I am considering the purchase of a Davis Vantage Pro 2. The 6152 just has a solar shield, the 6153 has a fan aspirated solar shield. With a station that must be sited in the sun for solar power, I have concerns about the accuracy of the temperature sensor. For anyone having the 6152, how does its temperature reading accuracy compare to a sensor mounted in the shade? How about accuracy of the 6153 fan aspirated? Thanks for any information you may give.
N2CSA,
I have the Davis VP2 6153 model and love it! The temperature accuracy is great…
If money is not really an issue for you, then I would recommend getting the VP2 with 24 hour FARS.
Since I’ve never had the 6152 model, I cannot speak for it. I’m sure many others on the forum would be glad to help you out.
Good luck!
–Tim
The 6152 is satisfactory for most hobby weather station purposes. The 6153 temps will be more accurate in high solar radiation environments. If I lived in the AZ desert I would most likely want an aspirated FARS. This Davis Application Note has some radiation shield test results.
The question you need to ask yourself is how serious are you about having the most accurate readings possible? In other words how much is it worth to you to have your temperatures be as accurate as possible on days with full sun? Only you can answer that based on your level of interest and size of your wallet.
I have a daytime FARS I added this winter. So far this year we’ve had some temps in the 90’s and it has tracked well. The sensor unit is in a very exposed location, with intense full sun, and little evaporative cooling from the ground around since it is surrounded mostly by dry land (sage brush and cheat grass, no trees). Graph #2 shows when it was hot a couple weeks ago. The graph shows my station (CW4409) in blue and the nearby automated airport station about 8 miles away in purple (and a line for an average of surrounding home stations in red). There will be some microclimate differences because the airport is in a flat area, and my sensors are at the top of a small hill. The real test will be this summer when it gets hotter and the air is still.
I only started sending to CWOP last fall, so I don’t have a good comparison graph from before I got the daytime FARS, but the first graph shows a day during last fall when it was in the 80’s.
I’d say the VP2 would do fine without any FARS unless you are in a very hot place or a very exposed location. The FARS should do well just about anywhere. I would not put the sensor in the shade. That’s what the radiation shield is for.
Steve
Whether to go passive or FARS is an interesting question. My answer is that it depends whether you see yourself measuring air temperature as a physicist or as a meteorologist. The physicist will always want to measure the true air temperature and will undoubtedly favour the FARS shield. The meteorologist will be more torn because for many meteorologists there’s a priority to maintain comparability with other official temperature records, both current and, especially, historic. And, certainly in the UK AFAIK, the official record still uses a passive screen. Yes it’s a large, high-quality screen but it’s still a passive screen and even the best such screens still tend to over-record air temperature slightly (eg 0.5-1.0
That’s a very good point prodata. I’ve found that putting my shield in the shade resulted in about 1C drop over being in the sun and compared to other official stations seems to consistently create low summer readings (when the temp is in the 30 - 40C range). I’ve also tried fan aspiration, but now I’m thinking of making an extention lead for my temp sensor (V/Pro) and moving it away form the ISS to the most exposed area I have to both sun and wind and using the shield as a passive shield. I feel that would give me the most accurate and precise data, comparable with official readings.
[quote author=prodata link=topic=16565.msg128781#msg128781 date=1148894859]
…And, certainly in the UK AFAIK, the official record still uses a passive screen. Yes it’s a large, high-quality screen but it’s still a passive screen and even the best such screens still tend to over-record air temperature slightly (eg 0.5-1.0
I too fought this question. I purchased the 6152 and found that it performed very well. I did add the Day-time fan kit. This allows a fan to run when the sun is out and it shuts off at night or when the sun is not out, less solar radiation = less need for a fan. For $70 a Daytime fan kit it was a good middle point to get where I wanted to go and not spend the full amount all at one time for the full time fan unit. The kit takes about 30 minutes to put in and I would recommend it to anyone.
Arend
KC0OFZ
Is Australia the BOM still uses the old wooden Stevenson shields.
The thing is if they ever moved to active aspiration, then they would need to setup some kind of correction to make sure that any temp drop due to the active system on hot, sunny and calm days would match the last 100 years of data from the old passive boxes, so there isn’t really much point doing it. Without correction the data would probably show a cooler summer average compared to historic, even if there is a little error in the historic data, that what we have and we are basically stuck with it.
Personally I would really like to find one of those old wooden shields and put my sensor in it. I’de guess that the plastic Davis shield isn’t as good a shield as the official wooden boxes, but probably not far off.