Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 70935 times)

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Offline CW2274

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Granted, only been a day, and it's dry, but the new 31 is nailing the dew point. Very pleased!

Offline dendrite

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Yeah, if you can work it out, I donít think the SF2 inside the stock filter will cost you much in response time with the fan.
What I'm trying to help alleviate is the wild temp swings that I see during max insolation as the heat eddies across the desert floor. With a 60CFM fan, those are sucked up like nobody's business. I have a 40CFM backup, but am not inclined to swap them at this time. When the stock filter starts to "dirty up", maybe I'll be more satisfied. Yep, dirtier may be better...well at least for me.
Have you compared the graphs between your station and KTUS? If youíre not aware, you can get the raw 1 minute historical ASOS readings from here.

ftp://ftp.ncdc.noaa.gov/pub/data/asos-onemin/

Choose the annual folder that begins with 6406...those have the temp/dew data in them. Theyíre large files so you have a lot of scrolling to go through to find the station youíre looking for.

Offline CW2274

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Yeah, if you can work it out, I donít think the SF2 inside the stock filter will cost you much in response time with the fan.
What I'm trying to help alleviate is the wild temp swings that I see during max insolation as the heat eddies across the desert floor. With a 60CFM fan, those are sucked up like nobody's business. I have a 40CFM backup, but am not inclined to swap them at this time. When the stock filter starts to "dirty up", maybe I'll be more satisfied. Yep, dirtier may be better...well at least for me.
Have you compared the graphs between your station and KTUS? If youíre not aware, you can get the raw 1 minute historical ASOS readings from here.
Yes I have, and I'm aware. Thank you.

Offline Intheswamp

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I hereby proclaim myself as "Procrastinator In Chief".  On April 24, 2016 I bought a Sensiron SHT31 from Ryan Wilhour and this afternoon I installed it!  :D  Not that I would take my own sweet time or anything.  It's nice to not be so dry around here...it had got down to 1% humidity and dewpoint down in the minus-twenties...really hazardous climate around here!!!  :lol: :lol:

Anyhow, it's "kind of" a dangerous procedure.  Here is a (semi) before and after picture...
IMG_0928a (Custom) by Ed Welch, on Flickr

Installed and ready to be remounted (a little cleanup job, too)...
IMG_0931a (Custom) by Ed Welch, on Flickr

My gardening buddy might stop telling me I live in Death Valley now!!!!

It's interesting, but my anemometer stopped working and I had to do a little trouble-shooting.  What I found was something had bit(?) the anemometer cable.  I cut that section out and spliced the pieces back together and all is well with the anemometer, too!  But, fixing that got me on a roll so in between rains today I got the sensor replaced, too!  [tup]  Lazy that I am....  :grin: :grin:
IMG_2126a (Custom) by Ed Welch, on Flickr
« Last Edit: March 26, 2021, 07:39:52 PM by Intheswamp »

Davis VP2, v3.12
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Nope, I still haven't replaced that humidity sensor... DONE!<grin>

Offline CW2274

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Jeez dude, 'bout time. 1% in Alabama? :-P That said, did you apply the -0.9F temp offset?

Offline Intheswamp

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<chuckle> Well, I knew I'd get around to it sooner.............................................................or later!  :lol:

Umm, besides taking my own sweet time I've skipped a few classes along the way.  The, uh, -0.9F temp offset? :-s

Davis VP2, v3.12
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Today's weather beats no weather at all!
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Nope, I still haven't replaced that humidity sensor... DONE!<grin>

Offline CW2274

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Your VP2 came with an SHT11, you replaced it with a 31, same as me and many others here. Since the protocol is different with the PCB, you'll need to subtract 0.9F from your console to correct for that fact.

Offline Intheswamp

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Thanks!  I'll get'er done!!!!!!!!!!! 

Now to go scrub the moss out of the rain bucket....  :roll:  I will say that the new(er) bucket with the bird spikes have made a BIG difference in debris in the bucket...I mean, basically ZERO debris!   =D&gt;

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

Offline Intheswamp

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It took me a couple of tries but I got the -0.9 offset keyed in.

I was interested in seeing changes in the humidity reading.  We had off-and-on rains yesterday so the humidity sensor was maxing out at around 95% after getting things put back together.  This morning was heavy fog with a saturated ground, the reading peaked at 98%.  Now it is finally dropping a bit...down to 92% at the moment.  I don't have to have perfection (ya think? :lol:) but it's good to have it back in a believable ballpark!  [tup]

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 Intheswamp

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I think I've got a new station!  :lol:

How long do most people get out of the SHT-31?  It looks like the original SHT-11 gave me around three years of service here in humid south Alabama.  Can I expect the SHT-31 give about the same service?

Davis VP2, v3.12
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Today's weather beats no weather at all!
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Nope, I still haven't replaced that humidity sensor... DONE!<grin>

Offline CW2274

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Don't know whether you've followed this very thread or not, but it's basically about how the Davis derived SHT31 can develop a wet bias after being subjected to a lot of high humidity. Since your sensor is literally the first batch released, this is something you may want to watch for. Whether Davis has addressed this issue or not is debatable, but it seems that it may have been. I'm in a very dry climate, so I'm not the best at judging this.

Offline Intheswamp

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Yes, I followed along with some of it...lots of it over my head but I did get the drift of water-logged sensors.  I wonder whether the finer screen on the cover might help some...and that's probably been discussed in the thread.  I'm gonna go with it lasting at least as long as the OE one.  I was needing to order a VP2 solar cover from Scaled Instruments and was going to order a backup sensor while I was at it.  But, I think I'll skip the sensor and see what happens.  No quicker than I got then one installed it can sit on the shelf in Florida as well as in Alabama.  :grin:  The solar cover is showing it's age, though.  Part of the locking clip broke a couple or three years ago and the screen protector is all fogged and cracking up...but it keeps working and it stays dry inside.  I may wait a little longer on it, too.  Glad to have the station back at 100%...I just need to get a weather-cam up again.

Davis VP2, v3.12
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Today's weather beats no weather at all!
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Nope, I still haven't replaced that humidity sensor... DONE!<grin>

Offline CW2274

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I know others probably think I'm full of it, but I swear by the SF2 cap. Is it an end-all-be-all solution, don't know, but I'll never go without it again.

Offline Intheswamp

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I'll see how it goes with the new cap, afterall...it's been 1% humidity around here for quiet a while...anything higher is improvement!! :lol:

I did save the old sensor and cap...something maybe to tinker with later...  [tup]

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

Offline CW2274

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I'll see how it goes with the new cap
Understood, however, the stock filter will do nothing to alleviate any potential bias, as it's merely still just that...the stock filter. The SF2 isn't and performs a much more protective roll.

Offline Intheswamp

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It looks like it requires modification to the cap?

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 CW2274

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This was reply #1636 I made a couple of weeks ago. You may want to read further after that.

"I wasn't thrilled about the glue option so I trimmed the four feet down to be flush with the base and used very thin stainless steel wire to wrap around the cap and cinch it down with pliers twisting from the back side. The wire doesn't come in contact with the membrane but arches over. With the "gooey" substance that surrounds the sensor it allows the cap to seat firmly in what I believe is a true seal."

Offline Intheswamp

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Ok, I get it.  I may go that route.  Thanks.

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>

 

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