Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?

[CW2274]

Well, now that non-soon 2019 has left the building, I thought I'd state my final-ish opinion (see what the winter brings as well) on this latest 31 and it's performance to date. I would not hesitate for one second to buy this again. No idea if this 31 is a fluke, or Davis has finally figured out what was occurring with their mounting technique, but it's been fantastic. One other possible reason that I've found this 31 to be so good is that it has had the SF2 cap on it from day one, I've never done that before. It acts as a barrier to an extent and may very well help with over-saturation and what not, and it recovers perfectly fine. Me having a case fan may also help with the "process".
All of this is not scientific, just my relentless study. Thing is, as much as I've preached this sensor from day one, not one, single person that I'm aware of (and I've lobbied) has tried to see whether I'm full of it or it's truly legit.

Guess we'll never know...I'll be enjoying it regardless.

[Old Tele man]

Old Japanese proverb: "No FIXEE what ain't BROKEE."



P.S. -- I'm still using my 31's (yep, I've got more than one in service).

[CW2274]

Old Japanese proverb: "No FIXEE what ain't BROKEE."

Well, that's just it, everybody and their brother says it sucks...and there's been tons of data that backs that conclusion. All I've been saying is that perhaps the issue has been dealt with.

[WheatonRon]

Old Japanese proverb: "No FIXEE what ain't BROKEE."

Well, that's just it, everybody and their brother says it sucks...and there's been tons of data that backs that conclusion. All I've been saying is that perhaps the issue has been dealt with.

Possibly dealt with but based on prior experience unlikely. Davis has such a great tool if they would only pay attention to details and feedback from us enthusiasts. The SHT31 and spoon tipper just to name two. I can live with a horribly dated and ugly console but these two weaknesses are fundamental to the integrity of a pws.

[CW2274]

Old Japanese proverb: "No FIXEE what ain't BROKEE."

Well, that's just it, everybody and their brother says it sucks...and there's been tons of data that backs that conclusion. All I've been saying is that perhaps the issue has been dealt with.

Possibly dealt with but based on prior experience unlikely.

And frankly tired of saying this over and over, you'll never know til you try.

Damn people, it's not like I'm asking y'all to buy a $1000 piece of equipment that you can't return, it's $40....and you can return it. I'm sick and tired of being the only who's TRYING here. If it still sucks, oh well, send the GD thing back. Mine works fine.

[WheatonRon]

Old Japanese proverb: "No FIXEE what ain't BROKEE."

Well, that's just it, everybody and their brother says it sucks...and there's been tons of data that backs that conclusion. All I've been saying is that perhaps the issue has been dealt with.

Possibly dealt with but based on prior experience unlikely.

And frankly tired of saying this over and over, you'll never know til you try.

Damn people, it's not like I'm asking y'all to buy a $1000 piece of equipment that you can't return, it's $40....and you can return it. I'm sick and tired of being the only who's TRYING here. If it still sucks, oh well, send the GD thing back. Mine works fine.

I have tried three times with this sensor and failed each time. I really don’t like returning items. Adds too much complexity to a small business like Ryan and other honest business people run.

[CW2274]

Old Japanese proverb: "No FIXEE what ain't BROKEE."

Well, that's just it, everybody and their brother says it sucks...and there's been tons of data that backs that conclusion. All I've been saying is that perhaps the issue has been dealt with.

Possibly dealt with but based on prior experience unlikely.

And frankly tired of saying this over and over, you'll never know til you try.

Damn people, it's not like I'm asking y'all to buy a $1000 piece of equipment that you can't return, it's $40....and you can return it. I'm sick and tired of being the only who's TRYING here. If it still sucks, oh well, send the GD thing back. Mine works fine.

I have tried three times and failed. I really don’t like returning items too. Adds too much complexity to a small business like Ryan and other honest business people run.

Fine. Ryan has stated to me all his returns go back to Davis, that's his business. You'd think after countless returns to Davis, they'd start to get the picture....that's the whole point of returns here.

[ValentineWeather]

As I've said before I'm sensor poor 5-SHT31's and 10+ SHT 75's and in no need of another for years. The last one I purchased even properly packaged displayed the same high humidity bias as before.  I use the SHT75 during the spring, summer and the 31 during the fall, winter when dewpoints are well below the trouble point 60's +.   
I'm sure someone in one of the chronic high dewpoint regions year-round will eventually purchase and hopefully give you/us some feedback.

[CW2274]

dewpoints trouble point 60's +

No trouble for me...as in none...zip, zero, zilch.

[CW7491]

I wish my experience and enthusiasm matched those of CW2274. Unfortunately, they do not.

Despite good sense from Johnd and others, I couldn’t resist purchasing a Davis 6834 mostly because I assumed it was an SHT31 and because their spec sheet notes it is for indoor use only as the sensor is unshielded. https://www.davisinstruments.com/product_documents/weather/spec_sheets/6834%20Temp%20Hum%20Sheet.pdf

My hope was that the unshielded sensor would be mounted differently and therefore might produce better results (along the lines of the Acurite SHT31). Upon receipt, however, I found that it is literally the exact same outdoor 31 and filter with just a plastic casing for mounting. The date sticker on the sensor is June 2019. Without even having been brought outdoors, the sensor has a high humidity bias compared to my Belfort 566 and my SHT75 that has been outdoors for 6 mos.

No doubt these sensors do better in arid areas (which unfortunately doesn’t describe western Washington), but even straight out of the packaging, I see no improvement with a newly manufactured Davis 31, although I’m happy to see CW2274 getting improved results. For me, I’m done hoping for an improvement in these Davis sensors, unless they acknowledge a change or someone posts a demonstrable change in these sensors. Unfortunately, as many have noted, that is very unlikely.

Finally, for those tinkerers, I’ve mounted my SHT75 in a sintered metal temperature humidity probe casing I found on Amazon (from China, of course) and I’ve had good results. It’s an AM2305. https://www.ebay.com/i/382584872953?rt=nc&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20160908110712%26meid%3Db49d3475180242579b83524be24642eb%26pid%3D100677%26rk%3D11%26rkt%3D30%26sd%3D283587140916%26itm%3D382584872953%26pmt%3D0%26noa%3D1%26pg%3D2386202  I’ve noticed most high end temp/hum sensor manufacturers (Vaisala etc) use sintered filters. I’ve removed the included sensor and wires and inserted my soldered SHT75.

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[ValentineWeather]

Thanks for the update sorry to hear there was no difference. I still use a silk material for a filter and works well.

[Tensor]

BTW: How exactly close are the Dew Points between the HYT sensors and the official observations?

I'm still running the comparisons. So far HYT221 seems to rise slower to higher humidity levels than the official one. It has also maxed out to 99.99% at super humid day. Dew points are very close to each other, if it's windy and humidity is less than 90.

And for everybody who are interested, here's another guy's realtime comparison of Vaisala and SHT31: https://www.mrsoft.fi/current.htm
I bet his Vaisala sensors are of type HMP60 or HMP110 (the cheapest ones you can buy from Vaisala). If I had spare money, I would buy also one of those and compare SHT31, HYT221 and HMP60 in the exactly same conditions.

[jerryg]

Ok so i just ordered another 31 for testing from Ryan at S.I. now that we are getting into the high humidity season down here on the coast near the Gulf of Mexico. I sometimes get humidity readings above 95% for days at a time during the winter months. I think i am wasting my money but just have to try one more time to see if i can get a good long run of good readings. My accurite meter has been outside a lot over the last year and is still working just fine so i know the 31 can work real well over a long period of time. Will get it set up and running for the winter and will give updates as needed.

[ValentineWeather]

Ok so i just ordered another 31 for testing from Ryan at S.I. now that we are getting into the high humidity season down here on the coast near the Gulf of Mexico. I sometimes get humidity readings above 95% for days at a time during the winter months. I think i am wasting my money but just have to try one more time to see if i can get a good long run of good readings. My accurite meter has been outside a lot over the last year and is still working just fine so i know the 31 can work real well over a long period of time. Will get it set up and running for the winter and will give updates as needed.

Nice Jerry, now we will know for sure 
I like you seriously doubt there are any changes other than packaging. I think our conclusion was the molding process onto the board was the main problem. The Accurite doesn't use this process and even sensirion warns VOC's can harm the humidity sensor. 

[CW2274]

Ok so i just ordered another 31 for testing from Ryan at S.I. now that we are getting into the high humidity season down here on the coast near the Gulf of Mexico. I sometimes get humidity readings above 95% for days at a time during the winter months. I think i am wasting my money but just have to try one more time to see if i can get a good long run of good readings. My accurite meter has been outside a lot over the last year and is still working just fine so i know the 31 can work real well over a long period of time. Will get it set up and running for the winter and will give updates as needed.

Nice Jerry, now we will know for sure 

Granted, I don't live in the most humid of places, but I've spent the last two months with dew points consistently in the 60's. The monsoon doesn't always bring rain, but it always brings humidity and the 31 did fine. Just sayin'..........

[krojan]

Today I came across such a page comparing different sensors:

https://wiki.liutyi.info/display/ARDUINO/Test+0+v6+room+RH35+with+fan+unstable+board

Maybe it will be useful to someone.

[jgentry]

BTW: How exactly close are the Dew Points between the HYT sensors and the official observations?

I'm still running the comparisons. So far HYT221 seems to rise slower to higher humidity levels than the official one. It has also maxed out to 99.99% at super humid day. Dew points are very close to each other, if it's windy and humidity is less than 90.

And for everybody who are interested, here's another guy's realtime comparison of Vaisala and SHT31: https://www.mrsoft.fi/current.htm
I bet his Vaisala sensors are of type HMP60 or HMP110 (the cheapest ones you can buy from Vaisala). If I had spare money, I would buy also one of those and compare SHT31, HYT221 and HMP60 in the exactly same conditions.

Do you think the slowness of HYT’s humidity responsiveness is due to the siting of that sensor? I remember you saying that it wasn’t ideally sited.

[CW2274]

Please get them and let us know. It’s a sensor that I recommended Davis to consider switching too. Would love to see how the HYT would match up with a nearby ASOS or a Psychro-Dyne

I don't have a FARS, so HYT 221's humidity level may lag behind the truth at calm evenings. At days, the lag doesn't seem to be so large, because the days are rarely calm here.

I agree with this assessment, no fan. Sitting has nothing to do with responsiveness, only accuracy. 

[jerryg]

Ok got my new sensor in this afternoon and i removed the filter and wrapped it in a damp washcloth for a couple of hours to get it moistened up. It is now outside and under test and it is reading the same as my other two stations so now for the long haul testing.

[CW2274]

wrapped it in a damp washcloth for a couple of hours to get it moistened up.

Not saying it's wrong or right, but I didn't do that. The only thing I did different was use the SF2 cap from the get-go.

[WheatonRon]

wrapped it in a damp washcloth for a couple of hours to get it moistened up.

Not saying it's wrong or right, but I didn't do that. The only thing I did different was use the SF2 cap from the get-go.

I must have missed the post. What is a SF2 cap and where do I get one?

[CW2274]

https://www.mouser.com/ProductDetail/Sensirion/SF2?qs=wWC4CIiyLaNCAejbFUK5dw%3D%3D

[ValentineWeather]

It should be a good test looking at Jerry's dewpoint this morning. 
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[jerryg]

Short first report, the humidity with the two 75 sensors maxed at 97% and the new 31 maxed at 98% and went down to 97% after 30 minutes. The wind was calm and one of the 75 sensors is in a Barani standard passive shield while the other 75 as well as the 31 are in modified Davis 24 hour shields that run with fan on during the day and off at night. The mod makes the shield a passive shield at night and fan added during the day and has been giving good results. When the fans turned on the 31 humidity began to drop first with the 75 with fan on lagging behind by a few minutes and the Barani passive did not start to drop until wind started to blow at 2 to 3 mph. Will update later when humidity drops a lot more to see how the 31 does against the 75.

[jerryg]

Update, i just moved the 31 to my website so i can monitor it from anywhere. It is working just fine right now and now have to see if it keeps on going.