Author Topic: ASOS visit with VP2 in hand  (Read 5455 times)

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Offline ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #75 on: July 18, 2017, 04:14:46 PM »
So now I have a box of board mounted SHT31's coming.

I'll test them with the EK-H4. I have all this free time now and still can't get away from this stuff.  :lol:



Nice  =D>
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Offline kcidwx

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Re: ASOS visit with VP2 in hand
« Reply #76 on: July 24, 2017, 12:20:26 AM »
Here's what I use to test humidity sensors across the range.





« Last Edit: July 24, 2017, 12:59:04 AM by kcidwx »
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Offline dendrite

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Re: ASOS visit with VP2 in hand
« Reply #77 on: July 24, 2017, 11:39:04 AM »
Nice toy. If you ever get bored of them you can donate them here.  :-P

Offline Old Tele man

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Re: ASOS visit with VP2 in hand
« Reply #78 on: July 24, 2017, 01:44:09 PM »
So, you don't use the "salted-water vapor" in plastic bag/container method? Just straight water vapor?
« Last Edit: July 24, 2017, 01:46:21 PM by Old Tele man »
• SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB
• CWOP: DW6988 - 2 miles NNE of Cortaro, AZ
• WU - KAZTUCSO202, Countryside

Offline kcidwx

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Re: ASOS visit with VP2 in hand
« Reply #79 on: July 24, 2017, 03:38:55 PM »
So, you don't use the "salted-water vapor" in plastic bag/container method? Just straight water vapor?

Correct. The saturated salt solution/plastic bag method is not accurate. When using a salt solution it has to be contained to a very tiny area and the sensor has to be a couple millimeters above the solution to be accurate. For example if you are doing the 75% RH test, the humidity is only 75% within a few millimeters of the salt solution. That's why they make tiny calibrating chambers like this.

http://www.vaisala.com/en/products/humidity/Pages/HMK15.aspx
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Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #80 on: July 24, 2017, 06:13:00 PM »
Here's what I use to test humidity sensors across the range.
Wow, is that from the 70's? (certainly nothing wrong with that) How do you know that it's properly calibrated itself?

Offline kcidwx

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Re: ASOS visit with VP2 in hand
« Reply #81 on: July 24, 2017, 08:50:17 PM »
Once the heating or cooling bulbs go off, it's calibrated and you can read the sensor you are testing. It will maintain the humidity level until you turn off the unit. It's fairly old but there's no date on it. This one was retired from the weather office and once it was decommissioned I offered $20 for it. Deal was accepted.  :lol:
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Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #82 on: July 24, 2017, 09:33:40 PM »
I just ran the patent #, it was filed in 1959! Here's the link https://www.google.com/patents/US3171473

Offline ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #83 on: July 24, 2017, 09:39:36 PM »
That's almost as old as me ;)
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Offline kcidwx

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Re: ASOS visit with VP2 in hand
« Reply #84 on: July 24, 2017, 10:59:28 PM »
I looked it up via serial number with the government NSN and it was manufactured in 03-77. Probably says that on the metal tag but the numbers have faded to unreadable. Still works great. No parts available though. These were built like a tank. I always throw an NIST reference device in when testing just to make sure it's working right. My only concern is I believe it uses R12 refrigerant so I hope it doesn't leak out.
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Offline hwcorder

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Re: ASOS visit with VP2 in hand
« Reply #85 on: July 27, 2017, 02:43:44 PM »
Work at the CWO at Charlotte Douglas Int'l Airport. We have a VP2 located at the office and just from experience (no official comparison) the VP2 dewpoint runs an average of about 1-2F above the asos but there are times when the VP dew point is lower. Our office is located about 1.5 miles away from the ASOS sensor group so you have to take this with a grain of salt.
Even across an airport as large as CLT you can have localized microclimates. The only way you could truly know is to set the sensors side by side.
« Last Edit: July 27, 2017, 02:47:07 PM by hwcorder »

Offline drew1021

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Re: ASOS visit with VP2 in hand
« Reply #86 on: April 01, 2018, 07:24:56 AM »
What ever happened to the days of using a highly accurate mercury psychrometer to verify humidity? Certainly cheaper. I recently switched over to the sht31 and am still waiting for a foggy morning when I can do a comparison. Davis claims accuracy of +/-2% from 1-100% Sensiron is claiming +-3% for their analog version.
« Last Edit: April 01, 2018, 08:12:33 AM by drew1021 »
VP2 with 24 hour FARS. SHT31 sensor technology

Offline jgentry

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Re: ASOS visit with VP2 in hand
« Reply #87 on: July 08, 2018, 07:26:07 PM »
I should also state that I tested three SHT31's in the 100% RH environment at the same time and got mixed results. However, after looking at the specs, the maximal tolerance at 100% is 3.5%. So they would be considered in specification. The sensor in front in the photo below is the one in the photo I posted above. For that sensor I was testing repeatability. That is the sensors ability to indicate the same value when exposed to the same conditions.




The sensors maximum allowable error is 2.5% and that escalates above 90% RH.





While I was at it, I ran the daughters WMII sensor through the same test. It did get to 100% but it took 38 minutes.




That tells me that you’re lucky if you hit 100%. Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #88 on: July 08, 2018, 07:41:37 PM »


Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Compared to what? Seriously folks, what else is better that we can realistically use?

Offline Old Tele man

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Re: ASOS visit with VP2 in hand
« Reply #89 on: July 08, 2018, 07:56:51 PM »


Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Compared to what? Seriously folks, what else is better that we can realistically use?
After reading that UK paper, it seems by switching to capacitive-RH sensors, they traded ONE problem (dry bias) for TWO (albeit cheaper) problems (wet bias & variability).

Should we go 'back' to sling psychrometers maybe?
« Last Edit: July 08, 2018, 07:58:56 PM by Old Tele man »
• SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB
• CWOP: DW6988 - 2 miles NNE of Cortaro, AZ
• WU - KAZTUCSO202, Countryside

Offline ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #90 on: July 08, 2018, 08:09:13 PM »


Should we go 'back' to sling psychrometers maybe?

I broke too many... :lol:
Randy

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #91 on: July 08, 2018, 08:09:54 PM »


Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Compared to what? Seriously folks, what else is better that we can realistically use?
Should we go 'back' to sling psychrometers maybe?
Dunno about you, but uploading that data every five minutes 24/7 365 might.. just might get a little tiresome.... :mad:

Offline Old Tele man

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Re: ASOS visit with VP2 in hand
« Reply #92 on: July 08, 2018, 08:19:17 PM »


Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Compared to what? Seriously folks, what else is better that we can realistically use?
Should we go 'back' to sling psychrometers maybe?
Dunno about you, but uploading that data every five minutes 24/7 365 might.. just might get a little tiresome.... :mad:
Actually, I was thinking more about a dual-temp & wet-sock (wetbulb depression) unit; fitted into an AC-fan aspirated shield it should work OK, but getting clean/fresh distilled water to it might get interesting during either a dust storm or dust-devil.
« Last Edit: July 08, 2018, 08:26:32 PM by Old Tele man »
• SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB
• CWOP: DW6988 - 2 miles NNE of Cortaro, AZ
• WU - KAZTUCSO202, Countryside

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #93 on: July 08, 2018, 08:25:55 PM »


Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Compared to what? Seriously folks, what else is better that we can realistically use?
Should we go 'back' to sling psychrometers maybe?
Dunno about you, but uploading that data every five minutes 24/7 365 might.. just might get a little tiresome.... :mad:
Actually, I was thinking more about a dual-temp & wet-sock temperature unit; fitted into an AC-fan aspirated shield it should work OK, but getting clean/fresh distilled water to it might get interesting during either a dust storm or dust-devil.
Thanks, but I'll be sticking to my auto-loading, crappy 31. :oops:

Offline jgentry

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Re: ASOS visit with VP2 in hand
« Reply #94 on: July 08, 2018, 08:59:00 PM »


Overall, your test tells us that the SHT-31 isn’t reliable when it comes to humidity readings
Compared to what? Seriously folks, what else is better that we can realistically use?
Should we go 'back' to sling psychrometers maybe?
Dunno about you, but uploading that data every five minutes 24/7 365 might.. just might get a little tiresome.... :mad:
Actually, I was thinking more about a dual-temp & wet-sock temperature unit; fitted into an AC-fan aspirated shield it should work OK, but getting clean/fresh distilled water to it might get interesting during either a dust storm or dust-devil.
Thanks, but I'll be sticking to my auto-loading, crappy 31. :oops:

Remember, your climate is more ideal for the SHT-31
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline WheatonRon

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Re: ASOS visit with VP2 in hand
« Reply #95 on: July 08, 2018, 08:59:59 PM »
Slow day in weatherland to dig up this dated topic. Oh well, WU continues to suck and kill great radar apps they once had; Davis ignores the need for a VP-3; CWOP as a website is so dated it is embarrassing but no one at NOAA cares since Russ Chadwick retired, despite volunteers like me who have offered to help bring CWOP somewhat up to date by at least identifying the hundred or so deadlinks in those webpages; —we must discuss something. The new WiFiLogger recently developed by Wojtek is a plus and the SHT31 is still a great tool despite words to the contrary in this thread.

All this said, life will continue more or less as we know it today!
« Last Edit: July 08, 2018, 09:04:41 PM by WheatonRon »
Davis VP2 with 24 hour FARS, SHT31 (3 complete systems-2 for uploading to the internet the other system for test and play); CWOP--CW5020 and FW3075; WU--KILWHEAT17 and KILWHEAT36; WeatherCloud.net; CoCoRaHS--IL-DP-132; Rainwise 111

Offline Old Tele man

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Re: ASOS visit with VP2 in hand
« Reply #96 on: July 08, 2018, 09:05:57 PM »
Slow day in weatherland to dig up this dated topic. Oh well, WU continues to suck and kill great radar apps they once had; Davis ignores the need for a VP-3; CWOP as a website is so dated it is embarrassing but no one at NOAA cares since Russ Chadwick retired, despite volunteers like me who have offered to help bring CWOP somewhat up to date by at least identifying the hundred or so deadlinks in those webpages; —we must discuss something. The new WiFiLogger recently developed by Wojtek is a plus and the SHT31 is still a great tool despite words to the contrary in this thread.

All this said, life will continue more or less as we know it today!
ANALOGY: "...and the can continues to be kicked down the road."
• SYS: Davis VP2 Vue/WL-IP & Envoy8X/WL-USB
• CWOP: DW6988 - 2 miles NNE of Cortaro, AZ
• WU - KAZTUCSO202, Countryside

Offline ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #97 on: July 08, 2018, 11:51:58 PM »
the SHT31 is still a great tool despite words to the contrary in this thread.



Sounds like you got lucky. Just dropped another $100 for two more Sensirion sensors. Gets old adjusting for bad humidity readings all day for website accuracy easier to just replace every few months.
 
On the bright side at about $50 pop with shipping you can buy 16 or so for the price of 1 Vaisala. 



 
Randy

Offline WxLover16

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Re: ASOS visit with VP2 in hand
« Reply #98 on: July 09, 2018, 08:04:00 PM »
the SHT31 is still a great tool despite words to the contrary in this thread.



Sounds like you got lucky. Just dropped another $100 for two more Sensirion sensors. Gets old adjusting for bad humidity readings all day for website accuracy easier to just replace every few months.
 
On the bright side at about $50 pop with shipping you can buy 16 or so for the price of 1 Vaisala.

Why do you think you keep getting bad humidity readings?
Davis Wireless VP2 SHT31 24hr 24CFM FARS

Offline WheatonRon

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Re: ASOS visit with VP2 in hand
« Reply #99 on: July 09, 2018, 08:47:23 PM »
the SHT31 is still a great tool despite words to the contrary in this thread.



Sounds like you got lucky. Just dropped another $100 for two more Sensirion sensors. Gets old adjusting for bad humidity readings all day for website accuracy easier to just replace every few months.
 
On the bright side at about $50 pop with shipping you can buy 16 or so for the price of 1 Vaisala.

Why do you think you keep getting bad humidity readings?

Read this thread, starting with those posted about July 4, 2018 to the present:

https://www.wxforum.net/index.php?topic=34658.0

I was in the camp of liking the SHT31, but when carefully reviewing the data from my 3 VP2s,  I now have a different view. Apparently, these sensors “wear out” after 12 to 18 months or so, a fact I find troubling, if true.
« Last Edit: July 09, 2018, 08:49:50 PM by WheatonRon »
Davis VP2 with 24 hour FARS, SHT31 (3 complete systems-2 for uploading to the internet the other system for test and play); CWOP--CW5020 and FW3075; WU--KILWHEAT17 and KILWHEAT36; WeatherCloud.net; CoCoRaHS--IL-DP-132; Rainwise 111

 

anything