Cumulus Support

.................... that works with Cumulus and will record W/m2?

The only solar sensor which works with Cumulus and measures W/m2 directly is the one that Davis supply for the VP2. The ones with the solar Fine Offset stations measure Lux, which Cumulus converts to W/m2 using an approximation.

Hi,

I have no "inside information" about the FO Solar Pod, but suspect that (despite FO's reference to Lux units) it actually uses a normal silicon photodiode, which has a response extending into the IR region (as required for a watts/m2 measurement). Also, although it's mounted under a white "diffusing dome" (as might be expected for Lux), the actual response doesn't seem to be too far from the "(co-)sine response" of a typical horizontal "flat plate" collector. The later WH-308x models can be set to display w/m2 (the sensor is obviously the same for both scales) but a previous thread suggested that FO had used a totally incorrect conversion factor!

Therefore (with all the usual caveats about FO quality, accuracy and reliability), the "off the shelf" FO station may offer a usable Solar Measurement of watts/m2 (I have grave doubts about their "UV"). But, particularly as you've posted in the "Homebuilt" section, perhaps you should be looking at the "weatherduino" project. However, I do have some concerns about the particular solar sensor (and circuit) used there, and am looking at an alternative arrangement. But mine is a very slowly-moving project, so don't hold your breath.

Cheers, Alan.

Hi,

This might be a slight digression in context of the original post but from my experience with photodetectors, the only way to correctly measure UV is to use a "proper" UV sensor. The device of choice in industry are photodiodes using the Silicon Carbide substrate with the correct UV filter as opposed to a filtered pure silicon device which has a different response curve.
For those interested at arduino applications and such, the following might be of interest, detector wise.

http://www.sglux.com/fileadmin/pdf-link ... _guide.pdf

The graphs on Page 7 (an excellent illustration of lin vs log plots and why you need to be aware of this) and Page 8 are instructive.

For the record I have no propriatery interest in the company. I've just happened to use some of these devices in the past. Beware, they're not that cheap....

Cheers,
Bill.

Hi,

Thanks for the link Bill. Yes, the minimum 83 Euros price for a "UV Index" diode shows why I am a little "suspicious" of FO's offering.

Also, the application diagram in Appendix A is very similar to the approach I've been using (for my Visible/IR diode data).

Cheers, Alan.

Hi,
I've had a bit of a brainwave....

It would still need some external electronics to do the measuring (an opamp circuit) BUT GaN/SiC blue LED's are now available very cheaply.
One could use really fine emery paper to scar the plastic lens dome to act as diffuser, or even carefully chop it off close to the emitting element then attack it with the emery.

There probably will be some wavelength shift since it's not being used quite as intended but it's still just a diode. Rather than pumping current through it to emit light we're exposing it to bright light to generate some photocurrent. The photocurrent produced will be in response to the diode junction characteristics, and GaN/SiC responds to UV!

Still not as good as a proper UV photodiode but it might very well work (and it's an awful lot cheaper...! ) Still a filtering issue though

Cheers,
Bill.

Hi,

BillW wrote:Still a filtering issue though

Yes, AFAIK the major cost is the sharp optical filter required for the true "UV Index", which has a very strong bias towards the UVC wavelengths (alomost completely cutting the nearer UVA and UVB). I expect there are some cheaper UV detectors available, but IMHO the "UV Index" is a rather "pointless" measurement for a local/amateur weather station.

BTW, I looked at the "recommended" (LMC6001) Op-Amp in Appendix A of the above data sheet. It seems to cost over £10, but perhaps that's quite reasonable because its input (signal) current is specified in femto-Amps. That's one million times lower than the micro-Amps of a typical Op-Amp or diode leakage current !

Cheers, Alan.

Just wondered if this was any help
http://www.instesre.org/Solar/Solar_home_page.htm
May not be the cheapest but all the bits seem to be there.
He does have a list of other kits and parts including calibration http://www.instesre.org/Aerosols/order_form.htm
I am using item 3 on the list to try and make my own sensor hopefully with a uv sensor and soil temp/moisture