Yet Another Stevenson Screen

[Gina]

Finding my round screen doubtful as to it's solar screening effectiveness, I decided to make a larger screen based on the standard Stevenson Screen. Apart from being smaller than a standard screen, the main difference is that I'm using plastic angle to replace wood for the louvres, cutting down on the work required. Also, the roof is two inverted plastic trays - obtained from a "pound" shop.

The plastic angle is 32mm on each side and easily cut into suitable lengths. The framework corner pieces of wood had grooves sawn in the sides to hold the angle pieces. The angle was catered for by using two sets of saw cuts in the wider side of the wood. The narrower side had just one set of cuts with one side of the angle unsupported. To finish off and stop sunlight getting in from the ends, strips of wood were glued on either side.

I have plans of the construction which I'll post later (they need converting). Meanwhile, I have some photos. I apologise for the poor quality of the earlier ones but they give an idea of the construction.

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The screen in position mounted on a post.

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[geoffw]

Gosh you have been busy Gina. I see you have gone for a single louvre design!

[gemini06720]

Gina, nice work.

You now have to standardize your design ... and start production ... you should have an order to a thousand units within a few days...

[Gina]

Gosh you have been busy Gina. I see you have gone for a single louvre design!

Er.. not quite - the angle forms the two louvres. It is set into the 45mm side of the wood columns as shown in the attached diagram. This applies to the two sides and door - the back plastic angle pieces are only held by one side with a single set of saw cuts in the 21mm dimension.

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[Gina]

Gina, nice work.

Thank you Ray

[Gina]

Interior of screen with transmitter unit installed.

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[malc-c]

Looks good Gina,

I need to do something similar for my installation. At the moment it not only gets direct sunlight mid afternoon, it must also pick up radiated heat from the shed roof as it was well over 32c yesterday, and I don't think it was quite that warm

[Gina]

Wow!! That IS warm The new screen is a definite improvement even over my smaller round screen. You could see the times when the sun was out by the temperature plot - now the plot is smoother and pretty close to the real shade value, I believe.

[malc-c]

I agree with you about the traces... the sensor is in shade up until around 13:00 hrs, then in sunlight until late evening, at this time on a day with broken cloud you can see the times the sun shines and when it's behind cloud with the trace zig-zagging up and down.

I'm going to pop into screwfix tomorrow and pick up 8 of those vents and have a go at one of these screens... whilst it may not provide the same result as a met office approved station, it should give a truer reading than it is now... 16:30 and its 33.5C !!!!!! yeah right !

[malc-c]

Just taken a further look at my installation, and I might try re-locating the sensors first before trying to make a screen.

The rear of the shed (see image below) is in shade all the time. There is approx 18" - 24" between the trees and the rear of the shed ( I left this much so I could always paint it with wood stain as required) and the sensor would be in "free air" as both ends of the shed are open so to speak.



I would need to change the cable from the wind sensors to the base unit - would the following be OK

http://maplin.co.uk/Module.aspx?ModuleNo=26077

it's a 4 wire straight through - 10m RJ11 - RJ11 - tad expensive at £8, so might look on the local market, but is a 4 pin OK to use ?

[Gina]

I would need to change the cable from the wind sensors to the base unit - would the following be OK

http://maplin.co.uk/Module.aspx?ModuleNo=26077

it's a 4 wire straight through - 10m RJ11 - RJ11 - tad expensive at £8, so might look on the local market, but is a 4 pin OK to use ?

4 pin is fine. But it looks like that cable has plugs (male connectors) on both ends so you'll need a female to female coupler as well. Just hope you don't pick up interference like I did with an ordinary unscreened cable. Wiring in my own 2 pair screened cable (screen connected to battery negative) pretty much cured it.

[mcrossley]

Gina, you don't need a socket at one end if you replace the cable rather than extend.

[Gina]

Gina, you don't need a socket at one end if you replace the cable rather than extend.

Ah right. I thought you meant to extend it - I misread your post. Yes, replacing the cable is much better

[beteljuice]

Not happy about you positioning your sensor in a 'tunnel' between the shed and the trees - both can be heat sources !

[Charlie]

Not happy about you positioning your sensor in a 'tunnel' between the shed and the trees - both can be heat sources !

While this is technically correct, I'd like to offer a dissenting opinion. I believe the impact will be "in the noise" with this sort of weather station, and the position will be infinitely better than the current location (in the sun). Unless you're prepared to cut down trees and build a Stevenson screen, I think you're on the best path for your location.