Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 40971 times)

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Offline jgentry

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Here is Earth Networks (formerly WeatherBug) spec sheet for their stations. Will note that their DPs matches up well with ASOS stations
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Offline jgentry

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After 4 days with 2 new sensors, my conclusion they aren't much better than the old still running high on DP at those critical levels when its important to be most accurate (high heat index).

So basically I have 2 new sensors both now reach 98%.. Whoopie!  I'm beginning to think these sensors are just off. They surely don't come close to meeting the claimed specs when it counts.

I guess a key question is the temp at which Sensirion tests the sensors' humidity spectrum. My guess would be 25C (77F) since I see mention of it along with 63% in the notes on their datasheet. If they aren't testing beyond that, then, indeed, there could be discrepancies elsewhere.

I guess we should’ve paid attention to the “maximum accuracy” on Sensirion’s spec sheet. Lol
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline Aardvark

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perhaps bringing in the station to test it in a controlled environment to determine the difference between the sensor and the standard.

Davis has been moving the location of that sensor.   Initially it was fastened to the bottom of one of the radiation plates, but they moved it to the top of the next plate up because water was  collecting just enough that it saturated the sensor. Now if you have a FARS, as I do, the unit is mounted on its side in the chamber. 

How much of a difference if the sensor is removed from the chamber and tested vs.  one of the current 3 prime locations in the chamber.
Davis VP2 Plus; 24h  FARS; Extra Temp Humid sensor (2); Extra Temp Station (2); Soil Moisture/Temp  https://www.weatherlink.com/embeddablePage/show/1c484adbfa914d1aa10a58ad53ccd563/summary;Weatherlink IP;USB; MAC Mojave; Webcam;

Offline ValentineWeather

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After 4 days with 2 new sensors, my conclusion they aren't much better than the old still running high on DP at those critical levels when its important to be most accurate (high heat index).

So basically I have 2 new sensors both now reach 98%.. Whoopie!  I'm beginning to think these sensors are just off. They surely don't come close to meeting the claimed specs when it counts.

I guess a key question is the temp at which Sensirion tests the sensors' humidity spectrum. My guess would be 25C (77F) since I see mention of it along with 63% in the notes on their datasheet. If they aren't testing beyond that, then, indeed, there could be discrepancies elsewhere.

I guess we should’ve paid attention to the “maximum accuracy” on Sensirion’s spec sheet. Lol

No kidding.. :sad:
Randy

Offline openvista

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They surely don't come close to meeting the claimed specs when it counts.

Just looking again at Davis' NIST traceable doc (link posted above) and it says they verify humidity to be within +/- 3% between 33% and 90% with the checkpoints being 33%, 80% and 90%. Please notice they skip testing the most common middle ranges.

Once again, the question arises: at what temperature(s) are they testing humidity? They don't say. You could assume they use the temperature checkpoints, but I don't like assuming.

So even if you pay to have the humidity certified, we still don't know if the device is accurate in the most problematic middle ranges.
« Last Edit: July 17, 2018, 06:44:17 PM by openvista »
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Offline openvista

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perhaps bringing in the station to test it in a controlled environment to determine the difference between the sensor and the standard.

How much of a difference if the sensor is removed from the chamber and tested vs.  one of the current 3 prime locations in the chamber.

This is why I bark at you for parachuting into the thread and not bothering to do the least bit of reading. If you had read page 14, for instance, you'd see that Ron had run extensive tests in his humidity chamber and reproduced the wet bias. Then again, Ron's results from his laboratory-grade instrument are just another of 420 "opinions" right?
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Offline Aardvark

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perhaps bringing in the station to test it in a controlled environment to determine the difference between the sensor and the standard.

How much of a difference if the sensor is removed from the chamber and tested vs.  one of the current 3 prime locations in the chamber.

This is why I bark at you for parachuting into the thread and not bothering to do the least bit of reading. If you had read page 14, for instance, you'd see that Ron had run extensive tests in his humidity chamber and reproduced the wet bias. Then again, Ron's results from his laboratory-grade instrument are just another of 420 "opinions" right?
Would you please leave me alone.  Why do you seem to think you are in charge here.   I have reported you to the moderators and  definitely they need to step in and quell your hatred toward me and anything I ask .  Just leave me alone. Stop harassing me.
Davis VP2 Plus; 24h  FARS; Extra Temp Humid sensor (2); Extra Temp Station (2); Soil Moisture/Temp  https://www.weatherlink.com/embeddablePage/show/1c484adbfa914d1aa10a58ad53ccd563/summary;Weatherlink IP;USB; MAC Mojave; Webcam;

Offline openvista

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Look, lots of people have given freely of their time, expertise and money to try to understand and solve a problem that's not their fault. Some of us have thousands invested in a company that, apparently, thinks it can bait and switch us with impunity.

Given the circumstances, it's not a straight line to the answer. We don't have the same testing facilities as the manufacturer. We have to do our best with what we have. The situation, unfortunately, is still evolving on a trial and error basis.

So I find it awfully insulting when someone drops by every couple hundred posts and ask us if we're done yet. That's why I gave you the response I did. Had it been a lighter thread, then I'm sure I would have responded differently or not at all. My apologies.

Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline hwcorder

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Look, lots of people have given freely of their time, expertise and money to try to understand and solve a problem that's not their fault. Some of us have thousands invested in a company that, apparently, thinks it can bait and switch us with impunity.

Given the circumstances, it's not a straight line to the answer. We don't have the same testing facilities as the manufacturer. We have to do our best with what we have. The situation, unfortunately, is still evolving on a trial and error basis.

Yep can't even calculate the time and money I've put in and continue to put in to try to figure it out.  Seems like until Davis ditches this Digital Sbus protocol for the I2C they have us by the you know what. Unless someone here wants to try to build there own ISS transmitter that has a I2C microcontroller I don't see a whole lot of other options other than switching these sensors out every year or so.

Would love to try these sensors out as they look promising but alas, wrong protocol.
https://www.ist-ag.com/en-us/products/hyt-221-calibrated-and-temperature-compensated

Offline CW2274

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I'll duplicate this, forum member "ct" where are you....?

Offline jgentry

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Look, lots of people have given freely of their time, expertise and money to try to understand and solve a problem that's not their fault. Some of us have thousands invested in a company that, apparently, thinks it can bait and switch us with impunity.

Given the circumstances, it's not a straight line to the answer. We don't have the same testing facilities as the manufacturer. We have to do our best with what we have. The situation, unfortunately, is still evolving on a trial and error basis.

Yep can't even calculate the time and money I've put in and continue to put in to try to figure it out.  Seems like until Davis ditches this Digital Sbus protocol for the I2C they have us by the you know what. Unless someone here wants to try to build there own ISS transmitter that has a I2C microcontroller I don't see a whole lot of other options other than switching these sensors out every year or so.

Would love to try these sensors out as they look promising but alas, wrong protocol.
https://www.ist-ag.com/en-us/products/hyt-221-calibrated-and-temperature-compensated

Looks like this one might work best in high humidity environments.

Here is the data sheet- https://www.ist-ag.com/sites/default/files/DHHYT221_E.pdf

Application notes- https://www.ist-ag.com/sites/default/files/AHHYTM_E.pdf
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline hwcorder

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Look, lots of people have given freely of their time, expertise and money to try to understand and solve a problem that's not their fault. Some of us have thousands invested in a company that, apparently, thinks it can bait and switch us with impunity.

Given the circumstances, it's not a straight line to the answer. We don't have the same testing facilities as the manufacturer. We have to do our best with what we have. The situation, unfortunately, is still evolving on a trial and error basis.

Yep can't even calculate the time and money I've put in and continue to put in to try to figure it out.  Seems like until Davis ditches this Digital Sbus protocol for the I2C they have us by the you know what. Unless someone here wants to try to build there own ISS transmitter that has a I2C microcontroller I don't see a whole lot of other options other than switching these sensors out every year or so.

Would love to try these sensors out as they look promising but alas, wrong protocol.
https://www.ist-ag.com/en-us/products/hyt-221-calibrated-and-temperature-compensated

Looks like this one might work best in high humidity environments.

Here is the data sheet- https://www.ist-ag.com/sites/default/files/DHHYT221_E.pdf

Application notes- https://www.ist-ag.com/sites/default/files/AHHYTM_E.pdf

Actually mentions one of the typical applications for the HYT221 for measuring humidity in saunas lol! Wonder how it recovers afterwards though?

Offline jgentry

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Look, lots of people have given freely of their time, expertise and money to try to understand and solve a problem that's not their fault. Some of us have thousands invested in a company that, apparently, thinks it can bait and switch us with impunity.

Given the circumstances, it's not a straight line to the answer. We don't have the same testing facilities as the manufacturer. We have to do our best with what we have. The situation, unfortunately, is still evolving on a trial and error basis.

Yep can't even calculate the time and money I've put in and continue to put in to try to figure it out.  Seems like until Davis ditches this Digital Sbus protocol for the I2C they have us by the you know what. Unless someone here wants to try to build there own ISS transmitter that has a I2C microcontroller I don't see a whole lot of other options other than switching these sensors out every year or so.

Would love to try these sensors out as they look promising but alas, wrong protocol.
https://www.ist-ag.com/en-us/products/hyt-221-calibrated-and-temperature-compensated

Looks like this one might work best in high humidity environments.

Here is the data sheet- https://www.ist-ag.com/sites/default/files/DHHYT221_E.pdf

Application notes- https://www.ist-ag.com/sites/default/files/AHHYTM_E.pdf

Actually mentions one of the typical applications for the HYT221 for measuring humidity in saunas lol! Wonder how it recovers afterwards though?

Maybe kcidwx will get one of those sensors and put it in his humidity chamber and see how it does.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline ValentineWeather

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Looks like max is 90% humidity if I read the data sheet correctly.
Randy

Offline jgentry

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It goes up to 100%. I think the accuracy is +/-3% 90-100
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline jgentry

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Interesting to note that the RainWise MK III uses the Sensirion SHT 15 as their temperature/humidity sensor.
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Offline jerryg

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Ok new info on the nist calibration check on the 31, that previous info was old stuff and Ryan got an email from Davis and the new info is a 3 point check of +/- 1% at 33% and 80% and +/-2% at 90%. Looks a little better but i think they should have included one around 97%. When you look at a lot of the sensors most of the really good readings are confined to 30 to 90%, not many give much in the way of a good shot of accuracy about 90%.

Offline CW2274

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FWIW the published literature shows most capacitive sensors go WET above about 90ºF DP...so, asking for "exactness" might be futile...for now.
And when is the last time you saw a dew point AOA 90F? :shock: I know I sure as hell wouldn't live there.
« Last Edit: July 18, 2018, 06:43:52 PM by CW2274 »

Offline JudinNorman

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Ok new info on the nist calibration check on the 31, that previous info was old stuff and Ryan got an email from Davis and the new info is a 3 point check of +/- 1% at 33% and 80% and +/-2% at 90%. Looks a little better but i think they should have included one around 97%. When you look at a lot of the sensors most of the really good readings are confined to 30 to 90%, not many give much in the way of a good shot of accuracy about 90%.

Is a correction chart included like I have with my old max and min thermometers ?

Offline CW2274

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FWIW the published literature shows most capacitive sensors go WET above about 90ºF DP...so, asking for "exactness" might be futile...for now.
And when is the last time you saw a dew point AOB 90F? :shock: I know I sure as hell wouldn't live there.
Ooops, (typo) that should've been 90%RH:oops:
Ahhh, that sounds better! I guess I should feel fortunate that I have a sensor that'll hit 1% as well as 99.

Offline ValentineWeather

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FWIW the published literature shows most capacitive sensors go WET above about 90ºF DP...so, asking for "exactness" might be futile...for now.
And when is the last time you saw a dew point AOB 90F? :shock: I know I sure as hell wouldn't live there.

You mean Houston  :shock:
Randy

Offline CW2274

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FWIW the published literature shows most capacitive sensors go WET above about 90ºF DP...so, asking for "exactness" might be futile...for now.
And when is the last time you saw a dew point AOB 90F? :shock: I know I sure as hell wouldn't live there.

You mean Houston  :shock:
No doubt! I have no idea how those people deal with that stuff all-summer-long.

Offline ValentineWeather

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Got 2 new SHT31's in handled by a different company lets see if they do any better. I just happen to have passive shield I may try. Getting data could be an issue however they do record high and lows however.
 
Good point was brought up why rainwise sensors seem better using the SHT15 on mid to high dp temps in 60-80 range.

Something was brought to my attention by someone not on this thread the molding process Davis uses to mount sensor could be contamination source dooming sensor from getgo. Maybe that's why the reckless handling.

The sensor looks embedded in rubber or plastic which would be against all handling procedures. 

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Randy

Offline CW2274

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Got 2 new SHT31's in handled by a different company lets see if they do any better. I just happen to have passive shield I may try. Getting data could be an issue however they do record high and lows however.
 
Good point was brought up why rainwise sensors seem better using the SHT15 on mid to high dp temps in 60-80 range.

Something was brought to my attention by someone not on this thread the molding process Davis uses to mount sensor could be contamination source dooming sensor from getgo. Maybe that's why the reckless handling.

The sensor looks embedded in rubber or plastic which would be against all handling procedures. 

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Randy if I were you, I'd just look for some shade, or make your own.

Offline ValentineWeather

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Got 2 new SHT31's in handled by a different company lets see if they do any better. I just happen to have passive shield I may try. Getting data could be an issue however they do record high and lows however.
 
Good point was brought up why rainwise sensors seem better using the SHT15 on mid to high dp temps in 60-80 range.

Something was brought to my attention by someone not on this thread the molding process Davis uses to mount sensor could be contamination source dooming sensor from getgo. Maybe that's why the reckless handling.

The sensor looks embedded in rubber or plastic which would be against all handling procedures. 

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Randy if I were you, I'd just look for some shade, or make your own.

Good idea easier to see for sure.
Randy

 

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