Author Topic: Is 24hr FARS overkill for me?  (Read 460 times)

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Offline crawdad62

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Is 24hr FARS overkill for me?
« on: August 30, 2017, 02:03:54 PM »
Right now I have an Ambient WS1001. It's set up in a field which is in the sun pretty much the whole day. It never gets shade. I've noticed that my station typically is 1 to 3 warmer than surrounding stations. I had originally thought about getting the Davis VPS Plus without the FARS but since I thought I might want it down the road I figured it was a LOT cheaper to just get it from the get-go. Thing is I live in Indiana where it'll be cool if not cold part of the year. Was getting the 6163 overkill on my part? Realize it's a done deal now. Just sort of wanted some opinions.

Offline dupreezd

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Re: Is 24hr FARS overkill for me?
« Reply #1 on: August 30, 2017, 02:52:52 PM »
@crawdad62, I build this 24 hours shield for my unit and it dropped my daytime temps by about 2F. The humidity readings is also much better in the upper ranges.
Not much improvement below 80 for both temp and hum. Will see what happens in winter.

btw, It just survived 30" of rain during Harvey, however 5 days of no sun and the batteries gave out.  :eek:
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Offline WheatonRon

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Re: Is 24hr FARS overkill for me?
« Reply #2 on: August 30, 2017, 02:59:57 PM »
Right now I have an Ambient WS1001. It's set up in a field which is in the sun pretty much the whole day. It never gets shade. I've noticed that my station typically is 1 to 3 warmer than surrounding stations. I had originally thought about getting the Davis VPS Plus without the FARS but since I thought I might want it down the road I figured it was a LOT cheaper to just get it from the get-go. Thing is I live in Indiana where it'll be cool if not cold part of the year. Was getting the 6163 overkill on my part? Realize it's a done deal now. Just sort of wanted some opinions.

I have the VP2 setup with a daytime fan that I added after the original purchase. I live in the Chicago area. I have no interest in solar or UV readings so got the VP2 instead of the VP2 plus. If I was to do over again, I would have purchased my VP2 with the 24 hour fan already installed. The daytime fan helps (throughout the year) but the solar cell on the 24 hour setup is so much bigger and better than the daytime FARS.

You are right. If you think you might want the feature, save a bunch of money and have it already installed on day one!

I, like many others posting in this Forum, are hoping for a VP3 or whatever Davis wants to call it, but Davis seems to be in no hurry to release a new product. So waiting is not really practical for most enthusiasts!
« Last Edit: August 30, 2017, 03:04:30 PM by WheatonRon »
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Offline ValentineWeather

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Re: Is 24hr FARS overkill for me?
« Reply #3 on: August 30, 2017, 04:55:36 PM »
This question gets raised so much I won't even get into my personal comparisons. Utah State University has one of the longest shield studies fans aspirated vs non aspirated at least 3 years at the university and another remote site called Peter Sink in the mountains.
 
The data is freely available for the public I'll link the current University graphs.  Link:  https://weather.usu.edu/graphical-data/comparethermistorshields

It's always up to the individual what type of accuracy they want with the much simpler low maintenance non FARS shields being the most popular.

Something for the furture Meteoshield is working on a design non fars for Davis sensors. These shields are being touted the next best thing to FARS without moving parts. https://www.allmeteo.com/meteo-shop/solar-radiation-shield-for-weather-station
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Offline CW2274

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Re: Is 24hr FARS overkill for me?
« Reply #4 on: August 30, 2017, 05:34:53 PM »
Thing is I live in Indiana where it'll be cool if not cold part of the year. Was getting the 6163 overkill on my part? Realize it's a done deal now. Just sort of wanted some opinions.
No such thing as far as I'm concerned, but that always seems to start a fight. FARS is meant to quell solar isolation, not heat. I quoted part of the article Randy listed above reference cold climates and FARS.
"At this location we observed the largest difference we have recorded. It occurred on a clear and calm winter day when the low-angle sunlight reflected off the bright white snow went in between the plates on the multi-plate shield and caused it to read 13 C (23.4 F) higher than the fan aspirated shield. These large errors are common in winter and cause our mountain snow melt predictions to have significant errors."
Granted, this sounds like a poor shield design, but take it for what it's worth.
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Offline WxLover16

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Re: Is 24hr FARS overkill for me?
« Reply #5 on: August 30, 2017, 05:51:13 PM »
Right now I have an Ambient WS1001. It's set up in a field which is in the sun pretty much the whole day. It never gets shade. I've noticed that my station typically is 1 to 3 warmer than surrounding stations. I had originally thought about getting the Davis VPS Plus without the FARS but since I thought I might want it down the road I figured it was a LOT cheaper to just get it from the get-go. Thing is I live in Indiana where it'll be cool if not cold part of the year. Was getting the 6163 overkill on my part? Realize it's a done deal now. Just sort of wanted some opinions.

No, no matter where you live I believe some sort of fan is necessary. There will be days where your FARS is needed and you will be glad you went with it.
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Offline crawdad62

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Re: Is 24hr FARS overkill for me?
« Reply #6 on: August 30, 2017, 07:48:52 PM »
Thanks for all the responses. Certainly learned some things =D>

Offline Bashy

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Re: Is 24hr FARS overkill for me?
« Reply #7 on: August 31, 2017, 12:45:47 AM »
This question gets raised so much I won't even get into my personal comparisons. Utah State University has one of the longest shield studies fans aspirated vs non aspirated at least 3 years at the university and another remote site called Peter Sink in the mountains.
 
The data is freely available for the public I'll link the current University graphs.  Link:  https://weather.usu.edu/graphical-data/comparethermistorshields


This is not the best of studies, they are comparing a RM plate shield against a Apogee TS 100 of which is also using a more accurate temp sensor or at the very least, 2 different sensors.

Surely a like for like except for the fan would be a more suitable study,

Air Temperature   R.M. Young Naturally Ventilated Gill-type Radiation Shield   -40 to +60 C   0.01 C   1 C
Air Temperature   Apogee TS-100 Fan Ventilated Radiation Shield                  -40 to +60 C   0.01 C   0.1 C

For a start, the Apogee is in a  league of its own anyway, its what i based my shield on, its insulated for a start
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Offline ValentineWeather

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Re: Is 24hr FARS overkill for me?
« Reply #8 on: August 31, 2017, 01:17:25 AM »
This question gets raised so much I won't even get into my personal comparisons. Utah State University has one of the longest shield studies fans aspirated vs non aspirated at least 3 years at the university and another remote site called Peter Sink in the mountains.
 
The data is freely available for the public I'll link the current University graphs.  Link:  https://weather.usu.edu/graphical-data/comparethermistorshields


This is not the best of studies, they are comparing a RM plate shield against a Apogee TS 100 of which is also using a more accurate temp sensor or at the very least, 2 different sensors.

Surely a like for like except for the fan would be a more suitable study,

Air Temperature   R.M. Young Naturally Ventilated Gill-type Radiation Shield   -40 to +60 C   0.01 C   1 C
Air Temperature   Apogee TS-100 Fan Ventilated Radiation Shield                  -40 to +60 C   0.01 C   0.1 C

For a start, the Apogee is in a  league of its own anyway, its what i based my shield on, its insulated for a start

They use matching sensors. The Peter Sinks site uses two yellow-bead thermistors and two PRTs in an Apogee TS-100 to make replicate measurements.

https://www.apogeeinstruments.com/ts-100-peter-sinks/

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Offline Bashy

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Re: Is 24hr FARS overkill for me?
« Reply #9 on: August 31, 2017, 01:20:16 AM »
I was referring to

Quote
Utah State University has one of the longest shield studies fans aspirated vs non aspirated at least 3 years at the university

Kind regards
Bashy

Offline ValentineWeather

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Re: Is 24hr FARS overkill for me?
« Reply #10 on: August 31, 2017, 01:28:07 AM »
I'm saying the study is using the same thermistors in all shields. Both places at Utah State and Peter Sink same study 2 different locations. Of course the shields are different because one is aspirated.  How does that make the study wrong?
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Offline Bashy

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Re: Is 24hr FARS overkill for me?
« Reply #11 on: August 31, 2017, 01:32:43 AM »
1st off, 1 temp is accurate within 1C the other in 0.1C, second, 1 is a plate shield the other is an enclosed, insulated shield
totally different, surely for a study of this type both shields and temps should be the same, this is really just a Apogee field test
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Offline pfletch101

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Re: Is 24hr FARS overkill for me?
« Reply #12 on: August 31, 2017, 10:00:28 AM »
1st off, 1 temp is accurate within 1C the other in 0.1C, second, 1 is a plate shield the other is an enclosed, insulated shield
totally different, surely for a study of this type both shields and temps should be the same, this is really just a Apogee field test

For a test of shield design, I agree that the sensor probes and associated electronics should be identical. As far as the details of the shields are concerned, though, the issue is a more complex one. If you are trying to answer the question: "Does aspiration result in more accurate temperature/humidity measurements?", you may well want to compare the performance of an aspirated shield that is designed for optimal performance (using aspiration) with that of a non-aspirated shield that is designed for optimal performance without aspiration. Comparing the performance of a shield designed for and using aspiration with its own performance without aspiration is almost inevitably going to "prove" the value of aspiration, but really doesn't address the more general question.
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Offline CW2274

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Re: Is 24hr FARS overkill for me?
« Reply #13 on: August 31, 2017, 03:37:39 PM »
1st off, 1 temp is accurate within 1C the other in 0.1C, second, 1 is a plate shield the other is an enclosed, insulated shield
totally different, surely for a study of this type both shields and temps should be the same, this is really just a Apogee field test
you may well want to compare the performance of an aspirated shield that is designed for optimal performance (using aspiration) with that of a non-aspirated shield that is designed for optimal performance without aspiration. Comparing the performance of a shield designed for and using aspiration with its own performance without aspiration is almost inevitably going to "prove" the value of aspiration, but really doesn't address the more general question.
Good point. The 24hr FARS in the VP2 is a perfect example. It's specifically designed to be aspirated, without, it's a very poor passive shield.
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