Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 30784 times)

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Offline dendrite

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Obs from the Persian Gulf.  A little off topic I know but I seriously wonder if there are any Davis VP2s around here and how they compare to official obs.  I just cant imagine a dew point in the 90's with a HI of 140!  My old boss who was a Weather Officer with the Navy back in the 70's used to tell me about the insane inversions they get there and how it made tacking aircraft with radar very difficult.


This is an Ambient

https://www.wunderground.com/personal-weather-station/dashboard?ID=IABUDHAB125&cm_ven=localwx_pwsdash#history/tdata/s20180813/e20180813/mdaily

93F/90F at one point. No thank you.

Offline dport

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High end humidity update.  I've had my VP2 for 2.5 months now.  The SHT31 seems to be performing great.  I regularly hit 99% humidity and this morning was stuck at 99% for 5 straight hours (no calibration adjustments made at all).  https://www.wunderground.com/personal-weather-station/dashboard?ID=KPABRYNM2#history/tdata/s20180814/e20180814/mdaily

There might be a slight wet bias in the mid ranges, but not much.  Perhaps I just got lucky received a "good" temp/hum sensor.  We shall see if I can continue to hit 99% in the coming months. 

Offline dendrite

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High end humidity update.  I've had my VP2 for 2.5 months now.  The SHT31 seems to be performing great.  I regularly hit 99% humidity and this morning was stuck at 99% for 5 straight hours (no calibration adjustments made at all).  https://www.wunderground.com/personal-weather-station/dashboard?ID=KPABRYNM2#history/tdata/s20180814/e20180814/mdaily

There might be a slight wet bias in the mid ranges, but not much.  Perhaps I just got lucky received a "good" temp/hum sensor.  We shall see if I can continue to hit 99% in the coming months.
I've always noticed mine starts losing the ability to reach upper RH values after the first warm season. Come the following May, 99-100% becomes a max of 97-98%.

Offline hwcorder

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.

     




Offline dendrite

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.
Nice. I like the creativity there. If you had removed the clip from the pen I would've thought it was meant for holding a temp probe.  :grin:

Is that data available online?
« Last Edit: August 14, 2018, 07:09:34 PM by dendrite »

Offline openvista

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Ended up using the connector I was originally going to use.

Which one was that?
« Last Edit: August 14, 2018, 08:32:44 PM by openvista »
Davis Vantage Pro2 FARS | https://marquetteweather.com | EW7933

Offline hwcorder

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.
Nice. I like the creativity there. If you had removed the clip from the pen I would've thought it was meant for holding a temp probe.  :grin:

Is that data available online?

Thanks!  Yes I upload to Wunderground and CWOP.
 https://www.wunderground.com/personal-weather-station/dashboard?ID=KNCBELMO18#history
https://weather.gladstonefamily.net/site/D5686

Ended up using the connector I was originally going to use.

Which one was that?
Here they are. The post are a little more flexible that the other ones so you can spread the pins out some. Not too much though.
https://www.mouser.com/ProductDetail/Harwin/M50-3030442?qs=sGAEpiMZZMs%252bGHln7q6pm8Vn94ktop%2fJmuuS%252b8ZjnXtI6OeGFBMW0g%3d%3d

Offline jgentry

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.
Nice. I like the creativity there. If you had removed the clip from the pen I would've thought it was meant for holding a temp probe.  :grin:

Is that data available online?

Thanks!  Yes I upload to Wunderground and CWOP.
 https://www.wunderground.com/personal-weather-station/dashboard?ID=KNCBELMO18#history
https://weather.gladstonefamily.net/site/D5686

Ended up using the connector I was originally going to use.

Which one was that?
Here they are. The post are a little more flexible that the other ones so you can spread the pins out some. Not too much though.
https://www.mouser.com/ProductDetail/Harwin/M50-3030442?qs=sGAEpiMZZMs%252bGHln7q6pm8Vn94ktop%2fJmuuS%252b8ZjnXtI6OeGFBMW0g%3d%3d

How does the raw readings of the 75 humidity sensor compares to the airport? Why I ask is that you have done some offset stuff on WD.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline hwcorder

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.
Nice. I like the creativity there. If you had removed the clip from the pen I would've thought it was meant for holding a temp probe.  :grin:

Is that data available online?

Thanks!  Yes I upload to Wunderground and CWOP.
 https://www.wunderground.com/personal-weather-station/dashboard?ID=KNCBELMO18#history
https://weather.gladstonefamily.net/site/D5686

Ended up using the connector I was originally going to use.

Which one was that?
Here they are. The post are a little more flexible that the other ones so you can spread the pins out some. Not too much though.
https://www.mouser.com/ProductDetail/Harwin/M50-3030442?qs=sGAEpiMZZMs%252bGHln7q6pm8Vn94ktop%2fJmuuS%252b8ZjnXtI6OeGFBMW0g%3d%3d

How does the raw readings of the 75 humidity sensor compares to the airport? Why I ask is that you have done some offset stuff on WD.

The way I have it done on WD the adjusted readings and the raw readings from the sht75 are the same. But in the high end the raw readings only will reach 97-98% my adjusted reading will go to 100%.  I guess the short answer would be it tracks pretty darn close to local ASOS stations.

Edit: When I say the adjusted and raw readings are the same I meant through the mid ranges <75%.
« Last Edit: August 14, 2018, 10:36:06 PM by hwcorder »

Offline jgentry

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.
Nice. I like the creativity there. If you had removed the clip from the pen I would've thought it was meant for holding a temp probe.  :grin:

Is that data available online?

Thanks!  Yes I upload to Wunderground and CWOP.
 https://www.wunderground.com/personal-weather-station/dashboard?ID=KNCBELMO18#history
https://weather.gladstonefamily.net/site/D5686

Ended up using the connector I was originally going to use.

Which one was that?
Here they are. The post are a little more flexible that the other ones so you can spread the pins out some. Not too much though.
https://www.mouser.com/ProductDetail/Harwin/M50-3030442?qs=sGAEpiMZZMs%252bGHln7q6pm8Vn94ktop%2fJmuuS%252b8ZjnXtI6OeGFBMW0g%3d%3d

How does the raw readings of the 75 humidity sensor compares to the airport? Why I ask is that you have done some offset stuff on WD.

The way I have it done on WD the adjusted readings and the raw readings from the sht75 are the same. But in the high end the raw readings only will reach 97-98% my adjusted reading will go to 100%.  I guess the short answer would be it tracks pretty darn close to local ASOS stations.

Edit: When I say the adjusted and raw readings are the same I meant through the mid ranges <75%.

So how does it do over 75%?  Wet or dry bias?
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline ValentineWeather

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My acurite continues to act like a SHT31 should running 3-5% below Davis daytime and has no problem reaching 99%.
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Randy

Offline jerryg

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Jealous of that temperature, i got 78 degrees this am heading up to upper 90's today.

Offline ValentineWeather

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Jealous of that temperature, i got 78 degrees this am heading up to upper 90's today.

Summers are nice but you pay for it on the other end.. ;) If you don't like cold.
Randy

Offline hwcorder

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So I completed and installed my DIY probe made out of a Pilot Pin.  Obviously the hardest part is getting the wires connected to socket the connector.  I can tell you that those solder cup connectors I ordered from Mouser where no easier to work with and seemed more fragile.  Ended up using the connector I was originally going to use.  After a lot of patience I protected the connections with 4 very small heat sink wraps for each of the 4 wires and then covered that one with a larger wrap that covered the shielded part of the cable to the body of the connector itself.  I then fit the connector through a slot in a piece of pcb board which of cut and shaved into a round piece that would fit into the body of the pin.  All of this was done using a Dremel Tool.  This was all sealed and weatherproofed with hot glue. 

Where the sht75  (and hopefully a future 35) plugs in, fits perfectly into an Viasala HMP60 filter housing. It does not screw in but the fit is quite snug and I doubt anything could get through.  At first I was using the gel grip in the pin to further seal the filter and pin housing but noticed that it was generating static charge so I removed it.  I think filter is very well sealed but I might wrap some electrical tape around it just to be sure.  Here are some pics.  I will say it will be very nice to be able to remove and replace the probe with ease into the MeteoShield Pro which I have decided to use at least for now.
Nice. I like the creativity there. If you had removed the clip from the pen I would've thought it was meant for holding a temp probe.  :grin:

Is that data available online?

Thanks!  Yes I upload to Wunderground and CWOP.
 https://www.wunderground.com/personal-weather-station/dashboard?ID=KNCBELMO18#history
https://weather.gladstonefamily.net/site/D5686

Ended up using the connector I was originally going to use.

Which one was that?
Here they are. The post are a little more flexible that the other ones so you can spread the pins out some. Not too much though.
https://www.mouser.com/ProductDetail/Harwin/M50-3030442?qs=sGAEpiMZZMs%252bGHln7q6pm8Vn94ktop%2fJmuuS%252b8ZjnXtI6OeGFBMW0g%3d%3d

How does the raw readings of the 75 humidity sensor compares to the airport? Why I ask is that you have done some offset stuff on WD.

The way I have it done on WD the adjusted readings and the raw readings from the sht75 are the same. But in the high end the raw readings only will reach 97-98% my adjusted reading will go to 100%.  I guess the short answer would be it tracks pretty darn close to local ASOS stations.

Edit: When I say the adjusted and raw readings are the same I meant through the mid ranges <75%.

So how does it do over 75%?  Wet or dry bias?

I would say it continues to do very well all the way up until the mid 90% range before the dry bias shows up. Sensor seems to peek at 98%.

Offline dendrite

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I would say it continues to do very well all the way up until the mid 90% range before the dry bias shows up. Sensor seems to peek at 98%.
Yeah, I think Davis and Sensirion may be a little at fault here. My new 75 has no problem with 99%-100%, but my 5 y/o one maxes out at 96%. I assume the age of yours is somewhere in between and you're maxing at 98%.

Like you, I find both do well during the day with lower RH.

Offline hwcorder

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I would say it continues to do very well all the way up until the mid 90% range before the dry bias shows up. Sensor seems to peek at 98%.
Yeah, I think Davis and Sensirion may be a little at fault here. My new 75 has no problem with 99%-100%, but my 5 y/o one maxes out at 96%. I assume the age of yours is somewhere in between and you're maxing at 98%.

Like you, I find both do well during the day with lower RH.

I also like the fact that it is quicker to come down from a night of high humidity than the 31.  Something think jerryg also noticed in his tests.

Offline jgentry

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Did you see what Jerry and I ordered?  I have 2 on the way may not be here until fall however. https://www.aliexpress.com/item/2pcs-Waterproof-Temperature-and-humidity-sensor-shell-SHT10-SHT21-SHT15-shT11-sht20-SHT75-sensor-protective-sleeve/32725766858.html?spm=a2g0s.9042311.0.0.69af4c4dlQrpxK

Others have some like https://www.emesystems.com/sht75pg/documents/SHT75PG.pdf

dendrite are there no worries about contamination using silicone conformal coating?

Just been looking at the pics of that thing on aliexpress, I hope it isnít as big as it looks in the picture. Would think it would cause the sensor to lag if itís that big. Hopefully Iím wrong but Iím looking forward to try it out when it gets here.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline jerryg

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Well good news and bad news, i got my order in yesterday and they are not that big but they are not very good. I put one out and it ran 1 degree warmer than it should so ipulled it out and ran some checks with my temp. standard and with just the filter part and not the body it stayed .4 degrees warmer than it should . I held it between my fingers for 5 seconds and it took the temp increase almost 5 minutes to recover from a 1.5 degree increase. Well it is from China and i guess i was hoping for the best. I squeeze the filter and it blew apart, looked like compressed formed paper. But the good news is the body makes a good mount for the sensor, just had to add the sf1 filter to it and i have it running in my main shield right now. I swear i know you can not get anything from China worth a damn, i ordered three break out board with sht15 sensors and nothing but crap, one max humidity at 79 another at 82 and the third minimum was running 7 high total loss. I think they were the rejects from the factory. If it has made in China on it it is pure crap.

Offline Old Tele man

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In my best imitation Forrest Gump voice, "Cheap is, as cheap is."
ē SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB;
ē DBX1 Precision Digital Barograph
ē CWOP: DW6988 - 2 miles NNE of Cortaro, AZ
ē WU - KAZTUCSO202, Countryside

Offline dendrite

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Very thick, prolonged radiation fog this morning. The SHT75 has been at 99% for awhile with a low of 54.2F.

CON has been running 1/4-1/8SM visibility and alternating between a dewpoint depression of 0F and 1F. So with rounding, my hunch is that they're actually around 99% RH in reality. They had a low of 53F.

LCI is coming out of the fog now, but had a similar deal. Mostly 0F, but some 1F dewpoint depressions in the 5 minute obs...probably about 99% RH. They were also 1/8-1/4SM and had a low of 54F.

Offline jgentry

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Very thick, prolonged radiation fog this morning. The SHT75 has been at 99% for awhile with a low of 54.2F.

CON has been running 1/4-1/8SM visibility and alternating between a dewpoint depression of 0F and 1F. So with rounding, my hunch is that they're actually around 99% RH in reality. They had a low of 53F.

LCI is coming out of the fog now, but had a similar deal. Mostly 0F, but some 1F dewpoint depressions in the 5 minute obs...probably about 99% RH. They were also 1/8-1/4SM and had a low of 54F.

Awesome! I opened my package that has the 75 sensor in it and I didnít realize how small that sensor really was. Lol
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline dendrite

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Very thick, prolonged radiation fog this morning. The SHT75 has been at 99% for awhile with a low of 54.2F.

CON has been running 1/4-1/8SM visibility and alternating between a dewpoint depression of 0F and 1F. So with rounding, my hunch is that they're actually around 99% RH in reality. They had a low of 53F.

LCI is coming out of the fog now, but had a similar deal. Mostly 0F, but some 1F dewpoint depressions in the 5 minute obs...probably about 99% RH. They were also 1/8-1/4SM and had a low of 54F.

Awesome! I opened my package that has the 75 sensor in it and I didnít realize how small that sensor really was. Lol
Very small and very responsive. My setup really is like the raw data from an ASOS. I may move my sensor up to a full 2m (6.5ft) to pull it away from the sfc heating as much as possible without going over the 2m mark (40 CFM fan remember). Either that or I'll put a 5 minute averaging algorithm on the data. For now I'm just accepting the raw readings for what they are. If I put my hand briefly under the air intake of the shield I see a spike in temperature in my data.

Offline jgentry

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Very thick, prolonged radiation fog this morning. The SHT75 has been at 99% for awhile with a low of 54.2F.

CON has been running 1/4-1/8SM visibility and alternating between a dewpoint depression of 0F and 1F. So with rounding, my hunch is that they're actually around 99% RH in reality. They had a low of 53F.

LCI is coming out of the fog now, but had a similar deal. Mostly 0F, but some 1F dewpoint depressions in the 5 minute obs...probably about 99% RH. They were also 1/8-1/4SM and had a low of 54F.

Awesome! I opened my package that has the 75 sensor in it and I didnít realize how small that sensor really was. Lol
Very small and very responsive. My setup really is like the raw data from an ASOS. I may move my sensor up to a full 2m (6.5ft) to pull it away from the sfc heating as much as possible without going over the 2m mark (40 CFM fan remember). Either that or I'll put a 5 minute averaging algorithm on the data. For now I'm just accepting the raw readings for what they are. If I put my hand briefly under the air intake of the shield I see a spike in temperature in my data.

Nice!
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline openvista

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Well... it happened. Looks like my good 31 just went bad on humidity.

My first sign was when I noticed this evening the FARS dewpoint exceeded the "bad" 31 in my passive shield. That was my "oh shite" moment.

I just measured a 10% humidity error with my Kestrel. Today has been quite brisk with well-mixed conditions, overcast, NW winds. The airport, which is about 15 miles inland (normally difficult to compare to except on days like this), is reporting a 50 degree dewpoint (I was showing 53.3 vs 49.6 on my Kestrel).

What preceded this? Fog and mist last night. Reached 94% humidity for the first time since July 1st.

Maybe it will snap back once we get a dry spell (tomorrow?). But I'm not holding my breath.

 :evil: :evil: :evil:
« Last Edit: August 21, 2018, 08:09:32 PM by openvista »
Davis Vantage Pro2 FARS | https://marquetteweather.com | EW7933

Online galfert

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Well... it happened. Looks like my good 31 just went bad on humidity.


So that was what? Like 2 and a half weeks old? This is the new 31 in the 7714 right?
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Tele-Pole flag pole is here (not installed yet)

 

anything