Author Topic: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?  (Read 1260 times)

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Offline weather34

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DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« on: February 20, 2019, 02:00:13 AM »
DAVIS VP2 (SHT31) humidity is it really a widespread issue ???

I have spent months watching and reading various SHT31 threads and the continuous non Davis owners jump on the band wagon so I was all always a bit skeptical but always followed with interests of those with the actual hardware and their various findings and admired their knowledge and tests and modifications .
So I awaited the day when I would wake up and see the dense FOG roll off the sea front on a calm day and this morning it did (see photo) . When I first installed my Davis VP2 the following day it was similar conditions and I swore blind i saw a figure of 99% but at the time I wasn't connected to any device for recording charts or displaying external it was just running on the console for display. So this morning I was able to log it .see screenshots below..
So what does this highlight ? is a production batch issue ? does the environment/location come into play ? is it really a flaw as what some non owners highlight ?

I don't dispute anyones realtime , real world findings, chamber tests its those I follow with interest ..so hope its of interest ...oh and the dvd is a bird reflector i get plagued by small birds sitting in between the spikes especially the young ones , birds hate reflective objective google is
your friend on the subject of bird reflectors but i got the idea from my father when I was a youth(1970s) he always hung tin foil nearby his vegetation to care of the birds..






« Last Edit: February 20, 2019, 02:32:52 AM by weather34 »

Offline weather34

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #1 on: February 20, 2019, 03:13:36 AM »
oh its now sitting at 100% and local Int Ataturk airport FWIW at aprox 10km  line of sight across the water peninsula..
only flaw I see is the actual dewpoint readout on the console is rounded up as it does not have capability of displaying decimal's for dewpoint  !!!



« Last Edit: February 20, 2019, 03:15:43 AM by weather34 »

Offline ValentineWeather

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #2 on: February 20, 2019, 10:44:53 AM »
DAVIS VP2 (SHT31) humidity is it really a widespread issue ???



Yes, the main issue isn't whether it will reach 100% some sensors will others won't.

The issue is high humidity bias which gives ridiculous high heat indices during the hot summer months. This bias isn't necessarily linear but most noticeable during these hot humid periods when dew points are already running high.
The other problem many in humid climates see is oversaturation where humidity will run high for days.
Randy

Offline weather34

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #3 on: February 20, 2019, 10:51:41 AM »
ok thanks come july august ill be able to confirm or not if it is the case , a period of being unbearably humid and horrendous dewpoint sometimes you dont need a device to tell you , just seeing the sweat on your arms without doing anything apart from walk 10 meters....anyway thought id clarify the reporting of 100% is not an issue for all seem to reference somewhere a lot of people were topping max at 97% and has i type the fog returns as the sun goes down ....many thanks for the info..brian

Offline galfert

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #4 on: February 20, 2019, 01:37:18 PM »
You don't need to be a Davis owner to see the evidence of the SHT31 issues. I've seen several Davis systems with both the humidity high bias and also not reaching 100% humidity. It throws off dew points and upsets some seeking perfect marks with CWOP reporting also. What I also notice is that some flat line at some point. Some flat line at 96%, some at 92%, and even some at 87%. Sometimes when they get really bad, probably after years of neglect, when they flat line they sometimes crash hard where the humidity indicates that it dropped to I don't know 30% or something really low when it clearly is still above 90% humidity. Then when they crash hard they wont recover until the humidity lowers and matches the flat line point and then they pick up and continue showing proper reduction in humidity. I've help several people identify this problem from neighbors to others that just put their station online. The issue is real. It seems to affect some stations sooner than others. But there seems to be a consensus that around 18 months it is time to replace the sensor. If you have a VP2 it isn't as big of a deal. Because you have the option to buy a $50 sensor. But if you have a Vue ISS then there is no over the counter replacement. Here in Florida we see 100% humidity year round, like just about every night almost. Some people have taken their sensors out and tried to recondition them by baking them (260 Deg C) for 10 hours and then re-hydrating submitting to 75% RH for 10 or 12 hours. That has had some success but not enough to warrant it and the better recommendation is to replace the sensor instead. It is also not uncommon for this to happen to stations that are within their warranty period. The good news there is they get a new sensor for free and hopefully that will last them 18 months more.
 
« Last Edit: February 20, 2019, 01:43:09 PM by galfert »
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Offline weather34

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #5 on: February 20, 2019, 02:20:21 PM »
I will have to wait until july/august and draw my own conclusion but thanks for insight ..and having just been woken by a rather strong earth tremor(5.1) nearby still trembling really hate the feeling .. now looking out the window visibility of about 10 meters and another 100% reading and this afternoon i noticed a good response change as it began to drop when the fog receded as the sun broke through ..


Offline LFWX

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #6 on: April 10, 2019, 08:30:55 PM »
What I also notice is that some flat line at some point. Some flat line at 96%, some at 92%, and even some at 87%. Sometimes when they get really bad, probably after years of neglect, when they flat line they sometimes crash hard where the humidity indicates that it dropped to I don't know 30% or something really low when it clearly is still above 90% humidity

Well, this all sounds very familiar. 87% maximum no matter how foggy it is. Then suddenly it "seemed" to start working correctly, only to end up being all over the place a few days later (single digit humidity when it's been raining all day). It even hit 1% a few times - no, I don't live in a desert.

I know what I'll be working on over Spring Break.
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Offline galfert

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #7 on: April 10, 2019, 08:40:18 PM »
What I also notice is that some flat line at some point. Some flat line at 96%, some at 92%, and even some at 87%. Sometimes when they get really bad, probably after years of neglect, when they flat line they sometimes crash hard where the humidity indicates that it dropped to I don't know 30% or something really low when it clearly is still above 90% humidity

Well, this all sounds very familiar. 87% maximum no matter how foggy it is. Then suddenly it "seemed" to start working correctly, only to end up being all over the place a few days later (single digit humidity when it's been raining all day). It even hit 1% a few times - no, I don't live in a desert.

I know what I'll be working on over Spring Break.

Yup, I just checked your CWOP. Sensor definitely needs to be replaced.
https://www.scaledinstruments.com/shop/davis-instruments/davis-7346-070-pro2-digital-temperature-humidity-sensor-sensiron-sht31/

Don't forget to check your manufacturing code to see if you need to adjust the temperature calibration after replacing.
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Offline CW2274

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Re: DAVIS VP2 (SHT31) humidity is it really a widespread issue ?
« Reply #8 on: April 10, 2019, 08:41:00 PM »
What I also notice is that some flat line at some point. Some flat line at 96%, some at 92%, and even some at 87%. Sometimes when they get really bad, probably after years of neglect, when they flat line they sometimes crash hard where the humidity indicates that it dropped to I don't know 30% or something really low when it clearly is still above 90% humidity

Well, this all sounds very familiar. 87% maximum no matter how foggy it is. Then suddenly it "seemed" to start working correctly, only to end up being all over the place a few days later (single digit humidity when it's been raining all day). It even hit 1% a few times - no, I don't live in a desert.

I know what I'll be working on over Spring Break.
That's just a bad sensor, doesn't matter what it is.