Author Topic: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD  (Read 8586 times)

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Offline ValentineWeather

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Never thought I would become an advocate of a passive shield over FARS but yesterday I started testing the passive 7714 vs 24 hr. FARS and just the first day under clear sky and light winds the 7714 ran .5 to 1 lower than the FARS all day never having  afternoon spike like so many passive shields I've tested before did. I modified my shield with interior floor and roof painted flat black.

This is an inexpensive shield is why I'm excited and no moving parts.
 
The WMO did a study 2008-2009 using reference instruments. The passive 7714 actually got the highest 5 star rating and was cooler than reference and beat out the Davis FARS under light winds sunny conditions.

PDF of full study:  https://www.wmo.int/pages/prog/www/IMOP/publications/IOM-106_Ghardaia/IOM-106_Report.pdf

SDAVIS are the 2 passive 7714  and VDAVIS are the two FARS units tested.  0 is reference, you can see both performed well but most impressive the 7714 did better which confirms what I saw yesterday.

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These are the test summaries of both shields. Low wind the FARS did well but warmer than reference when wind came up and got a 3 star rating. The passive performed well all areas and got a 5 star rating.

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« Last Edit: August 04, 2018, 03:37:57 AM by ValentineWeather »
Randy

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #1 on: July 27, 2018, 09:18:27 AM »
Thanks for posting that! VERY applicable testing & analyses to people (like me) living in desert locations.

However, I would change this statement from the (8 plate) Davis 07714 booklet: "The radiation shield allows the temperature sensor to accurately measure air temperature without the effects of direct radiation from sunlight."

to this: "The radiation shield allows the temperature sensor to accurately measure air temperature without by mitigating the effects of direct radiation from sunlight."

« Last Edit: July 27, 2018, 09:34:59 AM by Old Tele man »
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Offline jgentry

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #2 on: July 27, 2018, 09:27:33 AM »
Interesting. But would there still be some lag time with that passive shield?
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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #3 on: July 27, 2018, 09:33:05 AM »
Interesting. But would there still be some lag time with that passive shield?
Smaller material volume means less HEAT buildup (and retension) as well as less material surface area acting like car radiator heating the incoming air. The more material the quicker the sun heat is captured and thus quicker to transfer more heat (larger radiator) into the incoming air; less material is opposite effect.
« Last Edit: July 27, 2018, 09:42:55 AM by Old Tele man »
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Offline dendrite

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #4 on: July 27, 2018, 09:38:30 AM »
I had the 7714 back in my WMII days. Then I got the Davis cabled FARS when that was a shiny and new product. The results were night and day for me. Way more response and cooler temps with the FARS. I'm glad you're happy with it, but I won't be going passive any time soon.

Do you have a pic showing them all setup together?

Online openvista

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #5 on: July 27, 2018, 10:14:19 AM »
OK, I just snagged the last 7714 in stock from Ryan. Gonna run this as my passive shield backup. I'll put a wet 31 sensor in there and see how temps perform. I will be SHOCKED if this thing can run neck and neck with my FARS with the AC fan inside long term.
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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #6 on: July 27, 2018, 10:17:03 AM »
Smaller material volume means less HEAT buildup (and retension) as well as less material surface area acting like car radiator heating the incoming air. The more material the quicker the sun heat is captured and thus quicker to transfer more heat (larger radiator) into the incoming air; less material is opposite effect.

If anything the 7714 with its 3 extra plates that are 1" longer than the stock Davis shield would present more thermal mass. It would seem the "magic" lies elsewhere... but where?

EDIT: I get now that you're comparing it to the FARS shield, but I still can't figure out how it outperforms the default passive shield (7710).
« Last Edit: July 27, 2018, 10:22:42 AM by openvista »
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Offline ValentineWeather

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #7 on: July 27, 2018, 10:19:14 AM »
Just finished switch over on remote station.  The study does show it's a great shield and my 1 day of testing seemed to confirm with no afternoon heat spike that has always made me stay away from passive shields. 

For now I'll just update this thread with a few daily graphs with no bias. I love accuracy so no bias, I'm as curious as the next and always thought fars was the way to go.

One thing I noticed in the study the Davis FARS was tagged as having a cool bias over reference shield in certain conditions and warm bias in others while the passive was same 97-99% of time. Anyone wondering how fast reaction time on temperature changes it scored well in testing.

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Randy

Offline ValentineWeather

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #8 on: July 27, 2018, 10:26:30 AM »
OK, I just snagged the last 7714 in stock from Ryan. Gonna run this as my passive shield backup. I'll put a wet 31 sensor in there and see how temps perform. I will be SHOCKED if this thing can run neck and neck with my FARS with the AC fan inside long term.

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Randy

Offline dendrite

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #9 on: July 27, 2018, 10:46:19 AM »
Heh. You have some wide open fields there. Maybe it would work for you with that much ventilation. No such luck at my place with all of the trees surrounding my yard. I'm lucky to get a 10mph gust on a fair weather summer day.

Offline kcidwx

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #10 on: July 27, 2018, 10:49:31 AM »
My daughters WMII temperature/humidity sensor has been in the 7714 for about 20 months. My Nimbus temperature probe is in a RM Young FARS a few feet away. I lab test both sensors every 12 months to check calibration. Looking at both of our 1-minute data over the last 20 months, her WMII under sunny/calm wind conditions has never been any higher than 1.8F above my temperature sensor. She's been as low as 1.9F below my temperature sensor at night.

In looking over the data, I've seen instances where she's been 3F to 4F above me. However, this was always right after a frontal passage where the temperature dropped significantly and that exposed some lag in her readings. Once the temperature stabilized, it was within 1F of me again. I actually found one instance where we dropped 15F in 10 minutes and she was 7F above me for a brief period of time.

I would never trade a FARS for a passive shield when it comes to temperature. However, if for whatever reason you want a passive shield, then the 7714 is the way to go. I've not tested one that works any better than the 7714.
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Offline dendrite

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #11 on: July 27, 2018, 10:51:54 AM »
The thing with the higher RH with the passive at night...

I generally noticed cooler temps with mins via radiational cooling with the passive since the shield and sensor experience some heat loss. Without forced air coming through, maybe it reaches condensation a little easier on the sensor.

The FARS is going to keep forcing air through there which increases the evaporation rate on the sensor/PCB and inhibits condensation trying to form.

It'd be interesting if you had a 75 in the passive shield. You'd probably gain any response time that you lost with the 31 + FARS combo.
« Last Edit: July 27, 2018, 10:54:13 AM by dendrite »

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #12 on: July 27, 2018, 11:11:06 AM »
I can see how passive would work out well in an open field (like the one pictured above) or in a well-ventilated back yard. However, we get so many low wind days/nights here in town, especially during the summer, that it might be tough for any passive shield to compete with my FARS.
« Last Edit: July 27, 2018, 11:17:06 AM by openvista »
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Offline ValentineWeather

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #13 on: July 27, 2018, 11:13:14 AM »
I think the only way to properly test is having matching thermometers. These SHT31's are all the same within .1F  but
if anyone wants to follow this Davis station with 7714 pictured above and airport ASOS I'll add links with 5 minute updates.


links with 5 minute updates about 2 miles distance.

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=E7498
https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=KVTN&unit=0&timetype=LOCAL/

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Randy

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #14 on: July 27, 2018, 11:24:19 AM »
Randy, do you visit Dr Steve Dimse's findU weather site? There, you can overlay selected local sites (yes, more than one) over your plots. For example, here's my DW6988 (blue) overlaid with local Marana airport KVAQ (purple):

https://weather.gladstonefamily.net/qchart/D6988?date=20180727&addnl=KAVQ&Add+to+charts=Add+to+charts&.cgifields=addnl

« Last Edit: July 27, 2018, 12:26:29 PM by Old Tele man »
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Offline dendrite

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #15 on: July 27, 2018, 11:25:40 AM »
Of course your local ASOS, that you're comparing to, is pumping the air through the sensor chamber too so the FARS really shouldn't be considered the root of the problem. It still goes back to the Davis sensor. If you're getting readings you like with the passive shield though then I guess the workaround works for you with your setup. It would still be nice to get the readings to jive with the FARS installed.

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #16 on: July 27, 2018, 11:33:34 AM »
Of course your local ASOS, that you're comparing to, is pumping the air through the sensor chamber too so the FARS really shouldn't be considered the root of the problem. It still goes back to the Davis sensor. If you're getting readings you like with the passive shield though then I guess the workaround works for you with your setup. It would still be nice to get the readings to jive with the FARS installed.

If the "problem" you're referring to is humidity measurement, the airport does not aspirate their humidity sensor. It's only minimally shielded from the elements, not contained within a standard radiation shield.

EDIT: I got that info from Ron (kcidwx) in the other thread about psychrometers and SHT31 humidity problems. However, in looking at the Wikipedia page for AWOS (https://en.wikipedia.org/wiki/Automated_airport_weather_station#Temperature_and_dew_point), it appears the modern systems use a radiation shield, just not, perhaps, aspirated.

Randy can correct me if I'm wrong, but I think he's just trying to establish temperature accuracy before tearing down his existing aspirated shields and replacing them with the 7714.
« Last Edit: July 27, 2018, 11:53:25 AM by openvista »
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Offline dendrite

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #17 on: July 27, 2018, 11:50:49 AM »
Of course your local ASOS, that you're comparing to, is pumping the air through the sensor chamber too so the FARS really shouldn't be considered the root of the problem. It still goes back to the Davis sensor. If you're getting readings you like with the passive shield though then I guess the workaround works for you with your setup. It would still be nice to get the readings to jive with the FARS installed.

If the "problem" you're referring to is humidity measurement, the airport does not aspirate their humidity sensor. It's only minimally shielded from the elements, not contained within a standard radiation shield.

Randy can correct me if I'm wrong, but I think he's just trying to establish temperature accuracy before tearing down his existing aspirated shields and replacing them with the 7714.

EDIT: I should probably clarify that it's the dew point sensor that is minimally shielded and humidity is derived from that.
True. Of course the Vaisala sensor is artificially heated to completely prevent condensation from forming on it. Then they have their algorithms to produce a fairly accurate Td. The whole topic has my brain spinning in circles and my migraine doesn't help.

Offline hwcorder

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #18 on: July 27, 2018, 01:32:26 PM »
Has anyone else tested one of these?

https://www.baranidesign.com/meteoshield-professional/

I've had mine in for about three days and happy with the results. Stats from MADIS have held about the same compared to ASOS station close to me and the last two days have been mostly sunny and fairly light wind. The shield is expensive for a passive and definitely more than the 7714. It's supposedly designed to protect the sensor from contamination in the way airflow is directed inside the chamber.
Edit: Forgot to add you will have to do some engineering to get the Davis sensor to fit.
« Last Edit: July 27, 2018, 01:35:48 PM by hwcorder »

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #19 on: July 27, 2018, 01:36:03 PM »
Has anyone else tested one of these?

https://www.baranidesign.com/meteoshield-professional/

I've had mine in for about three days and happy with the results. Stats from MADIS have held about the same compared to ASOS station close to me and the last two days have been mostly sunny and fairly light wind. The shield is expensive for a passive and definitely more than the 7714. It's supposedly designed to protect the sensor from contamination in the way airflow is directed inside the chamber.

My problem with it is it's designed for a probe sensor and is completely open at the bottom letting in reflected radiation. I'm thinking of snow albedo and longwave radiation at night, in particular. Plus, isn't it something like $500 just for the shield?
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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #20 on: July 27, 2018, 01:57:00 PM »
Has anyone else tested one of these?

https://www.baranidesign.com/meteoshield-professional/

I've had mine in for about three days and happy with the results. Stats from MADIS have held about the same compared to ASOS station close to me and the last two days have been mostly sunny and fairly light wind. The shield is expensive for a passive and definitely more than the 7714. It's supposedly designed to protect the sensor from contamination in the way airflow is directed inside the chamber.

My problem with it is it's designed for a probe sensor and is completely open at the bottom letting in reflected radiation. I'm thinking of snow albedo and longwave radiation at night, in particular. Plus, isn't it something like $500 just for the shield?

The Davis #07714 has a closed bottom shield plate and was only $54.
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Offline ValentineWeather

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #21 on: July 27, 2018, 02:09:53 PM »
Randy, do you visit Dr Steve Dimse's findU weather site? There, you can overlay selected local sites (yes, more than one) over your plots. For example, here's my DW6988 (blue) overlaid with local Marana airport KVAQ (purple):

https://weather.gladstonefamily.net/qchart/D6988?date=20180727&addnl=KAVQ&Add+to+charts=Add+to+charts&.cgifields=addnl

Nice thanks.

Yes the 7714 are completely closed on bottom someone was a genius when designing or just got really lucky.   :grin:
« Last Edit: July 27, 2018, 04:13:55 PM by ValentineWeather »
Randy

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #22 on: July 27, 2018, 02:14:16 PM »
OK, so doing a bit of research into reference humidity measurement and stumbled onto user's manual from All Weather Inc., the manufacturer of the AWOS system. It mentions using an *optional* aspirated shield for measuring humidity. See: http://www.allweatherinc.com/wp-content/uploads/5190-C-0011.pdf. I'm 99.9% sure this sensor is used ONLY for measuring humidity as temperature measurement occurs in a different shield and requires fan aspiration.

Also interesting is that at -20C (-4F) it's max humidity reading is down to 81%.
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Offline ValentineWeather

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #23 on: July 27, 2018, 02:15:53 PM »
Has anyone else tested one of these?

https://www.baranidesign.com/meteoshield-professional/

I've had mine in for about three days and happy with the results. Stats from MADIS have held about the same compared to ASOS station close to me and the last two days have been mostly sunny and fairly light wind. The shield is expensive for a passive and definitely more than the 7714. It's supposedly designed to protect the sensor from contamination in the way airflow is directed inside the chamber.
Edit: Forgot to add you will have to do some engineering to get the Davis sensor to fit.

Can you get the SHT31 inside?  I was going to be involved with testing these but they never got back after I gave them all information.

I made the mistake of posting a thread here and had a few negative post about persons with no interest in a passive shield and never heard back from them again. 
Randy

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Re: WMO field study thermometer shield FARS 7755, Passive 7714
« Reply #24 on: July 27, 2018, 02:22:19 PM »
Has anyone else tested one of these?

https://www.baranidesign.com/meteoshield-professional/

I've had mine in for about three days and happy with the results. Stats from MADIS have held about the same compared to ASOS station close to me and the last two days have been mostly sunny and fairly light wind. The shield is expensive for a passive and definitely more than the 7714. It's supposedly designed to protect the sensor from contamination in the way airflow is directed inside the chamber.

My problem with it is it's designed for a probe sensor and is completely open at the bottom letting in reflected radiation. I'm thinking of snow albedo and longwave radiation at night, in particular. Plus, isn't it something like $500 just for the shield?

The Davis #07714 has a closed bottom shield plate and was only $54.

See bolded & enlarged part of quote.
Davis Vantage Pro2 FARS | https://marquetteweather.com | EW7933