Author Topic: Building a new Stevenson Screen  (Read 3874 times)

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Offline flyingvranch

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Building a new Stevenson Screen
« on: June 22, 2017, 08:14:22 PM »
I am finally getting around to building a new Cotton Region Shelter or Stevenson Screen for my weather station. The original was destroyed by a severe hailstorm and down burst wind event described here; http://www.wxforum.net/index.php?topic=28433.msg275954#msg275954.
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I am using the same construction that I did previously, building it about the same size and style. The old one served me faithfully for years and hopefully the new one will last as long.
I plan on a few modifications, mainly cementing the legs into the ground and also running PVC conduit for easier wire runs and replacement. I lost my very expensive lab grade thermometers so I don't won't to take a chance on it tipping over, although that last storm was so extreme that I'm not sure that anything would survive that.  :shock: I am also building the double roof a little thicker and bigger so I can mount my rain gauges to it and lastly I am using some industrial oil-based enamel paint to give the slats a little more weather resistance.

I also plan on installing my Davis temp/humidity sensor inside along with the analog glass thermometers just like I did here on the old one;

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The last picture shows the current work in progress and I'll update the thread and post more pictures soon;
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Offline DaleReid

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Re: Building a new Stevenson Screen
« Reply #1 on: June 22, 2017, 10:08:40 PM »
Nice, and thanks for sharing your past event and current effort to get that up for your station again.

I have fond memories of seeing these types of shelters at some national forests and the DNR stations (most built in the rustic and inspiring style of the WPA from the 40s with buildings of stone and grounds that would be far too expensive to recreate nowadays).

I looked at making one and went nuts trying to figure out how to mount the slats.  Are you using commercial made shutters for the ventilation, or cut, route and glue the individual boards?

I know some discussions on the temp inside vs. the radiation shields for the now commercial sensors, and there seems to be a higher temp inside.  Any ideas about maybe putting a FARS type fan on the top to suck air out and let the lower air flow into the structure when there isn't a wind blowing?

Please keep the picture log going and I'm happy to see someone keeping the old style stuff going.
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Offline DanS

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Re: Building a new Stevenson Screen
« Reply #2 on: June 22, 2017, 11:07:20 PM »
  Any ideas about maybe putting a FARS type fan on the top to suck air out and let the lower air flow into the structure when there isn't a wind blowing?


I used to maintain one that had fans mounted in the floor blowing up into the unit and out of the louvers. Measured temps did pretty well too.

Offline Bashy

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Re: Building a new Stevenson Screen
« Reply #3 on: June 23, 2017, 12:23:46 AM »
Hi, the UK MO ones have double louvres and black on the inside nowadays, just food for thought ;) :D



Taken from a write up on one of the longest running WX stations in the world
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Offline flyingvranch

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Re: Building a new Stevenson Screen
« Reply #4 on: June 27, 2017, 11:28:03 AM »
I got a bit more work done the past few days in the workshop.

 To answer a question, I am building this by utilizing a salvaged louvered closet door. We have a Habitat for Humanity resale store nearby and I was able to purchase two doors for $25. I searched for a door that had nice thick slats (1/4"). My previous shelter was built using the same materials but the slats were very thin and they constantly warped in the sun. This door was an older model so the construction was very robust. I was able to cut 6 panels out of the two doors. This left me one panel short so I purchased another door and cut out two more panels. I screwed everything together utilizing pocket hole screws which made the box very rigid. The old box always racked a little and so I made sure to build this one very strong. My cows tended to rub against the old shelter out at the field so I am trying to make this version more cow-proof. LOL Also I plan on enclosing all of the wiring to the shelter in PVC conduit as my calves were constantly chewing on exposed cabling on the outside of the shelter.
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I am going to paint everything before I install the roof as it's easier to reach inside to get into all of the corners. That's all for now and I will post more as I make progress.

Offline DoctorKnow

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Re: Building a new Stevenson Screen
« Reply #5 on: June 27, 2017, 01:39:28 PM »
Bashy is right. You will want to paint the inside black instead of white if you paint it.

Offline flyingvranch

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Re: Building a new Stevenson Screen
« Reply #6 on: June 27, 2017, 02:30:35 PM »
sorry guys but the inside is white. I just finished painting it. The original design was white on the inside and since this is mainly for analog thermometers, I did the same.

Offline Bashy

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Re: Building a new Stevenson Screen
« Reply #7 on: June 28, 2017, 12:51:07 AM »
If it worked ok before for you then it wont make any difference to you, it was just a passing thought
As for the double louvres not quite sure why they started going that route,to me it would restrict
airflow more then sinlge layer but hey ho :) Yours is looking good, certainyl better than the effort
i tried many moons back, i took one pine shelf unit and stuck louvre panels on it :D
Kind regards
Bashy

Offline jpistrit

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Re: Building a new Stevenson Screen
« Reply #8 on: February 28, 2019, 11:09:48 PM »
So i have a couple questions becuase i'm about to build a Stevenson Screen myself.

Looking at this construction i note two things:
 1) the bottom is solid.  Other builds ive seen have the bottom being vented (or slotted).  Does this matter?  (I was planning to go with slotted myself but im wondering if its important)
 2) why would you want the inside to be black rather than white?  Does it matter?

Thank you (and yes i'm a beginner at building weather stations), i'll be "housing" a fully automatic weather station in my screen initially (and maybe getting a set of glass thermometers later so i'm building it about the same size (and also using louvered doors i got to form the sides)

Offline flyingvranch

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Re: Building a new Stevenson Screen
« Reply #9 on: March 01, 2019, 07:17:58 AM »
The bottom floorboards in my screen do have slots of about 1/2" between them but that did not show up well in the photos for some reason. The screen has been mounted and has been living outside next to my ranch airstrip for about a year and a half with no issues. The stand that it is mounted on is about to fall apart and I need to address that. Wasps love to build nest in it.  :shock:

Offline miraculon

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Re: Building a new Stevenson Screen
« Reply #10 on: March 01, 2019, 08:11:07 AM »
Could someone share the theory behind the black interior? Just curious.

Does it facilitate convection through the housing?

Greg H.


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Offline flyingvranch

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Re: Building a new Stevenson Screen
« Reply #11 on: March 01, 2019, 12:46:14 PM »
I've had both black and white interiors and I could not tell a hill of beans difference.  [tup] This one I painted white on the inside and outside as it is much easier.

Offline Bashy

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Re: Building a new Stevenson Screen
« Reply #12 on: March 01, 2019, 01:11:20 PM »
The UK met office have black internals as far as I am aware, I belive there is a scientific reason for it but cannot remember off hand...
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Offline DaleReid

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Re: Building a new Stevenson Screen
« Reply #13 on: March 01, 2019, 04:01:53 PM »
Black body radiation?  Don't know either.

Has anyone put a little fan in the bottom to draw air out or circulate it to make these into a FARS unit?  I know the international standard for such things is likely a Stevenson Screen, but with all the continuous and electronic monitoring, and comparing the to the hundredth of a degree that's being done, would these shelters do a wee bit better to 'reality' if they had a slow pull of air into the box rather than rely upon convection to equalize them?

I'm pretty sure someone must have looked at this.  The problem, of course is the power supply unless you can run line voltage out to the box.

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Offline CW2274

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Re: Building a new Stevenson Screen
« Reply #14 on: March 01, 2019, 04:27:42 PM »
If it matters, the very bottom of the inside of the sensor chamber of the Davis 24hr FARS has a black disc about 3" in diameter where the air first enters the chamber. Perhaps a passive "help" when needed.

Offline the beteljuice

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Re: Building a new Stevenson Screen
« Reply #15 on: March 01, 2019, 07:46:34 PM »
Colour = Reflection = Radiation

Out-side of housing should be gloss white, or a mirror, or even stainless steel !!!!!

This is to reduce the amount of (heat) energy that the housing may absorb due to external radiation.
(It works because 'heat' is at the end of the visible spectrum and a bit beyond)

In-side of housing should be matt black. to 'absorb' any stray radiation.
Think of the design of (water / oil) solar panels.

the beteljuice once converted a stainless steel tube into a housing for a cabled set-up, and took an awful lot of stick from others, until I showed that even when I disconnected a solar fan I had added
it provided more stable results and less 'drift' than anything they had put together.
The 'inside' was simply black card rolled in the tube.

Here are a couple of pics - one next to a 'basin' test design (which failed miserably BTW), complete with unecessary bbq tray additional shield, and bare-bones. (open at base, four vent holes at top)
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« Last Edit: March 02, 2019, 04:39:02 PM by beteljuice »
Imagine what you will KNOW tomorrow !

Offline Bashy

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Re: Building a new Stevenson Screen
« Reply #16 on: March 01, 2019, 11:09:40 PM »
Black body radiation?  Don't know either.

Has anyone put a little fan in the bottom to draw air out or circulate it to make these into a FARS unit?  I know the international standard for such things is likely a Stevenson Screen, but with all the continuous and electronic monitoring, and comparing the to the hundredth of a degree that's being done, would these shelters do a wee bit better to 'reality' if they had a slow pull of air into the box rather than rely upon convection to equalize them?

I'm pretty sure someone must have looked at this.  The problem, of course is the power supply unless you can run line voltage out to the box.



Yes, i had a 12v PC fan, it was out of an old PC PSU but they are all the same except for the larger 120mm ones, it was actually situated in the top between the top of the box and the second skin. it was only added after i found that on calm days the temp would be at least 4C over, but then it was a shoddy build ;) see image, this was main from a pine shelf, i just added louvre door and side panels (cut up louvre doors) :)

Colour = Reflection = Radiation

Here are a couple of pics - one next to a 'basin' test design, complete with unecessary bbq tray additional shield, and bare-bones. (open at base, four vent holes at top)
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Thats what it was, thanks, as for the stainless, i would have sworn blind that all metals get hot in the sun, i thought i best look that up before i start swearing blind, glad i did, moving on....... lol
Kind regards
Bashy

Offline impala454

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Re: Building a new Stevenson Screen
« Reply #17 on: October 17, 2020, 10:37:12 AM »
The bottom floorboards in my screen do have slots of about 1/2" between them but that did not show up well in the photos for some reason. The screen has been mounted and has been living outside next to my ranch airstrip for about a year and a half with no issues. The stand that it is mounted on is about to fall apart and I need to address that. Wasps love to build nest in it.  :shock:

I realize how old this topic is but am curious, is there any mitigation method you use to prevent wasps from building nests in or around your box?  I am building a Stevenson Screen soon and I know wasps love my backyard.  I was thinking about using a very fine wire mesh or something on the inside of the louvered panels but not sure if that affects the readings or not.  Has anyone solved this?

Offline flyingvranch

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Re: Building a new Stevenson Screen
« Reply #18 on: October 17, 2020, 12:21:31 PM »
I had several wasp nests the size of a dinner plate in it this summer. It's a constant problem here, so I would say a screen is a necessity. Other than that it has worked good so far.

Offline DaleReid

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Re: Building a new Stevenson Screen
« Reply #19 on: October 17, 2020, 02:07:24 PM »
Flying Ranch:
If I recall, a curious bovine was a threat for awhile.  Did you move them, or your station, or did they get bored?  I could be mistaken.

Dale
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Offline flyingvranch

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Re: Building a new Stevenson Screen
« Reply #20 on: October 17, 2020, 04:31:41 PM »
Flying Ranch:
If I recall, a curious bovine was a threat for awhile.  Did you move them, or your station, or did they get bored?  I could be mistaken.

Dale

Cows have been moved for now, so no longer a problem with them chewing up my cables. :)

 

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