Author Topic: SHT31  (Read 9919 times)

0 Members and 1 Guest are viewing this topic.

Offline JudinNorman

  • Senior Member
  • **
  • Posts: 65
SHT31
« on: May 23, 2017, 12:32:51 PM »
Any weather station geeks care to share some thoughts on the SHT31 sensor Davis uses no in the VP2?  I'm wondering if it's worth the cost to upgrade if my current older sensor is working just fine.
Jud

Offline openvista

  • Forecaster
  • *****
  • Posts: 481
    • marquetteweather.com
Re: SHT31
« Reply #1 on: May 23, 2017, 01:32:00 PM »
If you have fan aspiration (FARS), expect to see the temperature change quite a bit more than you're accustomed to now. I was shocked at how responsive it is. Not saying that's a bad thing, but it makes comparisons with neighboring stations harder because almost inevitably their readings will lag your station even if comparisons are made in real time.

Beware that despite the tight stated accuracy specifications (+/- 0.38F from freezing upward), these are not NIST certified or pre-calibrated sensors. So their baseline may be off. In my case, I had to adjust mine -0.4F after averaging many comparison readings with a very accurate, certified check gauge. Every one of those check readings, whether taken on a breezy, cloudy, thermally-stable night or inside in my garage, showed the SHT31 to be biased warm up to 0.5F (the median was actually 0.45 but I'm conservative and put in a -0.4 offset).  Even after adjusting, continued checks have shown that a consistent warm bias appears to remain (somewhere on the order of 0.2F), although not enough to warrant further adjustment so far.

I'm not suggesting all SHT31s run warm, just advising you not to take the manufacturer's word for it. If you aren't overly concerned with fine accuracy, this may be a moot issue.
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline JudinNorman

  • Senior Member
  • **
  • Posts: 65
Re: SHT31
« Reply #2 on: May 23, 2017, 01:55:19 PM »
Thanks ya all for the comments.

In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?

Offline openvista

  • Forecaster
  • *****
  • Posts: 481
    • marquetteweather.com
Re: SHT31
« Reply #3 on: May 23, 2017, 02:38:38 PM »
In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?

Good question! I inquired as to the specs of my local COOP station and the NWS blew me off even though I addressed an employee who doubles as the CoCoRaHS coordinator for this region (and who had set me up a couple years back). We've had a couple positive email exchanges in the past. Maybe your local office will be more responsive.

Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be). Or perhaps it's better to take it on a case-by-case basis depending on the resources and conscientiousness of the local WFO. It could also come down to the difference between what the NWS is supposed to be doing versus what they are actually doing (or not doing). So even if the specs for their sensors are similar or better, who knows how accurate they are at any given moment.

The COOP records here are, to put it politely, a bit of a mess. Record keeping is inconsistent. One month last year, half the entries were missing! The sensor suite is sited within 20ft of a 25ft brick building wall. This is also where official precip, including snow, is measured. The nearby building shadows precip coming from several directions. Do I believe they calibrate this station? Not really. Could that be why they failed to respond to a simple question (asked very politely)? Perhaps.

Like I said, your mileage may vary.
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: SHT31
« Reply #4 on: May 23, 2017, 03:55:37 PM »
The original VP2 came with the SHT11. Some of the later VP2's were being shipped with SHT15's but within a year they changed over to the 31's. The SHT11's aren't very accurate especially below freezing at 0C-32F they are already +/- 1.1C (2°F) off and it gets much worse as temps drop. It also suffers on high end but not as bad.
 
The SHT15's are better but if you live in cold country the 31 is only way to go.
Randy

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: SHT31
« Reply #5 on: May 23, 2017, 04:08:28 PM »
openvista if you upgraded to the SHT31 sensor using the older transmitter build before Jan 2016 it needs the -.9 offset.
I've never found the SHT31 to run warm is why I'm saying this. I've crosschecked with NIST certified at 32F and found them very accurate needing no adjustment other than the -(.9) if using older transmitter. 

Correction Jan 2016 is the cut off date.
« Last Edit: May 23, 2017, 04:12:54 PM by ValentineWeather »
Randy

Offline johnd

  • Forecaster
  • *****
  • Posts: 4827
    • www.weatherstations.co.uk
Re: SHT31
« Reply #6 on: May 23, 2017, 04:16:57 PM »
Correction Jan 2016 is the cut off date.

Strictly speaking, you need to look for AS revision. There were some (a few) ISS units built post 1/1/2016 that don't have SHT31, but these would be recognisable as eg AR revision. So yes any SIM board pre-AS revision needs the offset.
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline openvista

  • Forecaster
  • *****
  • Posts: 481
    • marquetteweather.com
Re: SHT31
« Reply #7 on: May 23, 2017, 04:19:25 PM »
openvista if you upgraded to the SHT31 sensor using the older transmitter build before Jan 2017 it needs the -.9 offset.
I've never found the SHT31 to run warm is why I'm saying this. I've crosschecked with NIST certified at 32F and found them very accurate needing no adjustment other than the -(.9) if using older transmitter.

Yes, I should have clarified that. I started with a -0.9F offset as instructed by Davis and currently have it set to -1.3F (subtracting another 0.4F) based on my calibration checks. It could be that I drew a sensor that was anomalous, but if I did, then perhaps someone else could too. I will continue checking it in different conditions to be sure that the offset is correct (controlling for the necessary variables like radiation, hysteresis, FARS, siting, margin of error, etc).
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline spweather

  • Contributor
  • ***
  • Posts: 130
    • Sand Point Weather
Re: SHT31
« Reply #8 on: May 23, 2017, 04:29:49 PM »
Where is the best (least expensive) place to get this sensor?

Dennis
Regards,
Dennis

- Davis Wireless Vantage Pro2 Plus w/24hr FARS
- Davis (Ultra)Sonic Anemometer
- Boltek/MicroLDN TOA Lightening Detection
- Porcupine Labs LR4/Fluke 414D Laser Rangefinder snow depth measuring sensor


Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: SHT31
« Reply #9 on: May 23, 2017, 04:31:48 PM »
Yes! I have a problem Houston. I have triple redundancy setup with 3-sht31's aspirated shields and they are all very close. Even humidity is matching but does vary slightly more between sensors.
I trust the accuracy and like I said have cross checked with expired but once certified NIST certificate thermometers.   

This was our frost the other morning so took a snapshot. One last frost tonight I see just issued.
Randy

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: SHT31
« Reply #10 on: May 23, 2017, 04:33:14 PM »
Where is the best (least expensive) place to get this sensor?

Dennis

I use Scaled Instruments out of Florida most of the time for Davis Inst.
Randy

Offline WxLover16

  • Forecaster
  • *****
  • Posts: 479
Re: SHT31
« Reply #11 on: May 23, 2017, 05:16:49 PM »
Any weather station geeks care to share some thoughts on the SHT31 sensor Davis uses no in the VP2?  I'm wondering if it's worth the cost to upgrade if my current older sensor is working just fine.
Jud

I would say if you're a die-hard temperature-accuracy fanatic like I am, then the cost of the upgrade is worth it. The sensor is much improved from the 11. Faster response time and tighter specs. Can't go wrong, IMO. I'm just happy that my VP2 purchased in February last year already came with the 31. Also, if you take the filter off, the response time is INSANE! Many times I would get .2-.4 ups and downs with each update, it was crazy. However, that can dirty up the sensor so I put the filter back on.
Davis Wireless VP2 SHT31 24hr 24CFM FARS

Offline CW2274

  • Forecaster
  • *****
  • Posts: 6731
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: SHT31
« Reply #12 on: May 23, 2017, 05:43:38 PM »
In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be).
In the U.S., ASOS/AWOS are used for official measurements for a given particular area. Since practically all are located on an airport, regular maintenance/calibration is performed for safety of the flying public, ASOS's by the FAA, AWOS's by the NWS. (I'm sure there's exceptions). Whether RAWS for example are used in lieu if the others aren't physically near by, I do not know, but the ones in my area have been down before and fixed within a day or so.

Offline openvista

  • Forecaster
  • *****
  • Posts: 481
    • marquetteweather.com
Re: SHT31
« Reply #13 on: May 23, 2017, 07:04:11 PM »
In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be).
In the U.S., ASOS/AWOS are used for official measurements for a given particular area. Since practically all are located on an airport, regular maintenance/calibration is performed for safety of the flying public, ASOS's by the FAA, AWOS's by the NWS. (I'm sure there's exceptions). Whether RAWS for example are used in lieu if the others aren't physically near by, I do not know, but the ones in my area have been down before and fixed within a day or so.

Yes, there are exceptions. Of the 6 towns with records available on the website of my local Weather Forecast Office (WFO), only 1 of the stations is at an airport. 4 of them are at water treatment plants and 1 of them is a RAWS (remote automated weather station).

My town's COOP is run entirely by volunteers who are solely responsible for maintaining the continuity of 140+ years of records. I've previously described just how well that's going  :roll:. This should give you an idea of where it falls in the list of priorities overall. Like I said, your mileage may vary.
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline CW2274

  • Forecaster
  • *****
  • Posts: 6731
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: SHT31
« Reply #14 on: May 23, 2017, 07:20:01 PM »
In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be).
In the U.S., ASOS/AWOS are used for official measurements for a given particular area. Since practically all are located on an airport, regular maintenance/calibration is performed for safety of the flying public, ASOS's by the FAA, AWOS's by the NWS. (I'm sure there's exceptions). Whether RAWS for example are used in lieu if the others aren't physically near by, I do not know, but the ones in my area have been down before and fixed within a day or so.

My town's COOP is run entirely by volunteers who are solely responsible for maintaining the continuity of 140+ years of records. I've previously described just how well that's going  :roll:. This should give you an idea of where it falls in the list of priorities overall. Like I said, your mileage may vary.
Sad to see that "official" record keeping can be mitigated to the back burner. But, like you said, priorities.  :-|

Offline JudinNorman

  • Senior Member
  • **
  • Posts: 65
Re: SHT31
« Reply #15 on: May 24, 2017, 01:17:45 PM »
Thanks to all those who replied.  I'm going to be getting a new SHT31.
Jud


Offline Bashy

  • brecklandweather.com/meteo
  • Forecaster
  • *****
  • Posts: 1465
  • brecklandweather.com/index.php
    • Breckland Weather
Re: SHT31
« Reply #16 on: May 25, 2017, 02:00:41 AM »
Correction Jan 2016 is the cut off date.

Strictly speaking, you need to look for AS revision. There were some (a few) ISS units built post 1/1/2016 that don't have SHT31, but these would be recognisable as eg AR revision. So yes any SIM board pre-AS revision needs the offset.

Hi John, I got my setup from you in Feb '17, what temp will mine have in it please?
Kind regards
Bashy

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: SHT31
« Reply #17 on: May 25, 2017, 09:58:06 AM »
For transmitter firmware anything built Jan 2016 or later I've found through orders with Scaled Instruments had the latest SHT31 firmware. The code doesn't have to be AS or later despite what Davis says as long as it was manufactured in Jan 2016. You can open transmitter and look at first 4 numbers after the 2 letters.

Example code of AP160101201 (Jan 2016)
Randy

Offline Bashy

  • brecklandweather.com/meteo
  • Forecaster
  • *****
  • Posts: 1465
  • brecklandweather.com/index.php
    • Breckland Weather
Re: SHT31
« Reply #18 on: May 25, 2017, 09:59:57 AM »
Not that easy for me, mine is up on the mass :/
Kind regards
Bashy

Offline Bashy

  • brecklandweather.com/meteo
  • Forecaster
  • *****
  • Posts: 1465
  • brecklandweather.com/index.php
    • Breckland Weather
Re: SHT31
« Reply #19 on: May 25, 2017, 10:38:43 AM »
There's that Damn hind sight.....
Kind regards
Bashy

Offline JudinNorman

  • Senior Member
  • **
  • Posts: 65
Re: SHT31
« Reply #20 on: June 04, 2017, 08:26:35 PM »
A few days of the SHT31 being in service it's 0.2 to 0.4 F higher than my Davis Temperature station sensor for high and low temperatures while my old temp/hum sensor was 0.2 to 0.4 F colder than the Temperature station sensor.  It's a little disappointing my VP2 mean temperatures now will be around 0.4 to 0.8 F higher than the past 10 years just as a result of a simple sensor switch.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 6731
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: SHT31
« Reply #21 on: June 04, 2017, 08:53:55 PM »
it's 0.2 to 0.4 F higher than my Davis Temperature station sensor for high and low temperatures while my old temp/hum sensor was 0.2 to 0.4 F colder than the Temperature station sensor. 
Two things: Firstly, what's your "Davis Temperature station sensor" :?:  :???:
Secondly, how do you know it's not "wrong" and your 31 isn't "right"?

Offline CW2274

  • Forecaster
  • *****
  • Posts: 6731
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: SHT31
« Reply #22 on: June 04, 2017, 09:00:36 PM »
And just for further clarification, you stated in another thread that you did put in the minus 0.9F offset, right?

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 6364
    • Valentine Nebraska's Real-Time Weather
Re: SHT31
« Reply #23 on: June 04, 2017, 09:37:43 PM »
If the Davis had an older SHT11 remember they aren't as accurate and very likely was off, especially if several years old they can drift.
If comparing to a nearby professional station remember they most likely have ideal setup so wouldn't surprise me if you weren't reading higher in your back yard.
I would bet the SHT31 is accurate, and the older sensor has the problem.
Randy

Offline JudinNorman

  • Senior Member
  • **
  • Posts: 65
Re: SHT31
« Reply #24 on: June 04, 2017, 10:53:29 PM »
Davis Temperature station sensor is the sensor that is part of the Davis Temperature Station, just measures temperature,  no humidity.
Not sure which is right,  just disappointing after 10 years of data the new data will not be close.  It screws up the freeze data,  old sensor read 32.0 which would go down as a freeze but the new sensor would read 32.8 for example and would be considered a freeze.  My first and last freeze days will be off.
Jud

it's 0.2 to 0.4 F higher than my Davis Temperature station sensor for high and low temperatures while my old temp/hum sensor was 0.2 to 0.4 F colder than the Temperature station sensor. 
Two things: Firstly, what's your "Davis Temperature station sensor" :?:  :???:
Secondly, how do you know it's not "wrong" and your 31 isn't "right"?

 

anything