Author Topic: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD  (Read 17095 times)

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Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #300 on: August 13, 2018, 07:32:50 PM »
The Pro is really looking like the real deal, especially for folks who don't want to mess with a fan (that won't be me).
It's obvious the Pro can handle it's own with a slight breeze, now the "no wind, lotsa sun" scenario is obviously needed for the "are fans obsolete" test. :-"

Think so too. No doubt the big question is how it performs on calm days. 
Randy

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #301 on: August 14, 2018, 12:52:36 PM »
Let's try this test again.

I had to rearrange shields even added a tripod to separate now all 4 are catching approximately same amount of sun exposure from south. The earlier arrangement left the 7714 and FARS in early morning shade.  My bad on setup.

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Randy

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #302 on: August 14, 2018, 01:18:12 PM »
Looks better with all lined up together facing south. We do have a slight NE wind so far making right side shield 7714 on wind direction side and mounted about 6" higher than other shields 5'8" vs 5'. Also running coolest currently.

For wind speeds on this test anemometer is connected to standard meteoshield TX-3 is at 8' elevation just above shields. Ignore the Tx-2 at 30'

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Randy

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #303 on: August 14, 2018, 02:55:29 PM »
Saying this with tongue and cheek, is it possible the Davis shield does read low in low wind like the WMO study said?  The Pro is following airport like they are cloned.  #-o
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Randy

Offline jgentry

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #304 on: August 14, 2018, 03:14:35 PM »
Saying this with tongue and cheek, is it possible the Davis shield does read low in low wind like the WMO study said?  The Pro is following airport like they are cloned.  #-o
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Probably so. The pro shield seems like the solution if you want to replace the FARS, more specifically, the Davis FARS. Planning on getting the pro shield soon.
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Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #305 on: August 14, 2018, 03:23:27 PM »
Saying this with tongue and cheek, is it possible the Davis shield does read low in low wind like the WMO study said?  The Pro is following airport like they are cloned.  #-o
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Probably so. The pro shield seems like the solution if you want to replace the FARS, more specifically, the Davis FARS. Planning on getting the pro shield soon.

I wouldn't do anything yet. Still very early on but I'm seeing pattern already with light winds the 7714 still doing the best and closest to the FARS. It's painted black inside just bottom and very top however with VOC paint which may damage sensor.

The Metoshield standard is really lagging behind I'm trying different sensor heights to no avail so far. 
 
Randy

Offline CW2274

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #306 on: August 14, 2018, 03:29:10 PM »
Saying this with tongue and cheek, is it possible the Davis shield does read low in low wind like the WMO study said? The Pro is following airport like they are cloned.  #-o
Well then, the way I see it is that the Davis is more accurate just for this simple reason; how does a shield make the ambient air cooler than actually is??
Not saying it's not possible, I guess...

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #307 on: August 14, 2018, 03:50:27 PM »
Saying this with tongue and cheek, is it possible the Davis shield does read low in low wind like the WMO study said? The Pro is following airport like they are cloned.  #-o
Well then, the way I see it is that the Davis is more accurate just for this simple reason; how does a shield make the ambient air cooler than actually is??
Not saying it's not possible, I guess...

The design with the triple walls could possibly be making some type of heat exchanger is only thing I can come up with. The outer air scavenging a little heat from inner wall and so forth x2 times. 

Updated the 7714 lowered so comparing at same elevations.
 
All 4 of these sht31 's matched exactly all night within .01 most of time prior to sunrise if anyone wonders.
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Randy

Offline safuser

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #308 on: August 14, 2018, 03:53:29 PM »
Just got A Meteoshield Pro and working on putting in a SHT35.  See thread  http://www.wxforum.net/index.php?topic=34919.0

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #309 on: August 14, 2018, 04:22:49 PM »
With clouds light wind they are pulling together as they should. Standard still a little lag.

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Randy

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #310 on: August 14, 2018, 06:32:16 PM »
Really bad day for testing with clouds, you would of expected these to run closer. The 7714 and Fars ran neck and neck, BUT the money shields  :-(     The shields were not aligned for same exposure until red line.

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Randy

Offline CW2274

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #311 on: August 14, 2018, 06:38:06 PM »
 :eek: So the newcomers were seeing more sun than the two Davis shields before noon? Even after, kinda looks like the 7714 is saying "if it ain't broke, don't fix it. Very interesting...


Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #312 on: August 14, 2018, 06:44:10 PM »
:eek: So the newcomers were seeing more sun than the two Davis shields before noon? Even after, kinda looks like the 7714 is saying "if it ain't broke, don't fix it. Very interesting...

Yes they were exposed more, after 12 noon they all had equal sunshine what little we had. I have too much invested to give up so I've been messing with sensor height inside shields. The standard likes sensor up higher and pro down low from what I've seen so far.
Jerry might have the secret sauce for these if he shares.   [-o<
Randy

Offline CW2274

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #313 on: August 14, 2018, 06:54:33 PM »
:eek: So the newcomers were seeing more sun than the two Davis shields before noon? Even after, kinda looks like the 7714 is saying "if it ain't broke, don't fix it. Very interesting...
I have too much invested to give up
Of course all you testers are ultimately doing this for your own benefits, but don't think that the members here aren't very appreciative of yours and the others time and money spent for the benefit of all interested parties. =D>

Offline dendrite

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #314 on: August 14, 2018, 07:04:15 PM »
:eek: So the newcomers were seeing more sun than the two Davis shields before noon? Even after, kinda looks like the 7714 is saying "if it ain't broke, don't fix it. Very interesting...
I have too much invested to give up
Of course all you testers are ultimately doing this for your own benefits, but don't think that the members here aren't very appreciative of yours and the others time and money spent for the benefit of all interested parties. =D>
I was about to bite on a Pro, but Randy's tests have given me pause.

Many thanks from me as well. I love seeing everyone's experiments.

Offline openvista

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #315 on: August 14, 2018, 07:09:11 PM »
I would not suspect the 7755 FARS shield of running cooler than true air temp. Heat exchangers use heat conducting metal not insulating plastic. The Venturi effect, assuming its more than negligible, would apply to all shields since they restrict air flow greatly compared to the surrounding environment. Think of the aspirated R.M. Young shield and how it compares in size and design to the 7755 with inner and outer chambers. How would that not also suffer from running "colder" than ambient temps?

Given that you fixed the biggest flaw in the 7755 with an AC fan (the stock fan runs less than 1 m/s whereas your fan puts out north of 2 m/s), I'd still suspect that's the reference in this scenario.

 




 
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Offline openvista

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #316 on: August 14, 2018, 07:29:44 PM »
By the way, I elevated the 7714 shield today to 20 feet on an eave mount above my garage (by about 6-7ft). I know, that's not a good comparison to a shield at 5ft, but wouldn't you know it, after that, it ran neck and neck with my FARS (inside the specs for the 31s).

Admittedly today was a mostly cloudy day. Previously, though, during cloudy periods when the passive shield was closer to the ground, it ran warm by at least a degree (if not two) during the day which made no sense other than bad siting. When the sun made an occasional appearance today, both shields ran extremely close with the new arrangement.

Thing is, I don't have a good spot for another shield at 5ft AGL without compromising my main station, which I'm not going to do.

Even though it's not technically a valid test, I will report results once sunnier conditions arrive (maybe tomorrow but more likely Thursday). This may be a decent workaround solution for people with limited siting options and/or a sheltered yard who don't want to bother with a FARS.
« Last Edit: August 14, 2018, 07:51:40 PM by openvista »
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Offline CW2274

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #317 on: August 14, 2018, 07:33:37 PM »
The Venturi effect, assuming its more than negligible, would apply to all shields since they restrict air flow greatly compared to the surrounding environment.
Not that it's a measurable factor to our sensors, but not only, compressed air heats, not cools.

Offline openvista

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #318 on: August 14, 2018, 07:48:40 PM »
The Venturi effect, assuming its more than negligible, would apply to all shields since they restrict air flow greatly compared to the surrounding environment.
Not that it's a measurable factor to our sensors, but not only, compressed air heats, not cools.

I believe the thinking with Venturi is that as a mass of air enters a constriction (inner chamber of shield in this instance), the pressure actually drops as it elongates. And I guess people are assuming that a drop in pressure corresponds to a drop in temperature? If this is true, then someone needs to explain why air expands as it warms and drops in pressure (unless constrained on all sides like in a pressure cooker).
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Offline hwcorder

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #319 on: August 14, 2018, 09:32:56 PM »
The Venturi effect, assuming its more than negligible, would apply to all shields since they restrict air flow greatly compared to the surrounding environment.
Not that it's a measurable factor to our sensors, but not only, compressed air heats, not cools.

I believe the thinking with Venturi is that as a mass of air enters a constriction (inner chamber of shield in this instance), the pressure actually drops as it elongates. And I guess people are assuming that a drop in pressure corresponds to a drop in temperature? If this is true, then someone needs to explain why air expands as it warms and drops in pressure (unless constrained on all sides like in a pressure cooker).

I think you are confusing pressure and density.  As air warms in the open atmosphere its pressure remains the same but it decreases in density and thus expands.  If you warm air in a pressure cooker air will try to expand and take up more volume as the temperatures rise. However since it is constrained like you said its pressure rises proportionally to temperature.

In theory a venturi tube works like this.  As air flows though a narrower section of pipe its velocity increases and as a result its static pressure.  As a result of this pressure decrease you should get a drop in temperature where the pipe narrows.
« Last Edit: August 14, 2018, 09:41:36 PM by hwcorder »

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #320 on: August 14, 2018, 09:47:07 PM »
Looks like other shields got dinged for running cooler also.
Randy

Offline jgentry

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #321 on: August 14, 2018, 10:08:03 PM »
Looks like other shields got dinged for running cooler also.

According to that study, the author thinks the Davis passive is better than the Davis FARS...
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Offline hwcorder

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #322 on: August 14, 2018, 10:58:02 PM »
Looks like I'm may have to buy an extra transmitter and start running my own shield to shield comparisons.  Whats another 100 dollars I guess. I feel like with all the money I've put into my VP2 I could have been half way to my own ASOS by now.  :lol:

Offline ValentineWeather

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #323 on: August 14, 2018, 11:02:10 PM »
Looks like other shields got dinged for running cooler also.

According to that study, the author thinks the Davis passive is better than the Davis FARS...

Followed the reference 97-99% of time depending on wind speed is why. 
Randy

Offline openvista

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Re: Field study thermometer shields FARS 7755, Passive 7714, & new METEOSHIELD
« Reply #324 on: August 14, 2018, 11:35:57 PM »
About the Venturi Effect...

The main point is that if this effect were present during the day, it would be also be present at night since this is a 24hr FARS. Yet we know that, for the most part (with certain exceptions during limited time periods) the temperature measurements from all the shields converge at night.

Not saying the effect isn't real. It's all about where it's happening (at the intake) and whether the effect is negligible or not present at the measurement location. It's probably extremely local and small.

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