity correct? And which value should be adjusted to compensate for any errors?

Sorry for this long message, but I am also still struggling with the humidity/dewpoint/wet-bulb issue here myself. I have moved the AIR unit around until I found a nano-climate that gives me at least passable results. I have compared AIR values (outdoors) with my trusted, well-calibrated sling-psychrometer and found very close matches (remembering that AIR wet-bulb is a computed, not measured, value). But I still have too-frequent occurrences of AIR reporting 100% humidity when my many years of weather observing instincts tell me that humidity is not 100%.

My next tests will be to bring the AIR unit in to a closed room and after a reasonable time to acclimate the instrument, compare it against my three other instruments. Then move it to a room with a rather different humidity and repeat the test. Maybe all of that will provide me with more insight into the issue.

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Air: Temp: 42.8F, Pressure: 29.75 in., Humidity: 98%
Vaisala WXT536: Temp: 42,3F, Pressure: 29.71 in., Humidity: 86%

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My dewpoint and humidity now read 0 …which is obviously incorrect. SmartSelectImage_2018-02-17-23-34-16

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As mentioned by David, there is a calibration solution in the pipeline to allow us to manually change it. Though I have the feeling it is not always the reason behind the errors … Post just above this one can’t be explained by a miscalibrated humidity sensor …
@nwwebb running what firmwares (that’s a question I ask for the @staff) as it might give some insight
Since we just jumped a few versions for hub … and coincidence or not ?? … I see more returns on this subject then before.

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My firmware revision for the AIR is 20…for the hub is 17.

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If the readings are still wrong, reset the Air by opening the battery door for a few seconds.

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My humidity and dew point readings are clearly wrongimage

Can anyone help me?

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There are two factors at play here: One is the sensor overflow issue (which is fixed in a newer version of firmware). The other contributor may be an RH sensor that needs a calibration adjustment.

We’re about to update firmware for everyone from v17 to v35. Once that’s done, I’ll contact you each directly, to work through any remaining issues with your RH sensor.

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My Hub updated to v35 about three minutes ago.

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Seems to be at least 3 separate issues with RH. The microclimate issue surrounding how to cite your device so that it is representative, the issue with the wonky readings related to the a firmware problem and then a problem with calibration on some subset of the devices. I know in my case, a calibration adjustment absolutely did the trick with dew point readings now exactly reflecting nearby airport stations etc in a variety of weather situations including when at or just under saturated conditions. so very pleased that the RH problem was resolved. Good luck to everyone else that still has an issue.

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