Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 31635 times)

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Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1275 on: September 28, 2018, 05:15:19 PM »
Heads up for anyone wanting to change over to SHT75 and not great at soldering.
Digikey is about out of the Senserion cables 10' long with the 4 prong sht75 pin adapter.  These need the RJ plug changed or splice in existing Davis RJ connector.
 
Jerry just did a couple up for another forum member and reported the 2-outside wires need swapped on RJ to work.

Reason I'm posting these cables are no longer being made and soon the SHT75 is also out of production.
Only place I've found the cables is Digikey with 6 left today. 3 weeks ago 70+ in stock so someone or ones, snagging them up. 

https://www.digikey.com/product-detail/en/sensirion-ag/3M-CABLES-FOR-EK-H4/1649-1055-ND/5982944

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

  

Offline jgentry

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For those with the 75: Does the 75 goes back to calibration after prolong periods of RH being over 80% or does the sensor began to have a permanent wet bias?
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline jerryg

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I had a very wet period where the humidity was over 80 for several days and my sensor was showing about 2 higher, so i replaced it and after a day i put it back out this pm and it is tracking with the others, the 2 seems to be gone. All of the sensors have that caution warning about this quirk. At least it looks like it will clear up.

Offline jgentry

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I had a very wet period where the humidity was over 80 for several days and my sensor was showing about 2 higher, so i replaced it and after a day i put it back out this pm and it is tracking with the others, the 2 seems to be gone. All of the sensors have that caution warning about this quirk. At least it looks like it will clear up.

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

  

Offline jgentry

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I had a very wet period where the humidity was over 80 for several days and my sensor was showing about 2 higher, so i replaced it and after a day i put it back out this pm and it is tracking with the others, the 2 seems to be gone. All of the sensors have that caution warning about this quirk. At least it looks like it will clear up.

Are you still using the 75 for your website?
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline jerryg

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Yes

Offline jgentry

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Got the 75 installed in one of my field stations yesterday evening. Recorded a peak RH of 98% this morning which matches up with most Davis stations that has the 31 inside of a FARS. Iíve noticed the DP being the same to 1į lower at times compared to the stations with the 31 sensors. Other times, itís been 2-3į lower than the 31s. The surrounding airports still around 1-3į cooler with most of the time only being 1-2į cooler. Only one time today that the DP on the 75 was cooler than the surrounding airports (1-3į).

You can view the surrounding NWS/RAWS stations here:

https://mesowest.utah.edu/cgi-bin/droman/trend_zip_mm.cgi?zipcode=35171&radius=55&noho=1&rawsflag=1&orderby=p&hour1=21&day1=04&month1=10&year1=2018&type=0&mode=

You can view my field station with the 75 here:

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=E6358&unit=0&time=&hours=24&hour1=21&day1=04&month1=10&year1=2018&radius=25&past=0&order=1

Here is a nearby station that has the 31 inside of a FARS

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=F0139&unit=0&time=&hours=24&hour1=21&day1=04&month1=10&year1=2018&radius=25&past=0&order=1
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline jgentry

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I noticed today that the nearby VP2 station that has the 31 inside of FARS recorded the same peak DP of 75į. The lowest DP was recorded early this morning and was only 1į difference.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Online CW2274

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Do you guys think it's possible that Davis has addressed and corrected the problem and haven't said anything (I truly don't think they'll ever admit a problem exists), or happenstance that 31's seem playing well more so with others?

Offline jgentry

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Do you guys think it's possible that Davis has addressed and corrected the problem and haven't said anything (I truly don't think they'll ever admit a problem exists), or happenstance that 31's seem playing well more so with others?

Donít know...All I know is that the nearby station with the 31 is three years old. Sensor hasnít been replaced.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Online CW2274

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Do you guys think it's possible that Davis has addressed and corrected the problem and haven't said anything (I truly don't think they'll ever admit a problem exists), or happenstance that 31's seem playing well more so with others?
Donít know...All I know is that the nearby station with the 31 is three years old. Sensor hasnít been replaced.
Not positive, but I think the 31 wasn't even available then. I installed my first one late 3/16 and I believe that was pretty much hot off the press.

Offline jgentry

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Do you guys think it's possible that Davis has addressed and corrected the problem and haven't said anything (I truly don't think they'll ever admit a problem exists), or happenstance that 31's seem playing well more so with others?
Donít know...All I know is that the nearby station with the 31 is three years old. Sensor hasnít been replaced.
Not positive, but I think the 31 wasn't even available then. I installed my first one late 3/16 and I believe that was pretty much hot off the press.

Iím mistaken then. Itís been 2 years and not three.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline WxLover16

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Do you guys think it's possible that Davis has addressed and corrected the problem and haven't said anything (I truly don't think they'll ever admit a problem exists), or happenstance that 31's seem playing well more so with others?
Donít know...All I know is that the nearby station with the 31 is three years old. Sensor hasnít been replaced.
Not positive, but I think the 31 wasn't even available then. I installed my first one late 3/16 and I believe that was pretty much hot off the press.

I believe I read on here somewhere that they started being shipped on some VP2's in December 2015. I could be wrong though.
Davis Wireless VP2 SHT31 24hr 24CFM FARS

Online CW2274

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Do you guys think it's possible that Davis has addressed and corrected the problem and haven't said anything (I truly don't think they'll ever admit a problem exists), or happenstance that 31's seem playing well more so with others?
Donít know...All I know is that the nearby station with the 31 is three years old. Sensor hasnít been replaced.
Not positive, but I think the 31 wasn't even available then. I installed my first one late 3/16 and I believe that was pretty much hot off the press.

I believe I read on here somewhere that they started being shipped on some VP2's in December 2015. I could be wrong though.
No sir. 31's weren't factory installed until last year. That doesn't mean they weren't available at that point for the retro fit on older ISS's like mine.

Offline dendrite

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I got a new ISS and 31 from Ryan a few weeks ago and I've been liking it so far. I had been using an old late 2006 ISS that came with an analog T/H when I bought it. After switching to digital sensors I had noticed I'd get strange spikes in RH a couple of times a day...i.e. I'd have an hour of something like 83-86% RH but I'd get 1 ob in there with 95% that would really stand out. That's gone now with the new transmitter.

The past few days I've been hitting 99% RH at night and the dewpoint has seemed on par during the day. I'm running it with the filter off and the fan at 9V.

Offline Old Tele man

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I got a new ISS and 31 from Ryan a few weeks ago and I've been liking it so far. I had been using an old late 2006 ISS that came with an analog T/H when I bought it. After switching to digital sensors I had noticed I'd get strange spikes in RH a couple of times a day...i.e. I'd have an hour of something like 83-86% RH but I'd get 1 ob in there with 95% that would really stand out. That's gone now with the new transmitter.

The past few days I've been hitting 99% RH at night and the dewpoint has seemed on par during the day. I'm running it with the filter off and the fan at 9V.
9VDC? Obviously, that's not a stock Davis FARS fan; what brand is it?
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Offline dendrite

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I got a new ISS and 31 from Ryan a few weeks ago and I've been liking it so far. I had been using an old late 2006 ISS that came with an analog T/H when I bought it. After switching to digital sensors I had noticed I'd get strange spikes in RH a couple of times a day...i.e. I'd have an hour of something like 83-86% RH but I'd get 1 ob in there with 95% that would really stand out. That's gone now with the new transmitter.

The past few days I've been hitting 99% RH at night and the dewpoint has seemed on par during the day. I'm running it with the filter off and the fan at 9V.
9VDC? Obviously, that's not a stock Davis FARS fan; what brand is it?
I'll have to find a link later. It's one of those 12V circular Xerox drum fans. I connect it to a variable AC adapter and run it at 9V because  it doesn't like to startup at 12V even though it's rated for it. I got tired of forgetting it's off when the power comes back on after an outage. At 9V, no issues.

Offline jgentry

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So far with the 75, I like it pretty good. During the day, the DP is either the same or a few degrees lower than the nearby 31s. Sometimes the DP is the same or +/-1į than the nearby airports. Other times, itís around a 2-3į difference with the 75 being wetter. For rest of yíall that have the 75, have yíall noticed the same thing? I will say that some weeds and other vegetation growing some underneath the station but nowhere high enough to be close the shield/sensor.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline CW7491

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This maybe should be in a new thread, but I recently found the preliminary data sheet on the new SHT85 ...

https://www.mouser.com/catalog/specsheets/Sensirion_10022018_HT_DS_SHT85_V0.9_D1.pdf

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This maybe should be in a new thread, but I recently found the preliminary data sheet on the new SHT85 ...

https://www.mouser.com/catalog/specsheets/Sensirion_10022018_HT_DS_SHT85_V0.9_D1.pdf
\:D/ However.... The Big But....Is the protocol compatible with our ISS's???

Offline galfert

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This maybe should be in a new thread, but I recently found the preliminary data sheet on the new SHT85 ...

https://www.mouser.com/catalog/specsheets/Sensirion_10022018_HT_DS_SHT85_V0.9_D1.pdf
\:D/ However.... The Big But....Is the protocol compatible with our ISS's???

I searched the whole document. I only see references to I2C protocol. So doesn't look good. No mention of LSS. I suppose there could always be a separate document for the LSS version.

I liked that the SHT85 has a built-in heater! That is new I think.
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Offline ValentineWeather

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If you look at the data sheet on SHT75 its says IC not IC2 so this is same problem other newer sensors have so probably won't work. I'm no expert however on what will work with Davis.
From what I have pieced together the Davis version of SHT31 was special production order because they don't advertise the Davis version at all on Sensirion website.
Davis uses a protocol that is backward compatible and proprietary.
The 75 looks like the only way to avoid the wet bias.
Randy

Offline graculus

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I liked that the SHT85 has a built-in heater! That is new I think.

The SHT1x and SHT3x series have all had heaters.

Most unlikely IMHO that they will offer this assembly (selected SHT3x on a stick?) in the older interface :-(

Offline rdsman

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Here is my take on this:

The SHT85 is pin for pin compatible with the SHT75 (electrically) and could be simply plugged in without any rewiring .  Although the SHT85 appears to be I2C only, a simple firmware upgrade for the ISS would be required.  As far as I know, this could only be done by Davis.

See:

https://www.mouser.com/catalog/additional/Sensirion_HT_AN_SHT85_Transitioning_SHT7x_to_SHT85_V0.9_D1.pdf



Ray

Offline ValentineWeather

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Here is my take on this:

The SHT85 is pin for pin compatible with the SHT75 (electrically) and could be simply plugged in without any rewiring .  Although the SHT85 appears to be I2C only, a simple firmware upgrade for the ISS would be required.  As far as I know, this could only be done by Davis.

See:

https://www.mouser.com/catalog/additional/Sensirion_HT_AN_SHT85_Transitioning_SHT7x_to_SHT85_V0.9_D1.pdf

Would be nice, either Davis or others figure out how. Specs on the X85 look really good.
Randy

 

anything