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UV sensor for WeatherDuino Pro2 weather station
#41

I've followed this thread for some time and greatly enjoyed the ideas.
I would like to address my first post to the above discussion regarding UV sensors and diffusers; AllyCat is correct in his assessment of the amount of information relating to the optical properties of white PTFE(Teflon (Dupont trademark)). In my business we machine and manufacture components for a weather instrument company and a few years ago they requested that I do some research on the optical properties of white PTFE which we already manufactured for use in their UV/daylight sensor. After many phone calls to suppliers and 2 days on the internet following every lead, the result was dismal- the only possible that looked promising was a research paper which I had to pay for before viewing- an oblique reference to optical properties only.
There is plenty of information for the transparent kind for obvious reasons but none for the white kind for the simple fact that it is not normally used for its optical qualities.
A helpful paper on various aspects of light measurement instrument design, including cosine measurement with PTFE diffusers, can be found at this address;" citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.271.4353 "
(this paper may be mentioned elsewhere in this forum) Whilst this paper is not specifically for UV, much of it is relevant.
For those wanting to experiment with clear hard covers (and their attendant high reflectivity at low angles of incidence), I've purchased several (UV transparent) fused silica discs for a related project from an eBay store called "BJOMEJAG EBUYER STORE" -the discs are not sold on his site specifically but if you open any filter listing and send a message, he should reply with an offer for that filter with the price for the disc.

All the best,
Peter.
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#42

Peter, I am interested to hear how the fused silica discs work out... Please keep us informed... Many thanks for sharing this info...

Mark R
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#43

Hi Peter

Thanks for your research on this matter.
I'm interested too... I like the idea of clear hard covers.



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#44

I was liaising with someone just recently about UV sensors etc and they made the following comments:

"I initially made my UV sensor cover from high quality PTFE due to its excellent optical properties, but my sensor was blind as a bat. Further research uncovers the optical properties are wonderful for visible light right through NIR and up to a couple of thousand nm, however it's about 97% attenuating at wavelengths below about 390nm, which includes all of the UVA, UVB and UVC bands!"

"I ended up getting some 25mm dia JGS1 which is around 95% transmission down to about 205nm. The sensor needed only a tiny little tweek in software for correct the miniscule loss. Problem I then had was that without any diffuser, I had poor angular response. Mechanical frosting of the glass was considered, but sandblasting it leaves a surface that attracts and holds oil and really doesn't behave well outdoors, and is difficult to clean. Laser etching leaves microfissures that are as bad or worse. In the end, I resorted to hydrofluoric acid to chemically etch both sides of the glass. It seems far more weather-stable, and is giving me near-perfect results. I'd urge anyone considering this to be VERY VERY careful of HF, to read up about it very well beforehand, and to take every possible precaution with its handling."
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#45

Here is my UV sensor comparision for today. Green line is fresh Davis Vantage Pro2 UV sensor and two others are UVM30A. UVM sensors have a clear quartz JGS1 lens. Davis diffuser effect is clearly visible. Otherwise UVM30A is not so bad, those two sensors have been outside two years now.
[Image: UV20160621.png]
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#46

Hi Mikko, Hoping that I could ask you a few questions... How small or round is your JGS1 lens..???? Did you source it online, or was it recovered some another 'product' (ie. scrounged)... What sort of enclosure did you come up with..??? Has heat build up been any issue for you in the enclosure..?? Sorry for the hundred questions, and hope you don't mind.. Just trying to get feedback from others, and share and learn....

Many thanks for sharing your info and graphs.

Mark R
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#47

If you look at the enclosure for davis uv and solar sensors they are double skinned with a gap of 5 or 6mm between each "skin" (a tube in a tube)
And the sensor mounted 10mm off the mounting arm. This (according to davis) allows a flow of air between the two skins and keeps the inner relatively cool and therefore the sensor. I have thought about getting such a cover 3d printed (shapeways.com ) but no longer have access to the software to produce an stl file for 3d printing.
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#48

Yes, I'd seen similar. I've been contemplating an IP rated enclosure mounted inside a slightly larger IP rated enclosure, thereby creating an air gap and then allow for some circulation. Just thoughts at this stage, and will be sure to post info and photos when I get to build stage. We're in winter time at the moment, so prob not so high on my list of 100 projects to be completed, just at the moment... But it will eventuate, some day..... So for now, still keep to gather ideas and experience of others. Thanks for the info JT....

Cheers fellas...

M
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#49

A thought, if one narrowed the gap between the skins at the top of the two tubes it would create a venturi, air speeds up, pressure drops, creating a nice continuous flow with less potential for the air flow to stall.
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#50

(21-06-2016, 23:54)JT118 Wrote:  ... but no longer have access to the software to produce an stl file for 3d printing.

JT118
I can produce an stl file for you if you let me know exactly what you want the item to look like.
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