Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 72487 times)

0 Members and 1 Guest are viewing this topic.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5908
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
even in fog mist my station only got to 96%.
Well, I suppose you could try the "baking method" if you wanted.

Offline fkapp

  • Senior Contributor
  • ****
  • Posts: 224
Thanks. overall am happy as has been smooth operation. dialing in is the next chapter.
To be honest the baking the sensor process makes me nervous am going to damage the sensor.
If a mishap happens can always replace the sensor :).

What tips for baking do you have and I read a toaster oven is an option?

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5908
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Thanks. overall am happy as has been smooth operation. dialing in is the next chapter.
To be honest the baking the sensor process makes me nervous am going to damage the sensor.
If a mishap happens can always replace the sensor :).

What tips for baking do you have and I read a toaster oven is an option?
"Dialing in" humidity is almost always a two way street..rob Peter to pay Paul. You may fix one end, but trash the other. Then again, here I see the full range from 1% to 100%, so perhaps you can get it where you want it more so than I.

Read back in the thread for baking procedures, I've never done it.

Offline jerryg

  • Forecaster
  • *****
  • Posts: 865
  • weather is never boring
    • victoria texas weather
Well need to update my post too, the new 31 has been doing ok but like the other 31 it maxed out at 98% so i went ahead an baked it and now it hits a solid 99%. We have had a few nights of dense fog and it has been solid and shows no signs of any wet bias at all. I decided to bake the older 31 again because it was a little slower than the new one and it now follows the new one just fine plus with a dense fog and 99% showing it bumps 100% every so often so the baking did help it some. The old 31 is still trucking along with no problems seen.

Offline fkapp

  • Senior Contributor
  • ****
  • Posts: 224
Forgot to mention that I came across a used wireless weather monitor II that I setup for my son who is in elementary as his first weather station as a science project together.

The analog sensor in the WMII after good cleaning is working very well and on this same fog mist morning hit 100% for several hours.  Impressed that after all these years still working accurately.

Just wanted to mention that another WM II is still going strong

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5908
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
The analog sensor in the WMII after good cleaning is working very well and on this same fog mist morning hit 100% for several hours.  Impressed that after all these years still working accurately.
Yes, the old analog sensors seem to have little trouble pulling the 100% trigger unlike the current digital batch. No idea how they did/do in the other extreme. Being so old, there may be some drift to watch for if you care.


Offline jerryg

  • Forecaster
  • *****
  • Posts: 865
  • weather is never boring
    • victoria texas weather
Update the newest 31 is still working fine with no bias seen and works good from low humidity to the max of 99%.  =D>

Offline jgentry

  • Forecaster
  • *****
  • Posts: 521
On an interesting note....There is a guy on the WeatherFlow forum that received his WeatherFlow Tempest station yesterday and the SHT31 in the Tempest has performed really well so far.  The humidity sensor reached to 100% this morning.

Here is his station webpage. https://tempestwx.com/station/18140/ and https://smartweather.weatherflow.com/station/18140/grid

Here are the surrounding NWS/RAWS stations
 https://mesowest.utah.edu/cgi-bin/droman/trend_zip_mm.cgi?zipcode=33186&type=0&radius=25&noho=1&rawsflag=1&orderby=p&mode=
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline drew1021

  • Senior Contributor
  • ****
  • Posts: 197
Sorry to break in to the conversation but I was hoping someone could point me in the right direction to the instructions on how to bake the 31 as so many have successfully accomplished. Thanks.
VP2 with 24 hour FARS. WU: KNCLEWIS2. CWOP/APRS: DW4712, COCORAHS: NC-FR-7

Offline galfert

  • Global Moderator
  • Forecaster
  • *****
  • Posts: 6686
Sorry to break in to the conversation but I was hoping someone could point me in the right direction to the instructions on how to bake the 31 as so many have successfully accomplished. Thanks.

From Sensirion's datasheet...

Reconditioning Procedure
The following reconditioning
procedure may bring the sensor back to calibration state:
Baking: 100 Ė 105įC at < 5%RH for 10h
Re-Hydration: 20 Ė 30įC at ~ 75%RH for 12h
Ecowitt GW1000 | Meteobridge on Raspberry Pi
WU: KFLWINTE111  |  PWSweather: KFLWINTE111
CWOP: FW3708  |  AWEKAS: 14814
Windy: pws-f075acbe
Weather Underground Issue Tracking
Tele-Pole

Offline drew1021

  • Senior Contributor
  • ****
  • Posts: 197
So do you wrap the sensor with foil and place it on a baking sheet
VP2 with 24 hour FARS. WU: KNCLEWIS2. CWOP/APRS: DW4712, COCORAHS: NC-FR-7

Offline jerryg

  • Forecaster
  • *****
  • Posts: 865
  • weather is never boring
    • victoria texas weather
What i use and it works real well is a cheap table top toaster oven that i set with a calibrated thermometer  to 220 degrees and it cycles between 215 to 225. It has worked real well on several sensors that i just put in the oven without any wrapping. I place it towards the front door so it doesn't get too close to the element. I have not had any type of melting problem with the temperature being that low.

Offline drew1021

  • Senior Contributor
  • ****
  • Posts: 197
Great idea, not sure I want to buy a toaster oven just for this though.
VP2 with 24 hour FARS. WU: KNCLEWIS2. CWOP/APRS: DW4712, COCORAHS: NC-FR-7

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5908
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Great idea, not sure I want to buy a toaster oven just for this though.
Celebrate afterwards with some tater tots...

Offline Intheswamp

  • Early on one frosty morn'...
  • Forecaster
  • *****
  • Posts: 1482
  • Sure...I know enough to be dangerous, now.
    • Beeweather

Davis VP2, v3.12
Cumulus v1.9.4  Build 1079
Today's weather beats no weather at all!
www.beeweather.com
Nope, I still haven't replaced that humidity sensor... DONE!<grin>

Offline jgentry

  • Forecaster
  • *****
  • Posts: 521
Iíve now have some experience with two WeatherFlow Tempest weather stations. Not sure how they did it, but the SHT-31 in their station doesnít have any wet bias issues and it easily goes up to 100%. Keep in mind that this happens right out of the box and itís before WF does any further calibrations to it.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline CW7491

  • Contributor
  • ***
  • Posts: 106
I thought about starting a new topic, but thought the input keeps with the continuity of this original topic.

I recently compared the SHT85 with the SHT75 in my Davis VP2 as well as a Davis mounted SHT31. I was able to get the data from the SHT85 with an old USB test kit I had from Sensirion and their RS485 Sensor Viewer 2.91 software. The siting of the SHT85 was not desirable due to cable length restrictions, but the sensor comes with its own sensor-mounted filter and I placed it in the Davis 7714 radiation shield. If temperatures between the sensors were the same, I was able to compare humidity values directly. In times when they weren't, I used dewpoint.

Initially, the SHT85 data seemed promising, running 6-8 percentage points lower in humidity than the SHT75 (2-3įF lower in dewpoint). Even after a period of high humidity, where both sensors reached 98%, the SHT85 would read a lower humidity when the air dried out again. Unfortunately, after a longer period of high humidity, the high humidity bias presented itself in the SHT85 and pretty much matched the SHT75 exactly. After the test, I brought the high bias SHT85 and SHT75 inside to compare with the Davis-mounted SHT31 which I have baked previously and has been inside in low humidity. Both the SHT75 and SHT85 perform about the same or a little better even with the high humidity bias present.

Offline jgentry

  • Forecaster
  • *****
  • Posts: 521
I thought about starting a new topic, but thought the input keeps with the continuity of this original topic.

I recently compared the SHT85 with the SHT75 in my Davis VP2 as well as a Davis mounted SHT31. I was able to get the data from the SHT85 with an old USB test kit I had from Sensirion and their RS485 Sensor Viewer 2.91 software. The siting of the SHT85 was not desirable due to cable length restrictions, but the sensor comes with its own sensor-mounted filter and I placed it in the Davis 7714 radiation shield. If temperatures between the sensors were the same, I was able to compare humidity values directly. In times when they weren't, I used dewpoint.

Initially, the SHT85 data seemed promising, running 6-8 percentage points lower in humidity than the SHT75 (2-3įF lower in dewpoint). Even after a period of high humidity, where both sensors reached 98%, the SHT85 would read a lower humidity when the air dried out again. Unfortunately, after a longer period of high humidity, the high humidity bias presented itself in the SHT85 and pretty much matched the SHT75 exactly. After the test, I brought the high bias SHT85 and SHT75 inside to compare with the Davis-mounted SHT31 which I have baked previously and has been inside in low humidity. Both the SHT75 and SHT85 perform about the same or a little better even with the high humidity bias present.

Iím wondering if how Davis mounts their 31 on the PCB causes the 31 not to ďair outĒ fully; which causes the wet bias issues to be ďpermanent.Ē
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline CW7491

  • Contributor
  • ***
  • Posts: 106
Yeah, I was disappointed with the SHT85. There are definitely two issues: a Sensirion sensor characteristic at prolonged high humidity and Davisí application of the sensor which demonstrably worsens/makes permanent the sensorís high humidity bias.

Offline jerryg

  • Forecaster
  • *****
  • Posts: 865
  • weather is never boring
    • victoria texas weather
Just to add to the mix i have an old 31 that i had out for some time and it showed the bias of 3% high which is keeping with the specs of the sensor which is the sensor will read high after being in a high humidity setting of more than 80% for three days are more and will only return to the normal reading after being below the 80% for some time as it says the return will be very slow. I put the new 31 out and it has been very good with the low and high end readings with a lot of 100% readings in heavy fog. I put the 31 back out in a different shield and sure enough after a long period of drying out it read 1% lower than the new 31 and has been holding that for several weeks. We haven't got into a run of high humidity yet so won't know what happens until i get a good run of above 80% to set the stage for the error to show up. Now i think the baking works well because of the very low humidity in the oven and makes for a faster recovery time but just keeping it below 80% for sometime works the same just slower. This time of year i can get periods of above 80% for a week at a time so i will just have to wait for that to happen.

Offline jgentry

  • Forecaster
  • *****
  • Posts: 521
Just to add to the mix i have an old 31 that i had out for some time and it showed the bias of 3% high which is keeping with the specs of the sensor which is the sensor will read high after being in a high humidity setting of more than 80% for three days are more and will only return to the normal reading after being below the 80% for some time as it says the return will be very slow. I put the new 31 out and it has been very good with the low and high end readings with a lot of 100% readings in heavy fog. I put the 31 back out in a different shield and sure enough after a long period of drying out it read 1% lower than the new 31 and has been holding that for several weeks. We haven't got into a run of high humidity yet so won't know what happens until i get a good run of above 80% to set the stage for the error to show up. Now i think the baking works well because of the very low humidity in the oven and makes for a faster recovery time but just keeping it below 80% for sometime works the same just slower. This time of year i can get periods of above 80% for a week at a time so i will just have to wait for that to happen.

Iím curious if the 31 was mounted correctly, it would return back into calibration quicker than the Davisí setup?
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5908
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Just to add to the mix i have an old 31 that i had out for some time and it showed the bias of 3% high which is keeping with the specs of the sensor which is the sensor will read high after being in a high humidity setting of more than 80% for three days are more and will only return to the normal reading after being below the 80% for some time as it says the return will be very slow. I put the new 31 out and it has been very good with the low and high end readings with a lot of 100% readings in heavy fog. I put the 31 back out in a different shield and sure enough after a long period of drying out it read 1% lower than the new 31 and has been holding that for several weeks. We haven't got into a run of high humidity yet so won't know what happens until i get a good run of above 80% to set the stage for the error to show up. Now i think the baking works well because of the very low humidity in the oven and makes for a faster recovery time but just keeping it below 80% for sometime works the same just slower. This time of year i can get periods of above 80% for a week at a time so i will just have to wait for that to happen.

Iím curious if the 31 was mounted correctly, it would return back into calibration quicker than the Davisí setup?
If you recall, the Acurite device that utilized the 31 had no bias compared to the Davis mounted 31. I kinda thought we were done with this fiasco. Yes, I know, I'm in the desert, but my current 31 is 18 months old and I remain very happy with it. I still think a sealed SF2 cap is a difference maker in the big scheme of things.

Offline CW7491

  • Contributor
  • ***
  • Posts: 106
You certainly can be done with the fiasco if you wish, I just was providing input for anyone who is interested in the SHT85. For those of us in humid climates, the fiasco is real. The SHT85 is a Sensirion mounted SHT35 with a PTFE membrane right on the sensor. Unfortunately the 85 performs exactly like the SHT75 in a humid climate despite the hope it might do better. And yes, the one thing that hasnít changed is in my experience and climate, the SHT75 and 85 are superior to the Davis mounted 31.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5908
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
You certainly can be done with the fiasco if you wish, I just was providing input for anyone who is interested in the SHT85. For those of us in humid climates, the fiasco is real. The SHT85 is a Sensirion mounted SHT35 with a PTFE membrane right on the sensor. Unfortunately the 85 performs exactly like the SHT75 in a humid climate despite the hope it might do better. And yes, the one thing that hasnít changed is in my experience and climate, the SHT75 and 85 are superior to the Davis mounted 31.
I quoted and replied to 'jgentry'...not you.

Offline CW7491

  • Contributor
  • ***
  • Posts: 106
Understood. Itís an open forum and Iím replying to you.

 

anything