Solar Sensor 2, converting solar sensor volts to W/M^2 Options

[rdheiliger]

I forgot one thing in the last post. Dividing the voltage in the current A/D register by 4096. The resolution of the current A/D converter is .2441 mV. The resolution of the voltage A/D converter is 10 mV.

The statement that one would only be able to see night and day would be wrong when the current A/D converter is used as is the case on the Hobby Boards solar sensor board.

The maximum reading I got with the 390 ohm resistor was about .150 Volts. Dividing that by .0002441 Volts read by the current A/D converter results in about 1000 steps between total dark and full sun.

The formula to get mVolts from the current register is:
(Current register counts)/4096 = (current register volts)
Note: 1/4096 = .0002441

The formula to get current thru the sense resistor
(current register volts)/390 ohms = (sensor current)
Note: asumes a standard Hobby Boards solar sensor

The formula to get solar energy is:
(sensor current) * 1157598 = W/M^2 (solar energy)
Note: the readings for solar radiation taken with a SP1065 meter from edtm

http://www.solarstop.net/edtm/1_solar_measurement.htm

Please read thru the Solar sensor thread for more info on how this was derived.
and a copy of the spread sheet used to calculate the conversion factor.

This post has been edited by rdheiliger: Dec 31 2006, 11:30 AM

[rdheiliger]

I have discovered that a quarz Halogen lamp can be used to calibrate the Hobby Boards Solar Sensor. The attached spreadsheet (excel) has the data I recorded and a description of how the calculations are done.

If you would like a copy of the data and chart in Microsoft Word format, give me your email address.

The data shows a very linear response for the CLD, the non linear section of the chart is above what one would normaly get from exposure to the sun. The quartz halogen lamp also heated the Solar Sensor board and CLD and the higher than normal temperature in that region may also explain some of the non linearty in the higher flux region.

I would appreciate any input from those who use the solar sensor, as to the usefulness of the data.

I would also note that the 390 ohm resistor that comes with the Solar Sensor board is too large to get full scale readings. I replace the 390 ohm resistor with 150 ohms. With the 390 ohm resistor the maximum of .25 volts from the current analog inputs is reached at just above 350 BTU/hr ft^2. This is below the readings one will get on a very clear sunny day.

I should also note that I used a power injector to insure an acurate 5 volts to the CLD and resistor. If one is using parsitic power the readings will vary from those presented in the chart. Verifying the voltage while using parasitic power would be very dificult.


RD

Attached File(s)

 CLD240E_DS2438_Calibration_Table.xls ( 19.5K ) Number of downloads: 77

 

[rdheiliger]

A Microsoft Word document containing the spreadsheet in the previous Post.

RD

Attached File(s)

 solar.doc ( 77K ) Number of downloads: 164

 

[Platypus]

Thanks rdheiliger,

This is great, I have been trying to calibrate my Hobby-Boards Tempertaure, Humidity, Solar sensor for a little while and the only thing missing was to get a real value from the solar.

The effort you have put in is much appreciated and it great that you have shared it with us.

[ksdehoff]

Everyone

I'm trying to apply this equation to my solar sensor and am not following something - hoping someone can explain. In the doc provided, the average multiplier is 549440.86 while the post writeup has the multiplier at 1157598. Two questions - which is more correct and what is the logic behind this multiplier!?

Thanks Much
Ken

Thanks rdheiliger,

This is great, I have been trying to calibrate my Hobby-Boards Tempertaure, Humidity, Solar sensor for a little while and the only thing missing was to get a real value from the solar.

The effort you have put in is much appreciated and it great that you have shared it with us.

I'd like to pose a 2nd question - my understanding of the vsens input is that it is a 10 digit binary value, so 0-1023 valid range. I read today several values in the range -641000,639100 - 20 bit values. Is there some internal transformation occurring I may not be aware of, or is there something else I'm missing!?

This post has been edited by ksdehoff: Aug 19 2008, 10:44 PM

[Dubravko]

Everyone

I'm trying to apply this equation to my solar sensor and am not following something - hoping someone can explain. In the doc provided, the average multiplier is 549440.86 while the post writeup has the multiplier at 1157598. Two questions - which is more correct and what is the logic behind this multiplier!?

Thanks Much
Ken

Be aware that HB use 390 ohms insted of 150 ohms for mesuring voltage, so you are not able to use directly data from document. Soon i make a
java class i will post in forum information how to use it.

[Dubravko]

Ok, I found some more interesting info :

Maximum solar energy flux on top of atmosphere is 1350 W/m2, but at the equator, at sea level, and at noon on a clear day, the solar flux reaching the earth is attenuated to 1,000 W/m2.

All those mean we need to measure max 1000 W/m2 ... I will use documentation from rdheiliger (http://www.cocoontech.com/index.php?showtopic=4072&st=15 and http://www.cocoontech.com/index.php?showtopic=6452) .

[Dubravko]

To finalize formula for HB solar board :

(sensor current) * 1730463 = W/M^2 (solar energy flux)

Vsens/390 (HB resistor) * 1730463 = W/M^2 (solar energy flux)


That mean HB solar sensor may measure from 0 - 1109 W/M^2

That are first step in my task to create Java class , now I have to found over voltage solution for progam part