Weather station sensor protection

Almost two years ago, I added some light and UV sensors to my weather station project. Here are the pictures I took at the time, showing the light level sensor:

A few weeks later, I added the UV sensor.

Two years on, and the sensors failed at some point over the winter. Here they are now:

So, as you can see, I'm in need of advice on ways to rebuild this to be more rugged!

Two problems.

  1. the window is not UV resistant,

  2. moisture got in.

  3. is a matter of choosing a proper box, with UV stabilised material.

  4. is harder. Due to temperature changes the air pressure inside the box changes, sometimes some air will be pushed out, at other times air is sucked in - often with lots of moisture, maybe even rain water. In your case mostly around the wire (wire glands can help improve this), but even the best sealed box may leak over time.

My favourite solution for keeping stuff dry is the inverted bucket design. A few holes in the bottom of the container, leave electronics powered on all the time, the waste heat keeps everything nice and dry. Moisture can't build up thanks to the openings in the bottom.

May also work for battery powered projects that are asleep most of the time.

Slightly random thoughts

Better grade of fasteners, use Stainless Steel and put some sort of lubricant on the threads - aost hardware stores now have St.St. fasteners - or go to a marine supply store if you live near one

Paint the enclosure to help protect from uv

get a small piece of glass from a glass store - I would probably fasten the glass ovev the hole for the sensor window with a combination of 1/16 inch double sided sticky tape designed for mounting windows - then use some UV resistant bedding compound both inside and outside of the tape and on the outside edge of the glass window glop the bedding compound over the top of the glass (unless you are into 3Dprinting and want to make a custom frame) - make sure everything is extra clean

Coat the boards with a conformal coating or maybe just paint epoxy over the boards (except for the sensor) (but for sure up to the edge of the sensor and even under it)

Your box is designed for a rubber gasket to go between the lid and the box. I dob't see one in either the old picture or the new picture.

Paul

I have a light sensor mounted in an upside down jam jar. The lid of the jar is mounted on a bracket on the wall with the jar screwed into it. The cable comes through a small hole in the lid. I suggest not trying to seal the container but leave enough of a gap at the bottom to let any moisture drain out and to let the air pressure equalise.

moisture can be pulled from the cable. it can act like an air duct.
as was mentioned, high pressure and low pressure will make the box breathe.

a hole in the box with a cigarette filter will let it breath and the moisture will reach an equilibrium with the outside air.

as for the screws, no much other than getting brass or a marine grade of stainless. 316L is expensive.
also, plastic screws can be used.

saildude:
get a small piece of glass from a glass store

Window glass may block most or all of the UV, not good for a UV sensor.

wvmarle:

  1. the window is not UV resistant,
  2. moisture got in.

Thanks, Leo. I guess some beginners reading this thread might not immediately figure that out themselves.

Question is, where to get a similar box with UV resistant window? As you point out in a later post, glass blocks a lot of UV, so that's not ideal. Which commonly available materials are UV resistant but also UV transparent? I've heard that mica is a good choice, but where can I find a small project box with a mica window? I don't want to spend a fortune, all the other components are inexpensive.

The other question is, whether to try to seal moisture out, or accept that it will get in and allow it to drain/evaporate.

Paul_KD7HB:
Your box is designed for a rubber gasket to go between the lid and the box. I dob't see one in either the old picture or the new picture.

It was and is there, Paul. Hard to see, but you can see it in the second picture I posted. Its some soft white stretchy plastic material that came with the project box. There seemed to be too much of it, so I pushed it into the slot all the way around and finally cut it to length plus a couple of mm so that the two ends were forced against each other in the slot. It still looks pretty good.

The project box was purchased on eBay for very little money and was described as "weatherproof". I was disappointed that the screws were not stainless, but not surprised, given the price.
s-l225.jpg

s-l225.jpg

Substantial UV light (most of UVA band) does get through window glass, and you can always calibrate your rather primitive sensor to account for that.

But then, what effect did the plastic box window have? Did those measurements mean anything at all?

What do you actually want to measure?

See this page.

Not sure what I wanted to measure to be honest. It seemed an interesting thing to try out, as the sensors were available for easy use with Arduino and inexpensive. I suppose I add hoped to compare the UV measurements to the light intensity measurements from the bh1750 sensor and see what that could tell me about what was going on in the sky. But the two readings seemed to stick to pretty much the same ratio...

This "solar UV index" sensor that does not measure UV light at all.

Instead, it has a visible and an IR photodiode, which together are used to estimate the total solar irradiance and extrapolate the UV from that.

This "two band measurement" approach could in principle be used to estimate the intensity of any other wavelength bands in the solar spectrum.

Since it is used to replace glass in windows,I suspect LEXAN is UV proof.

Paul

There is lots of variation in polycarbonate plastics (some are trademarked LEXAN), and some feature additional UV protection, with coatings on one or both sides.

I've used SUNTUF, which blocks everything shorter than 400 nm and lasts for decades in the sun. Utterly amazing material, nearly bulletproof as well.

Nearly bulletproof as well.

Oh! Did recover OK?

I noticed bh1750 sensors on eBay in this housing. Has anyone used one? Does the dome stand up well to the weather/sun?

I guess I could use an ordinary (non transparent) box, drill a suitable diameter hole in the lid for the dome to fit into and seal around it with weatherproof flexible sealant.

This does not solve my problems with the UV sensor, of course. But at least I can get a light/lux sensor working again. Will have to measure & calibrate for the effect of the dome on light readings.

I tested the sensors shown at the top of the thread. The veml6070 UV sensor seems fine. The bh1750 lux sensor appears to be dead. But maybe it's just it's on-board regulator, so I will try powering it directly with 3.3V.