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Author Topic: VP2 Upgrade Adventure  (Read 20314 times)

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Offline administrator

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Re: VP2 Upgrade Adventure
« Reply #30 on: December 17, 2005, 12:17:41 PM »
I wasn't proposing roof mounting because the readings would be lower (I doubt if an extra 20ft would make a huge difference after the light has travelled through around 100 miles of the Earth's atmophere). The reason for roof mounting is to ensure that they can see the sun as much as possible between sunrise and sunset. I thought the ideal place for mounting a rain gauge was in a reasonably large clearing in a group of trees...which is just the place you wouldn't want to put a solar/UV sensor!
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Offline weatheroz

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Re: VP2 Upgrade Adventure
« Reply #31 on: December 17, 2005, 12:39:18 PM »
I wasn't proposing roof mounting because the readings would be lower (I doubt if an extra 20ft would make a huge difference after the light has travelled through around 100 miles of the Earth's atmophere). The reason for roof mounting is to ensure that they can see the sun as much as possible between sunrise and sunset. I thought the ideal place for mounting a rain gauge was in a reasonably large clearing in a group of trees...which is just the place you wouldn't want to put a solar/UV sensor!
Well I've got my ISS 1.5m above ground on a pole, and even though there's no real shade to speak of, I start to get low UV readings from after 3pm (sunset is around 6:40pm), so you might be fairly safe having them where your rain gauge currently is.
 

Offline daveq

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Re: VP2 Upgrade Adventure
« Reply #32 on: December 17, 2005, 02:48:30 PM »
Just a thought on my part and could be absolutely wrong.  But any site you look at has a bell curve for the graph. 

I don't think it matters how open the area is, as it is the angle the light hits the sensor unless of course it's shielded by trees, buildings or whatever.  When I was testing mine I could see on the graphs where the sensor had been pointed at the sun verses a level position.  I think the only way you could get a true reading would to have a tracking device that kept the sensor pointed directly pointed at the sun at all times (like one of the star tracking telescopes) or a program that would calculate the solar energy based on the time and angle of the sun in relation to the sensor.  But then again what the heck do I know.

--Dave

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Re: VP2 Upgrade Adventure
« Reply #33 on: December 17, 2005, 03:38:15 PM »
The bell curve is probably partly related to the inability of the sensors to operate well at low sun angles. However, even if you tracked the sun, you would still get a bell curve. Solar radiation, including UV, is greater at noon (approx) because that's the time when it's coming through the least atmosphere. In the morning and evening the radiation has to pass through a lot more atmosphere to reach you, so more of it is 'lost' on the way to the sensor. That's why you get sunburn much quicker at noon than at 0800!
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Offline daveq

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Re: VP2 Upgrade Adventure
« Reply #34 on: December 17, 2005, 03:50:54 PM »
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

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Re: VP2 Upgrade Adventure
« Reply #35 on: December 17, 2005, 04:04:52 PM »
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
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Offline daveq

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Re: VP2 Upgrade Adventure
« Reply #36 on: December 17, 2005, 04:14:24 PM »
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
   

Offline niko

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Re: VP2 Upgrade Adventure
« Reply #37 on: December 17, 2005, 04:36:48 PM »
I wasn't proposing roof mounting because the readings would be lower (I doubt if an extra 20ft would make a huge difference after the light has travelled through around 100 miles of the Earth's atmophere). The reason for roof mounting is to ensure that they can see the sun as much as possible between sunrise and sunset. I thought the ideal place for mounting a rain gauge was in a reasonably large clearing in a group of trees...which is just the place you wouldn't want to put a solar/UV sensor!

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.

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Re: VP2 Upgrade Adventure
« Reply #38 on: December 17, 2005, 04:48:53 PM »
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.
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Re: VP2 Upgrade Adventure
« Reply #39 on: December 17, 2005, 04:53:18 PM »
Just a thought on my part and could be absolutely wrong.  But any site you look at has a bell curve for the graph. 

I don't think it matters how open the area is, as it is the angle the light hits the sensor unless of course it's shielded by trees, buildings or whatever.  When I was testing mine I could see on the graphs where the sensor had been pointed at the sun verses a level position.  I think the only way you could get a true reading would to have a tracking device that kept the sensor pointed directly pointed at the sun at all times (like one of the star tracking telescopes) or a program that would calculate the solar energy based on the time and angle of the sun in relation to the sensor.  But then again what the heck do I know.

--Dave

That "bell curve" is exactly what this sensor should produce, it does not measure direct solar radiance which is measured with the sensor tracking the sun, it measures the the radiance on a horizontal surface, which will depend on the angle of the sun.

Offline niko

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Re: VP2 Upgrade Adventure
« Reply #40 on: December 17, 2005, 04:56:09 PM »
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.


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

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Re: VP2 Upgrade Adventure
« Reply #41 on: December 17, 2005, 04:56:36 PM »
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).
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Re: VP2 Upgrade Adventure
« Reply #42 on: December 17, 2005, 04:58:37 PM »
Yes, the console will compensate based on the altitude you plugged in. WD gets the raw value and does its own compensation.

Offline daveq

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Re: VP2 Upgrade Adventure
« Reply #43 on: December 17, 2005, 05:33:45 PM »
That "bell curve" is exactly what this sensor should produce, it does not measure direct solar radiance which is measured with the sensor tracking the sun, it measures the the radiance on a horizontal surface, which will depend on the angle of the sun.
Agree completely.  Sensor on a horizontal plane will and must produce a bell curve.  Sensor pointed directly at the sun at all times without interference will not produce such a curve.  Thanks for the discussion guys!

Back on topic:  Good luck with the VP2 and see the USB version is working for you.  I think that makes two of us. :)
--Dave

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Re: VP2 Upgrade Adventure
« Reply #44 on: December 17, 2005, 06:03:34 PM »

 

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