VP2 Upgrade Adventure

By using Stuart’s program you can see the expected max solar radiation vs the time which I assume takes that into account. So if the sensor was pointed directly at the sun and the expected max radiation was 10 and the sensor saw and read 10 because of no angle to the sensor it would being seeing 100% of the max radiation. The only time you would have less than the expected max would be due to clouds.

So in my feeble mind, on a perfectly clear day with a view from horizon to horizon and a sensor pointed directly at the sun you would never go below 100% thus no bell curve.

–Dave

I think Stuart’s program calculates the time of the maximum solar radiation for each day and the level of radiation expected at that time. The radiation either side of the maximum falls away to zero at sunrise/sunset.

This is shown in the data from an observatory like Mt Teide on Tenerife…http://www.iac.es/weather/otdata/rad_net.html

I’d bet their sensors aren’t pointed directly at the sun. I guess my point is if the max calculated radiation can be measured then no matter the value, even if .001, then 100% because your seeing the max that can be expected at that time.

Didn’t someone on here have a sensor made of 3 solar cells from a calculator because he was trying to get closer to the angle of the sun during the day? I think 180 solor sensors in an array would smooth out the curve greatly.

–Dave

You can extend the cable for the solar sensor, 30 - 40 feet is not a problem. I mounted mine on the (unused) chimney with the anemometer to get it in a clear position. Noise will add some inaccurancy but it should be acceptable relative to the accuracy of the measurement itself.

What shape do you think the daily solar plot would be if the sensor tracked the sun? Maybe I’m misunderstanding what you’re saying. It seems like you’re saying that on a clear day with a sensor tracking the sun you’d get a straight line rather than a curve? Experience suggests that’s not the case. On a sunny day stand in the sun at 0800, 1200 and 1600. You will feel much hotter in the sun at 1200 than at 0800 or 1600 because the solar radiation for the day is at it maximum (approx) at that time.

[quote author=daveq link=topic=13090.msg101228#msg101228 date=1134830910]
Just a thought on my part and could be absolutely wrong.

Right, you would get a different curve due to the changing attenuation through the atmosphere and then some other effects at really low angles.

I’ve made a bit more progress with the VP2 now. I’ve added the USB to serial adapter to the WD PC, loaded up WL and connected the console to the PC. I’ve also put the ISS outside (just sat on a wall for now further away than it will be when it’s mounted) and I’m getting a decent signal from it.

This is about as far as I can go without climbing ladders and drilling walls to mount it properly. I’m going to tray to get that done on Monday or Tuesday.

One final question…I’ve put my height ASL into the console. Does this mean that the console displays SLP rather than local pressure? WL and the console show the same value, but did I read somewhere than WD sees the raw local pressure rather than SLP? The pressure shown by my WMR928 is about 2mb lower than the VP2 and that’s the kind of difference I’d expect between SLP and my local pressure (I’m at around 20m ASL).

Yes, the console will compensate based on the altitude you plugged in. WD gets the raw value and does its own compensation.

[quote author=nikoshepherd

But it’s not as cute as a Cambell Stokes http://www.russell-scientific.co.uk/meteorology/campbell_stokes_sunshine_recorder.html

But it will still produce a curve, just with shallower gradients?

BTW the VP2 is serial…but I’m using a serial to USB converter because the PC only has a single COM port and I need two ports.

That was my opinion a few posts back, I don’t think he is taking the atmosphere into account.

[quote author=nikoshepherd

It will also depend on the construction of the sensor and sensor housing. The sensor may be 3D or if it is horizontal it may be mounted under a lens which focuses any sunlight at most angles onto the sensor. I’ve not seen the VP2 sensors, but the docs suggest they have diffusers which I assume are used to help get light at low angles to land on the sensor?

Yes, no lens, it has a horizontal diffuser, and they expose a little of the vertical edge to enhance the performance at very low angles where the light will be bouncing off the top surface. There’s a good write up on this type of design here http://www.for.gov.bc.ca/hfd/pubs/Docs/Wp/Wp53.pdf

[quote author=nikoshepherd

[quote author=daveq link=topic=13090.msg101306#msg101306 date=1134846905]
You’re correct.

You do. The straight line is effectively the inverse of cloud cover (although other things like pollution could also affect the reading). The maximum number changes throughout the day and if you sensor is receiving the maximum (or very near maximum) then the sky is clear.

I’m glad we all meant the same thing once we worked out what we were saying :lol:

Best of luck with your mounting Chris, nearly got blown off my ladder yesterday with a 30 mph+ gust :frowning:
I’ve not used a UV sensor for insolation, but when doing UV emission spectroscopy our apparatus utilised quartz because glass is a bigger UV absorber.( Have never seen a VP UV detector, so have no idea about it’s structure. )