Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 107250 times)

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Offline dendrite

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Privately owned airport. Not sure who has the right to do what but if it was my property it would be gone.
Well, I guess pilots could just rely on a windsock... ;)
It's ongoing they ignore it so next step is getting city involved.
Who's they? I know the city owns the airport, now the question is who maintains the ASOS? If it's the city, then you're obviously on the right track.
If I were you and you're still not getting satisfaction, I'd give these guys a call and tell them you're concerns. If they can't help, they should be able to tell you who can. GL!
https://www.faa.gov/about/office_org/field_offices/fsdo/?state=NE
Isn't VTN a first order station? Wouldn't that fall under the NWS?

Offline dendrite

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I may be wrong, but I think all ASOS stations up here are handled by NWS GYX. AWOS is maintained by FAA.

Offline ValentineWeather

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Probably we just want it fixed but keeps hitting on deaf ears. Ice doesn't lie or get out of calibration so we know which instruments are off. (THE ASOS)
Randy

Offline CW2274

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Privately owned airport. Not sure who has the right to do what but if it was my property it would be gone.
Well, I guess pilots could just rely on a windsock... ;)
It's ongoing they ignore it so next step is getting city involved.
Who's they? I know the city owns the airport, now the question is who maintains the ASOS? If it's the city, then you're obviously on the right track.
If I were you and you're still not getting satisfaction, I'd give these guys a call and tell them you're concerns. If they can't help, they should be able to tell you who can. GL!
https://www.faa.gov/about/office_org/field_offices/fsdo/?state=NE
Isn't VTN a first order station?
I have no idea what a "first order station" is.

Offline CW2274

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I may be wrong, but I think all ASOS stations up here are handled by NWS GYX. AWOS is maintained by FAA.
The way I understand, ASOS's are NWS/FAA territory and AWOS's are airport management maintained. But as I said a while back on this matter, I'm sure one size doesn't fit all.

Offline dendrite

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Privately owned airport. Not sure who has the right to do what but if it was my property it would be gone.
Well, I guess pilots could just rely on a windsock... ;)
It's ongoing they ignore it so next step is getting city involved.
Who's they? I know the city owns the airport, now the question is who maintains the ASOS? If it's the city, then you're obviously on the right track.
If I were you and you're still not getting satisfaction, I'd give these guys a call and tell them you're concerns. If they can't help, they should be able to tell you who can. GL!
https://www.faa.gov/about/office_org/field_offices/fsdo/?state=NE
Isn't VTN a first order station?
I have no idea what a "first order station" is.
http://www.weather2000.com/1st_order_wbans.txt

Basically your long term climatological sites.

Offline CW2274

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Huh, news to me. Thanks!

Offline ValentineWeather

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Basically your long term climatological sites.

And all of a sudden its +2° high. How surprising  :evil:
Randy

Offline CW2274

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I guess I'll dial back the humidity 2% and see how that looks for now. Crap...
Granted, the air mass has changed little, but taking out 2% has put my 31 in it's wheelhouse because the readings are tracking to the point of astonishment. :shock: Shows how good this sensor should be. Too bad this can't be over the entire 0-100% range.  ](*,)

Offline drew1021

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Our local ASOS went haywire many years ago and stayed that way for years resulting in a +2-3 degree error. Stood out like a sore thumb. Frustrated me to no end. Finally one day out of the blue it was fixed. I inquired about it to the forecast office for our region and was told that a construction project several years before had cut the sensor bundle and never was repaired properly. They had to run a new line. Wala!
VP2 with 24 hour FARS. WU: KNCLEWIS2. CWOP/APRS: DW4712, COCORAHS: NC-FR-7

Offline ValentineWeather

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Who was they? They was forecast office primarily and emails to ASOS aomc@noaa.gov<aomc@noaa.gov>; all ignored.  Went back and looked at some old blogs:

03/04/2018 6:30am update: Fog (freezing) this morning with just below freezing temperatures both East and West side Valentine. ICE has formed on chain link fencing west Valentine with temperature between 31.1 to 31.5°. Airport visitors with ASOS thermometer still running 2 degrees warmer (33.8°) could be in for a surprise. Make sure you deice because the chain link doesn't lie.
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Randy

Offline ValentineWeather

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Our local ASOS went haywire many years ago and stayed that way for years resulting in a +2-3 degree error. Stood out like a sore thumb. Frustrated me to no end. Finally one day out of the blue it was fixed. I inquired about it to the forecast office for our region and was told that a construction project several years before had cut the sensor bundle and never was repaired properly. They had to run a new line. Wala!

Thanks for sharing.
Randy

Offline jerryg

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Wow how can you guys live in that kind of cold? Down here everyone panics and drips pipes and cover plants when the temp gets down to 32 lol. Normally we may get into the twenties a couple of times in a normal winter. I am amazed that the sensor perform at all at those temps. Well let me know this winter when it is getting that cold and i will send you a jar of hot air fresh from the outside.  :lol:

Offline galfert

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Privately owned airport. Not sure who has the right to do what but if it was my property it would be gone.
Well, I guess pilots could just rely on a windsock... ;)
It's ongoing they ignore it so next step is getting city involved.
Who's they? I know the city owns the airport, now the question is who maintains the ASOS? If it's the city, then you're obviously on the right track.
If I were you and you're still not getting satisfaction, I'd give these guys a call and tell them you're concerns. If they can't help, they should be able to tell you who can. GL!
https://www.faa.gov/about/office_org/field_offices/fsdo/?state=NE

Thank you for this contact information. I'm going to contact the Orlando office of the FAA. I've been dealing with a bad ASOS at KORL Orlando Executive Airport reporting bad SLP. You can read what I've been dealing with here.
https://www.wxforum.net/index.php?topic=34821.0
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WU: KFLWINTE111  |  PWSweather: KFLWINTE111
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Windy: pws-f075acbe
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Offline jerryg

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I have always wondered what type of measuring equipment is used when they measure -75 to -100 are colder temps. Most home use temps don't go that low or perform well in the minus ranges. The record cold temp here was 8 degrees and the high was 111 degress, very rare to get into the 100's in the summer and near 20 in the winter so nearly all measuring devices work just fine.
the sht31 temp appears to really be the strong point of the sensor and the humidity the weak point, too bad, could really be a great sensor otherwise.

Offline WheatonRon

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...

the sht31 temp appears to really be the strong point of the sensor and the humidity the weak point, too bad, could really be a great sensor otherwise.

Yes the temperature sensor of the SHT31 is right on. Unfortunately, the humidity if off. Most people, myself included, desire accurate temperature vs. humidity accuracy. Too bad this sensor doesn’t capture both readings correctly and consistently.
Davis VP2 with SHT31 (3 complete VP2 systems—2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline CW2274

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Privately owned airport. Not sure who has the right to do what but if it was my property it would be gone.
Well, I guess pilots could just rely on a windsock... ;)
It's ongoing they ignore it so next step is getting city involved.
Who's they? I know the city owns the airport, now the question is who maintains the ASOS? If it's the city, then you're obviously on the right track.
If I were you and you're still not getting satisfaction, I'd give these guys a call and tell them you're concerns. If they can't help, they should be able to tell you who can. GL!
https://www.faa.gov/about/office_org/field_offices/fsdo/?state=NE

Thank you for this contact information. I'm going to contact the Orlando office of the FAA. I've been dealing with a bad ASOS at KORL Orlando Executive Airport reporting bad SLP. You can read what I've been dealing with here.
https://www.wxforum.net/index.php?topic=34821.0
If I may, lemme give you a little piece of advice; you go in "guns a blazing", they'll cut you off like a gangrenous appendage and there ain't squat you can do about it other than call your congressional rep in DC, then GL with that. You go in with "hey, I may have some safety related stuff for you guys", you're more likely to get an audience that will hear you beef. Whether they act upon it or not will be determined by how credible you're deemed, so have your ducks in a row.

Offline CW7491

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...

the sht31 temp appears to really be the strong point of the sensor and the humidity the weak point, too bad, could really be a great sensor otherwise.

Yes the temperature sensor of the SHT31 is right on. Unfortunately, the humidity if off. Most people, myself included, desire accurate temperature vs. humidity accuracy. Too bad this sensor doesn’t capture both readings correctly and consistently.

I know I keep belaboring the point, but based on my experience with the home-brew SHT75 and especially the $17 Acurite SHT31, I’m not convinced this is a Sensirion issue as much as it’s a Davis issue.

Offline WheatonRon

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...

the sht31 temp appears to really be the strong point of the sensor and the humidity the weak point, too bad, could really be a great sensor otherwise.

Yes the temperature sensor of the SHT31 is right on. Unfortunately, the humidity if off. Most people, myself included, desire accurate temperature vs. humidity accuracy. Too bad this sensor doesn’t capture both readings correctly and consistently.

I know I keep belaboring the point, but based on my experience with the home-brew SHT75 and especially the $17 Acurite SHT31, I’m not convinced this is a Sensirion issue as much as it’s a Davis issue.

You may be right. At a minimum, Davis contributed to the problem with poor shipping procedures, etc.
Davis VP2 with SHT31 (3 complete VP2 systems—2 with a daytime fan and 1 that has a 24 hour fan); CWOP--CW5020, FW3075 and FW4350; WU--KILWHEAT17, KILWHEAT36 and KILWHEAT39; WeatherCloud.net; CoCoRaHS--IL-DP-132; and Weatherlink 2.0

Offline ValentineWeather

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Have you guys been watching Jerry's new SHT75 dewpoint vs the airport?
Looks like to me the 75dp is running higher too. I would say on average 2° dp temperature. 
The ASOS is only 8 miles away and recorded high temperature +2° over the SHT75 in passive shield for high yesterday which also seems excessive considering wind was well mixed with average wind speed 14 mph during high temperature period. 
Correction Jerry posted another thread his high temp was 91. Uploads to cwop are spaced so missed the actual high.

Jerry   https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=AT358&unit=0&timetype=LOCAL
ASOS   https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=KVCT

« Last Edit: August 06, 2018, 05:34:26 AM by ValentineWeather »
Randy

Offline ValentineWeather

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...

the sht31 temp appears to really be the strong point of the sensor and the humidity the weak point, too bad, could really be a great sensor otherwise.

Yes the temperature sensor of the SHT31 is right on. Unfortunately, the humidity if off. Most people, myself included, desire accurate temperature vs. humidity accuracy. Too bad this sensor doesn’t capture both readings correctly and consistently.

I know I keep belaboring the point, but based on my experience with the home-brew SHT75 and especially the $17 Acurite SHT31, I’m not convinced this is a Sensirion issue as much as it’s a Davis issue.

So the 75 is running lower DP for sure?
Good to know I have a couple coming. Was wondering watching Jerry's.
The Acurite runs 5% lower humidity during the daytime and still manages to hit 98% in mornings like today when my almost new Davis SHT31 seems to be stuck at 97% now.
Randy

Offline drew1021

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Just a thought, I wonder if Davis is purchasing 31's that don't make the cut at a reduced price.
No proof, just wondering.
VP2 with 24 hour FARS. WU: KNCLEWIS2. CWOP/APRS: DW4712, COCORAHS: NC-FR-7

Offline CW7491

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...

the sht31 temp appears to really be the strong point of the sensor and the humidity the weak point, too bad, could really be a great sensor otherwise.

Yes the temperature sensor of the SHT31 is right on. Unfortunately, the humidity if off. Most people, myself included, desire accurate temperature vs. humidity accuracy. Too bad this sensor doesn’t capture both readings correctly and consistently.

I know I keep belaboring the point, but based on my experience with the home-brew SHT75 and especially the $17 Acurite SHT31, I’m not convinced this is a Sensirion issue as much as it’s a Davis issue.

So the 75 is running lower DP for sure?
Good to know I have a couple coming. Was wondering watching Jerry's.
The Acurite runs 5% lower humidity during the daytime and still manages to hit 98% in mornings like today when my almost new Davis SHT31 seems to be stuck at 97% now.

Yes, in my experience the 75 runs lower than the Davis 31. By about 1-2F in DP on average. That’s not to say there is no wet bias at all particularly after periods of prolonged high humidity as outlined in the data sheet. But it tends to “dry out” more quickly. The Acurite 31 seems to be superior to the 75 in the little bit of side by side I’ve done with the Davis 31. Consistently 3-5% lower RH as I think you’ve said you’ve seen. Temp is right on. Of course it hasn’t been exposed to prolonged periods of high humidity either.

Offline dendrite

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Have you guys been watching Jerry's new SHT75 dewpoint vs the airport?
Looks like to me the 75dp is running higher too. I would say on average 2° dp temperature. 
The ASOS is only 8 miles away and recorded high temperature +2° over the SHT75 in passive shield for high yesterday which also seems excessive considering wind was well mixed with average wind speed 14 mph during high temperature period. 
Correction Jerry posted another thread his high temp was 91. Uploads to cwop are spaced so missed the actual high.

Jerry   https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=AT358&unit=0&timetype=LOCAL
ASOS   https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=KVCT
I've been following him on surface maps for a few days and he seems to be pretty close to what you'd expect being between VCT and the more humid PKV. You can see his dewpoint fluctuate depending on the component of onshore flow when the moisture boundary is between those 2 METAR sites.

Man, you tell me not to compare to other stations and then you do it. (just kidding around) ;)

Offline jerryg

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Well i got a chance to test out a theory this morning, the sun made it out for a short period and the winds were light. I suspected for some time that in high humidity areas like mine the fan running at night gets the interior of the shield wet and causing a lag in temp and humidity readings in the am. When looking at the cwop info it showed the temp lagging rising in the am and the humidity slow to go down. I put the fars fan on the photocell set up i have so the fan was off at night and on at daylight. This morning the fars temp and humidity followed the two shields right off the bat, no delay at all. The temp was slightly higher and the humidity was two percent lower in the fars with the fan off all night but when the fan came on the temp and humidity read the same as the other two. Now if i get this result everytime it will show that the sensors are in a very damp chamber during the night and causing errors in the am until it dries out. This is a test, only a test lol.

 

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