Topic: My findings comparing Acurite, Davis Instruments, and Ambient Weather

[CW2274]

Nearby stations may be accurate in themselves but that has no relevance to other stations in the vicinity unless they are sitting on top of each other.

If you're comparing wind or rain, couldn't agree more. Temp/dew/humidity absolutely can in benign conditions. I've studied thousands upon thousands of observations here for the 10 years I've had my VP2 and know exactly what I'm comparing. Is it fool proof, of course not, but if you know what you're doing, it very effective. What do you do??

[CW2274]

You might not.......

Tell me how you...would? so I know.

Just my conjecture. Put them side by side, which will happen eventually, my money's on the ancient, but upgradeable VP2.

You know how many discrepancies margin of error there are in a test like that even being side by side and you think one could make an accurate assessment between the two with that? wouldn't happen. Again you would never notice.

Anyway nice chatting CW we agree to disagree.

Absolutely I do. How do you think things are compared in the first place?
Anyways, yes, nice to debate civilly.

How would you know which is is accurate/correct?

Welp, pretty much the way we all compare our PWS now, known nearby accurate stations, i.e ASOS's, RAWS, and such, extrapolation, and common sense. Of course, more stringent methods are available if desired, i.e NIST traceable sensors.

So in other words you are guessing which is correct by using "nearby" station data?

Yeah, that's it. Like I said to the other guy, what do you do??

[wxthomson]

The OP did a nice job of trying to help newcomers get some information to help them make a decision.
And from the number of downloads of his pdf it looks like he has been successful.

I thank him for all the work he put into it.

[johnd]

The OP did a nice job of trying to help newcomers get some information to help them make a decision.
And from the number of downloads of his pdf it looks like he has been successful.

Well, yes, but a listing of bare facts alone isn't really sufficient to allow users to reach an informed decision. To start with, the facts are not all accurate as the list stands. How can you have a temperature accuracy expressed as a % - that's meaningless? And 'Number of sensors supported including the all in one sensor' certainly isn't 8 for the VP2 - that's the number of wireless channels. Perhaps the 'number of transmitters supported' is what's meant, but that then obscures the fact that eg a full-house 6345 VP2 transmitter could have up to 12 sensors fitted to it.

Second, the list is lacking any interpretation. For instance, beyond a certain point, faster update intervals do not provide any better weather monitoring.The VP2 (in terms of update intervals) is essentially as good as you need in order to deliver high quality weather readings. (OK, maybe it would be nice to have solar/UV at say 10-20sec intervals, but other than that.) Parameters like temperature and RH (and rainfall come to that) just do not change so quickly as to require per second updates.

And it doesn't highlight the difference between intrinsic sensor accuracy and real-world on-site accuracy. For instance, you can have a temperature sensor that was accurate to ±0.01° but if it wasn't in a good shield then it would be horribly inaccurate for measuring air temperature in practice. It's the quality of the shield that typically dominates temperature accuracy. Also, if a sensor transmitter is self-contained (ie self-powered) then it's far easier to locate it with good exposure and hence achieve much better weather readings than if it's tied to eg a power cable.

I'd suggest that the number of downloads reflects the level of interest in this sort of question certainly.

[weatherc]

It's the quality of the shield that typically dominates temperature accuracy.

Can't agree more here. The question is tought why Davis even sell the passive shield then? Its performance are really questionable if it need a fan 6+ months/year even up here in north.

[ValentineWeather]

It's the quality of the shield that typically dominates temperature accuracy.

Can't agree more here. The question is tought why Davis even sell the passive shield then? Its performance are really questionable if it need a fan 6+ months/year even up here in north.

You won't find me using passive shield but if I did I would do so in best shaded area I could find for best accuracy.

Davis even though they sell top quality products (even their plastic stands out against solar deterioration) is also in business for profit so realizing larger portion of market looks at affordability while somewhat smaller portion is looking at best accuracy they offer options for both. 

[openvista]

Well, yes, but a listing of bare facts alone isn't really sufficient to allow users to reach an informed decision. To start with, the facts are not all accurate as the list stands. How can you have a temperature accuracy expressed as a % - that's meaningless?

So VERY true! 

Usually when a percentage is expressed as accuracy there is a reference point like 20C. So at 20C it is within 2% (0.4C). Also, what they don't tell you is that at 0C there could be, for example, a 1C (2F) variance and at -20C a 2C variance and so on. Ditto in the other direction. May not be a linear deviation either. Could jump up at certain points. Obviously that information is missing here. Yet another reason not to trust manufacturers (pre-release) specs.

[CW2274]

It's the quality of the shield that typically dominates temperature accuracy.

Absolutely. For me the best part of the VP2 is it's wonderful aspirated radiation shield. Stick a decent fan in it, and it rivals the best money can buy.

[SnowHiker]

Can't agree more here. The question is tought why Davis even sell the passive shield then? Its performance are really questionable if it need a fan 6+ months/year even up here in north.

Because I believe the passive shield works fine in northern climates like mine when there is almost always a breeze when the sun is shining.  I'd say the wind around here is at least as reliable as the wonderful Davis FARS.

On the very rare sunny hot day when there is no wind, the temperature feels hotter to me anyway, so I'm not going to sweat the slight accuracy a FARS may or may not give you.  Some may argue that the FARS itself artificially effects the temp.  Plus, I want a station that is as reliable and takes as little maintenance as possible and is wireless.

So the passive shield suits my needs better than with the added complications of a FARS, and I'm not going to pretend that my measurements of the weather variables are some great scientific experiment that needs accuracy to the most minute degree. 

[CW2274]

Can't agree more here. The question is tought why Davis even sell the passive shield then? Its performance are really questionable if it need a fan 6+ months/year even up here in north.

Some may argue that the FARS itself artificially effects the temp. 

It does, it artificially makes it more accurate.

[SnowHiker]

Can't agree more here. The question is tought why Davis even sell the passive shield then? Its performance are really questionable if it need a fan 6+ months/year even up here in north.

Some may argue that the FARS itself artificially effects the temp. 

It does, it artificially makes it more accurate.

Wonderful, when I get a few hundred more dollars, I'll go buy one so that I can tell better exactly just how hot I feel. 

Modern weather monitoring is wonderful, no one had a clue how hot it was before the advent of FARS. 

[SnowHiker]

BTW, I understand people wanting to get the most accurate data possible, but I think it may be a disservice to people looking to get a PWS to try to convince them that a FARS is a necessity no matter what climate they live in, and no matter what they intend to use their station for, especially as good as the Davis passive shield is by itself.  OTOH, it is good to make them aware of the option before they buy and whatever value it may have.

I agree that it would be good to take into account the accuracy of each station with the shields and equipment provided.

[CW2274]

BTW, I understand people wanting to get the most accurate data possible, but I think it may be a disservice to people looking to get a PWS to try to convince them that a FARS is a necessity no matter what climate they live in, and no matter what they intend to use their station for, especially as good as the Davis passive shield is by itself.  OTOH, it is good to make them aware of the option before they buy and whatever value it may have.

I agree that it would be good to take into account the accuracy of each station with the shields and equipment provided.

As far as I'm concerned, all should have a fan, at least in the daytime. It's almost impossible to argue that a fan doesn't increase accuracy in light/no wind conditions. It's obviously a personal choice, those that don't care, those that think it's BS, and those that can't/don't want the added expense. Granted, the solar insolation here is off the chart in the summer, so as far as how much better, I've see as much as 5F difference here between my VP2 and the neighbors passive in calm wind.

[SnowHiker]

As far as I'm concerned, all should have a fan, at least in the daytime.

Maybe they should make it a law; even if you live in a moderate climate where the wind blows constantly, and you just use your station to know what it feels like outside, all PWS manufacturers should be required to equip their stations with FARS.

[CW2274]

As far as I'm concerned, all should have a fan, at least in the daytime.

Maybe they should make it a law

For "official" measurements, it is.

[SnowHiker]

As far as I'm concerned, all should have a fan, at least in the daytime.

Maybe they should make it a law

For "official" measurements, it is.

And everyone who buys a PWS is an "official"?

Can you give a reference to this law, who it applies to, and when it took effect?

[SnowHiker]

I don't know about it being a law, but this is what I got from ncdc.noaa.gov:

Surface Air Temperature
Each USCRN station has three thermometers which report independent temperature measurements each hour. These three observed temperature value are used to derive a single official USCRN temperature value for the hour. This single value is sometimes a median and sometimes an average of various combinations of the three observed values, depending on information about which instruments agree in a pairwise comparison within 0.3°C. Each station transmits the three independent observed values; the computation of the official USCRN temperature value is done after these values arrive at NCEI. The discussion below describes the details of the three observed values.

Each station has three Thermometrics platinum resistance thermometers, each of which is housed in its own Met One 076B 7308 aspirated solar shield. Each thermometer measures the temperature (in degrees Celsius) every 2 seconds. Every 5 minutes the station datalogger computes the average of these 2-second values, giving 12 5-minute averages for each thermometer. Standard deviations are also calculated for each thermometer. Finally, a moving 5-minute average displaced 10-seconds at a time is used to determine the maximum and minimum 5-minute periods ending within the hour in question.

In addition to the thermometer values, the station also measures the speed of the fan in each aspirated shield. As the shield's fan rotates, a contact closes and generates a pulse twice per rotation. The datalogger counts these pulses every two seconds. Every hour these 2-second values are averaged to obtain an average number of pulses per second for the hour. The hourly data stream from the station thus include the average pulse rate per second for each of the three sensors. The actual speed of the fan in revolutions per second is half the pulse rate.

So, I assume along with your mandatory aspirated radiation shield, you also have three Thermometrics platinum resistance thermometers, check every two seconds, check the fan speeds, etc., etc.?

If this is the law, you must have a pretty impressive setup, and it's not a Davis.

[CW2274]

I've obviously have you all involved here. "Official" measurements in the US are done mostly, if not all, by ASOS's. To the best of my knowledge, all are aspirated.
Your sarcasm is worthless to the conversation.

[SnowHiker]

Your sarcasm is worthless to the conversation.

Says the PWS cop.

Look, you haven't compared an aspirated shield to a non aspirated shield where I live, you don't have a clue when you say I should be required to have an aspirated shield no matter how I use my station, and no matter how much money I have or wish to spend.  As I've said before, over and over again, I am not interested in the added expense, maintenance, etc., to get what I consider to be a marginal improvement in accuracy.

Sarcasm or not, I am addressing the issue, you just aren't willing to acknowledge other views and needs.  You believe you are a more knowledgeable and superior person for having an aspirated fan, so be it.  I still think both sides should be presented.  I also believe that facts matter, if you claim something is a law you need to be able to back it up, and if you believe one part of the "law" is so important, why not the other parts concerning the equipment used and collection of data?  Call it sarcasm all you want.

[CW2274]

ok

[Mattk]

This fan aspirated stuff is a little over done as there would be an awful lot of "official" stations that are naturally aspirated

[CW2274]

This fan aspirated stuff is a little over done as there would be an awful lot of "official" stations that are naturally aspirated

And you base your remark on what? The current ASOS thermometer is designated the HO-1088, though some older systems still utilize the HO-83, both aspirated.
https://upload.wikimedia.org/wikipedia/commons/c/c3/2013-09-19_09_28_07_ASOS_HO-1088_thermometer_at_Eureka_Airport%2C_Nevada.JPG

[TFD]

Not impressed at all with them specs that the David VP2 has, and for that kind of money!, and you don't even get a fan you have to pay for the upgrade?? 

Really? What are you reading? There isn't ONE thing the Elite does better/more accurately than a VP2, except update a half a second quicker. 

As a retired Broadcast Engineer and an owner of a number of Acurite products including a 5-in-1 outdoor sensor and a 3-in-1 sensor, 2 SmartHUBs, T/H sensors, etc, etc, I feel somewhat qualified to to comment on Chaney/Acurite products.

As you probably know, the ride on the Acurite bus in the last few months has been pretty rough. 2 major outages involving the migration of the Aculink Bridge to a SmartHUB and the latest, Acurite contracting with Amazon for server service along with WU server problems that took Acurite off the WU map for days!

I have tried to help out with around 475 posts on the Acurite forum but to be honest, Chaney has a serious Quality Control problem that doesn't seem to be getting any better. Far too many customers are buying product that is DOA. When customers can't even get a new 5 volt wall wart that works and the fancy color display is defective out of the box, something is definitely wrong.

I would be curious to know if Davis, Ambient, and others are having high failure rates from newly purchased products as well?

Until Acurite can get a handle on this QC problem, I would be very hesitant to invest in the new Elite product line.


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[Mattk]

This fan aspirated stuff is a little over done as there would be an awful lot of "official" stations that are naturally aspirated

And you base your remark on what? The current ASOS thermometer is designated the HO-1088, though some older systems still utilize the HO-83, both aspirated.
https://upload.wikimedia.org/wikipedia/commons/c/c3/2013-09-19_09_28_07_ASOS_HO-1088_thermometer_at_Eureka_Airport%2C_Nevada.JPG

Based on the fact that the majority of "official" sites are in fact naturally aspirated. One could look at this from another angle that anything fan based then has to be "Un-natural"

[BeaverMeadow]

How responsive was Acurite customer service to your quality control problems with the defective power transformer and color display? You warn against the new Atlas Elite but if Acurite addresses hardware issues quickly and honestly then I would still be on board with trusting them to do the right thing when they roll out their new line. I was all set to enter the pws hobby when I heard about the Atlas Elite and decided to hold out and wait till its release. It looks to be a rare new and exciting entry if it doesn't ultimately turn out to be a fiasco (for purchaser and company alike)! 
 

As a retired Broadcast Engineer and an owner of a number of Acurite products including a 5-in-1 outdoor sensor and a 3-in-1 sensor, 2 SmartHUBs, T/H sensors, etc, etc, I feel somewhat qualified to to comment on Chaney/Acurite products.

As you probably know, the ride on the Acurite bus in the last few months has been pretty rough. 2 major outages involving the migration of the Aculink Bridge to a SmartHUB and the latest, Acurite contracting with Amazon for server service along with WU server problems that took Acurite off the WU map for days!

I have tried to help out with around 475 posts on the Acurite forum but to be honest, Chaney has a serious Quality Control problem that doesn't seem to be getting any better. Far too many customers are buying product that is DOA. When customers can't even get a new 5 volt wall wart that works and the fancy color display is defective out of the box, something is definitely wrong...... [/quote]