Cumulus Support

Repairman77 wrote:

keithatrochdale wrote:Repairman77

The aspirated unit should be sufficient for now when it's finished; if the gloss paint on the plastic pot saucers ever dries, LOL.

Mike.

Ahh yes, did you give them a coat of etching primer first?

I use Prymol on plastics - a spin off from my hobby of R/C model aircraft.

keithatrochdale wrote:

Repairman77 wrote:

keithatrochdale wrote:Repairman77

The aspirated unit should be sufficient for now when it's finished; if the gloss paint on the plastic pot saucers ever dries, LOL.

Mike.

Ahh yes, did you give them a coat of etching primer first?

I use Prymol on plastics - a spin off from my hobby of R/C model aircraft.

No, I used some Dulux Gloss White which I had around; intended to give them two coats but not sure if I will live that long.
Have used it on plastic before with good results but it does take a while to dry.

Mike.

Sudden thought -

You guys do realise that if you are going to fan aspirate, you need to have a 'tube' guide ?

beteljuice wrote:Sudden thought -

You guys do realise that if you are going to fan aspirate, you need to have a 'tube' guide ?

Not too sure what you mean by that; or am I being a bit thick?

Mike.

The mix 'n' match problem.

You have a louvered screen (say plant pot saucer style), you put a fan in the top.

How is the air being drawn accross your sensors ?
It is going to take the path of least 'resistance' ie. in / out the nearest vents.

Other way around ...
Your sensor is an open bottom PVC drainpipe with a fan at the top (a perfectly valid design) - how do you encourage natural ventilation / extra 'insulation' if the fan isn't run 24/7 ?
(One answer. put it in a screen )

The compromise ....
Using plant pot saucers example.

The sensors are placed in open bottomed tube with fan at top.
The tube is 'suspended' in the 'saucer' screen. ie. there is an open gap between the tube and the holes in the middle of the saucers.
Top saucer (or two) are used to waterproof the tube exit / fan, and help hold everything together.

There are lots of examples about, but here's a decent pictorial guide (see Mk2 / 3) from Dimitris in Greece.

http://users.otenet.gr/~meteo/project_r ... hield.html

Thanks for the info; a similar design to the Spanish one but enclosing the sensor unit in a tube.
That can be arranged with my design. I'm not using such a powerful fan arrangement as that design but it does give a slow airflow over the sensor.
I did see the shortcomings of not having the tube and having the gaps open and wondered about that.
Will report on progress and any improvements on accuracy once I get it finished.
Mike.

Of course, if you wish to meet all Met Office standards ......... The wheels are so you can move it into a large open area

The beteljuice 'accidental' stainless steel design: PS. I've even put a matt black card sleeve inside the innermost tube.

WOW, some well made pieces of equipment there.
I take it the Mk3 works best?
Mike.

The Mk2 was quite adequate, the extra sleeve made the most measurable difference, to the extent that on one 'maintenance' inspection I discovered a spider had silked up the weak kiddies fan and I hadn't noticed any difference.

It was a going cheap solar light, then I discovered that the sensor wouldn't fit in the luminaire, and the solar panel wasn't strong enough to turn the fan.

So I inverted the luminaire 'cage' to give some radiation protection and outer convection to the tube 'body' which became the container for the sensor.

Much testing with thermometers and positioning and housing showed that in STRONG full Sun it 'suffered' approx, 0.8C So I literally wrapped a baked bean tin around it (temporary test !) and it was perfect

So the tin was replaced by the cheap ss BBQ grill, then when I was 'recycling' a dead PC I upgraded the fan (but had to buy a decent solar panel) ... and so on.

The beauty of the Stainless Steel is that it reflects everything, stays clean, and is slightly better on the eye for Lady beteljuice.
Downside (not for me - I work cabled) is that you would have to solder a wire aerial tail that came out externally to work wirelessly.

It was a couple of years later I realised that I hadn't quite copied a near perfect existing design (Assman psychrometer)

Just in case there are any believers out there - the first picture is a pastiche that I create during a looooong argument on sensor siting (for joe public) on another forum.

Thanks for the extra info.
I can understand the signal being attenuated inside a baked been tin.
I'll try the plastic trays and tube approach first and see how well it works; I have some matched thermometers to check it inside and out.
I guess a lot of people who buy the cheaper WX stations don't know about the errors, especially in sunshine, and take all the readings as gospel. It's only people like us who check the readings against other equipment who would know such errors existed.

Hopefully the solar panel will arrive today or tomorrow. At least the first coat of paint in now dry.

Mike.

If you really want to chase rainbows, something that is rarely mentioned. (anywhere !)

The inside of any screen, and the underside of any louvres should be matt black.

Well most of the construction is now finished; although there was one necessary modification needed. The original motor and fan which I used (which ran at 6V 50mA) was not very effective, so I replaced it with a CPU cooling fan (which is regulated at 9V and draws 100mA). It's far more effective and should do the job. I've found a battery (miniature 12V lead acid type) which should allow 24/7 operation with the solar panel for a charger. Just awaiting the solar panel to arrive, and a few paint touch ups needed.

New aspirated screen has been installed this afternoon, with a lead-acid rechargeable and a small solar panel to charge it.
Not too sure if the panel will charge it on dull days enough to run it all night. I have my doubts.
I may have to resort to feeding 12V up to it from the workshop; no problem as I noticed there is already some twin red and black cable spare which goes from the workshop to the top of the tower which I could utilise.

Now I have to see if it makes any difference. It can't make it worse.
The temperature is the worse one affected; when the sun came out it added around 2 degrees to the actual air temperature.

I notice you have not increased the area of the wind direction sail, this is another suggested modification and it seems to work.

keithatrochdale wrote:I notice you have not increased the area of the wind direction sail, this is another suggested modification and it seems to work.

I did wonder about that Keith, it does wobble about a bit. Probably because it has very light bearings.
Mike.