FAO: Vantage Pro 2 Users with Fan Aspirated Rad Shield

[MattH]

Hi.

 

This is for all vantage pro 2 owners out there with the fan aspirated radiation shield.

 

Given the good summer weather this year I have found that with the fan aspirated radiation shield that in direct sunlight the VP2 is over recording temperatures by around 1C to 1.5C

I know this because of verification with another individual who has an official Met Office Stevenson screen very close to my location. Now clearly the ISS should be in an open location away from buildings and other influencing factors (which it is), hence the reason why I purchased the fan aspirated radiation shield because during the summer months the sun shines directly onto the ISS seeing that it is an open space at 1.5m to 2m above a grass surface, but this still doesn't seem to be enough and clearly I don't want to be re-locating the ISS to a shaded area for example as this would create its own problems longer term.

I am wondering whether anyone else has found/discovered this problem with this particular station during summer on days when solar input is significant and uninterrupted?  It's a shame that despite the price and the high quality of the Davis VP2 it still seems to lack the accuracy to cope with direct summer sunshine on to the ISS, even with the fan aspirated radiation shield in full use and I am wondering whether there is a solution to this problem as I can imagine there are a lot of people out there who think that because their fan aspirated shield is whirring away when the sun is shining in summer that the temperature is correct, when in reality it may well not be and could be up to 1C too high.

Any thoughts or comments would be very much appreciated.

Regards,

 

Matt.

 

[4wd]

I had a Vue before and you could see a rise as the sun got lower and penetrated the shield late in the day.
It would be a rare event if this created a higher max for the day though.
I don't notice an obvious problem with VP2 although mine doesn't have the fan.

They sell plenty in the US which generally has far more sun and heat than we do.

You can only do so much with a relatively small enclosure, the sensor is easily taken out and put in a proper screen if accuracy is more important than cost and messing up the garden.

[TonyH]

Think we also have to accept the limitations of our equipment, our sheltered gardens and thus higher readings compared with the open MO sites. As 4wd says the best bet has be a Stevenson Screen for accuracy, used to have one, let it rot away, they are now VERY expensive!

[Storm1968]

Hi I have the VP2 Pro also I have recently put up a Stevenson screen I do not have a fan aspirated system however I have found no real difference in the readings although our back garden is south facing and get very hot, I did think of putting a fan aspirated system in but decided against as the cost far out reaches the benefits in the uk anyway 

 

Geoff

[Storm1968]

 

Hi Tonyh, I made my screen very cheaply I don't think I spent more than £30 and most of that was on paint. 

 

Geoff

Construction of this screen is a 1/4 inch base framed with 2x2 on it's underside the louver panels are constructed from 

bi-folding door (it took 3 doors to make the 4 double panels they were then screwed to the base the 1st roof is made from 1/2 inch ply as is the second roof they are separated by 4 threaded bars and quiet a few nuts and bolts to give it the spacing I used 4 lengths of 2x2 6ft long for the legs these are screwed to the screen with coach bolts then they are intern screwed to 4 sections of angle iron's that have been nocked 3ft into the ground to hold the whole box in place. the whole box was then spray painted black inside and white on the outside then the outside was painted again 6 times to insure it would last in the good old british weather.

 

 

This screen has now been turned so the door is now facing north.

Edited September 19, 2013 by Storm1968

[TonyH]

But your good at woodwork

[reef]

Are you talking about the 24hr FARS or the daytime FARS?

 

I'm running the 24hr FARS on mains power using 3v DC (about 2.6v with resistance) and find it follows nearby Met Office stations almost exactly maxima-wise. At 2.6v the fan spins faster than off the solar panel or batteries alone and avoids the annoying periods when there isn't enough sunshine to charge the batteries (common in the UK, especially in the winter half-year). This works fine for me as the fan is rated 1-3v and moves considerably more air than the 1.9v on full whack off the solar panel. I didn't find much difference at all even before this though.

 

The daytime FARS is a different kettle of fish altogether though, it uses a less enclosed sensor chamber and will not run when the sunshine isn't directly on it and is a little less effective.