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#126348 - 16/08/2002 10:35 Stevenson Screen Design
zan Offline
Junior Member

Registered: 18/07/2002
Posts: 10
I have built two steven screen prototypes:

1. 25cm pot bases painted white, four steel rods and wide cover at the top to minimise sun affects and allow airflow from the top of the screen. Similar to this: http://weather.overflow.net.au/station/stevenson.html

2. Oval shaped 30cm long white plastic plates, two steel rods, with aluminum reinforcement plates. Similar to this: http://homepage.ntlworld.com/martyn.button/start_weather/

When sensors are placed in these screens the temperature ranges from 2-4C higher than a sensor placed on the outside (or next to it). I have allowed enough gap between the plates/pots so you can see through to the other side. A large hole is cut through the middle sections of the plates (i.e. hollow).

When the screens are exposed to sunlight the temperatures inside increases dramatically and can sometimes get as high as 8C between the inside and outside.

Questions:

What is the correct gap to allow between plates when building the stevenson screen?

How can I reduce the temperature variations when exposed to sunlight?

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#126349 - 12/02/2003 12:22 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
My S screen is a little on the smallish side the interior dimensions are 40cm wide 37cm high by 35cm deep, which is pretty deep with the door facing east as I usually only open it in the afternoons or very early in the mornings about 7.00am. I have got the door facing east because I did not want the bulb too close from the west facing wall at the hottest part of the day as it is it 20 centimeters away from the west wall and 5 centimeters away from the south, which never gets the sun.
In the early stages I did have the door facing south and so the bulb was 5cm away from the west wall and it turned the door to the east and it did not appear to make any difference. So those double louvers must be very effective in keeping out radiant heat.


Cheers
Paul :cheers:
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

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#126350 - 16/02/2003 11:20 Re: Stevenson Screen Design
Flame Offline
Junior Member

Registered: 15/09/2002
Posts: 41
Loc: Borden
Is it the screen or the the sensors? Try putting a thermometer in the screen. I have a Kestel 3000 if I stand along side the screen I get a reading the same as the thermometer in the screen. If I put the Kestel in the screen I get different readings.Like the Kestel your sensors may not be calibrated for being in a screen. :cheers:

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#126351 - 18/02/2003 11:54 Re: Stevenson Screen Design
Kirk Offline
Member

Registered: 23/05/2001
Posts: 2239
Loc: Natalia Cooper Fan Club - Pert...
Were can you purchase the screen,
and how much do they generally cost?

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#126352 - 18/02/2003 13:11 Re: Stevenson Screen Design
Kirk Offline
Member

Registered: 23/05/2001
Posts: 2239
Loc: Natalia Cooper Fan Club - Pert...
I am thinking of building the prototype mentioned first. However, how accurate are the readings when exposed to sunlight during the morning.

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#126353 - 19/02/2003 23:04 Re: Stevenson Screen Design
DaveV Offline
Weather Freak

Registered: 19/03/2002
Posts: 196
Loc: Mittagong - Southern Highlands...
If the air is moving at say greater than 5km/h then it may have a small error, say 0.5C - 1C but if it is very still then the margin of error could be greater than 2C.
During the morning this would be less as the suns intensity is lower than it is during the middle of the day, non aspirated screens will exhibit the most amount of error at the hottest part of the day when the sun is directly above and solar load as at its maximum, this though is also very dependent on wind speed.
Here is a link to the specs of a RM young multiplate radiation shield,
RM Yound Radiation Shield

if you look at the second page it shows a listing of radiation errors for particular wind speeds at a specified solar intensity, as you can see the radiation error increases substatially as the wind drops and decreases as the wind increses, if you live in a windy area then this may not be a problem but if you don't then try and protect the screen from direct sunlight as much as you can.
cool

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#126354 - 20/02/2003 22:29 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Mine is just made of old cedar louvers painted white with the internal measurements 40x37x35cm, and I have had it for six years three years at this place.

I have replaced the upper roof about a year ago as it is so exposed to the weather but the cedar louvers are as still good as new.
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

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#126355 - 24/02/2003 00:08 Re: Stevenson Screen Design
Kirk Offline
Member

Registered: 23/05/2001
Posts: 2239
Loc: Natalia Cooper Fan Club - Pert...
Is there a difference in results If i spray painted it white, or if i was to paint it white?

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#126356 - 25/02/2003 16:17 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Quote:
Originally posted by kirk:
Is there a difference in results If i spray painted it white, or if i was to paint it white?
Mine is brush painted with Dulux weather shield gloss acrylic just for durablity but I am not sure if it make any difference
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

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#126357 - 25/02/2003 16:19 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
Nope, no difference, as long as it ends up completely white!

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#126358 - 02/03/2003 22:40 Re: Stevenson Screen Design
---- Offline
Meteorological Motor Mouth

Registered: 25/11/2002
Posts: 5786
Loc: NSW
Long time between posts here......
I made a stevenson screen last year and it works amazingly well. Have a look at the difference between 2 sensors, 1 inside the screen and another unprotected from the sun.
stevenson screen effects
you may need to scroll down to see the images..
Cheers Tim..

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#126359 - 03/03/2003 16:02 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Quote:
Originally posted by hillsrain:
Long time between posts here......
I made a stevenson screen last year and it works amazingly well. Have a look at the difference between 2 sensors, 1 inside the screen and another unprotected from the sun.
stevenson screen effects
you may need to scroll down to see the images..
Cheers Tim..
I did try resting a thermometer outside on a totally shaded area directly beneath the screen a couple of weeks ago one weekend and found no difference between the readings inside the screen and ouside.
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

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#126360 - 04/03/2003 14:05 Re: Stevenson Screen Design
Kirk Offline
Member

Registered: 23/05/2001
Posts: 2239
Loc: Natalia Cooper Fan Club - Pert...
I have now built mine and i am very happy with the readings!

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#126361 - 10/03/2003 22:15 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
Check this Link out, having a good old bash at Melbournes Stevenson Screen. eek eek

http://www.john-daly.com/press/press-02a.htm#surface

Interesed in anyones thoughts. :cheers:

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#126362 - 13/03/2003 17:58 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Quote:
Originally posted by Windy:
Check this Link out, having a good old bash at Melbournes Stevenson Screen. eek eek

http://www.john-daly.com/press/press-02a.htm#surface

Interesed in anyones thoughts. :cheers:
All things considered the Melbourne one does not look all that safe there as it could easily be wiped out in one of Melbourne's many traffic pile ups.
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

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#126363 - 13/03/2003 22:33 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Not to mention during frosty mornings the passing traffic will stir up the air in their wake and will never allow it to settle +the wake of the exhaust fumes which is why it so often records overnight minimums about 2 degrees higher than the surrounding suburbs.
On working week days the effect is even greater because of this.

So the Melbourne one is in a little heat island all of its own.
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

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#126364 - 22/03/2003 20:30 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
This is my screen as it was two years ago but I have since replaced the roof last Chistmas with a lighter one with a double ceiling.

However the readings are usually very consistant with the ones our at the Ballarat AWS, accept in frosty weather as the frosts up here are no where near as severe as the ones at the Ballarat AWS.
I know because there are frost tender plants growing here with should not normally survive in our area.

_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

Top
#126365 - 22/03/2003 22:55 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
Looks pretty good to me, Paul. Are those instruments 1.2m off the ground? wink

Andrew.

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#126366 - 23/03/2003 00:35 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Quote:
Originally posted by Andrew Miskelly:
Looks pretty good to me, Paul. Are those instruments 1.2m off the ground? wink

Andrew.
The bottom one is 1.2m the base is about a little over a meter.
Not as high as this one I think I would need a ladder to read that one
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

Top
#126367 - 23/03/2003 10:53 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
I went out this morning and measured it and it is 1.5m
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

Top
#126368 - 23/03/2003 14:17 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
A retired meteoroligist Gary Bradley told the preferred height for the instrument bulbs was 1.5 meters.
But it happens to be 1.2 meters then I have got it positioned in the lowest and frostiest point in my backyard and even at with to post being 1.3 meters high and bulbs 1.5 meters then the bulbs would only be a meter above the mean hight above most of my house block.
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

Top
#126369 - 03/02/2004 21:40 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Well, I just finished my stevenson screen, all I have to do now is find someone that sells "Wet Bulb" Mercury thermometers and the "Dry bulb" matching type.
Anyone got any ideas where I can get them?



Mick.

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#126370 - 05/02/2004 08:37 Re: Stevenson Screen Design
Helen Offline
Photographer

Registered: 07/11/2001
Posts: 9507
Loc: Mid North, SA
Hi Mick, the only place I've found so far to get the pair is here: http://www.geodetic.com.au/category36_1.htm however I'll keep looking for an Oz site. Taking into account the good $AUD, it'd nearly be worth getting one from the States.

Here's a wet bulb one from Multiquip (an Oz company): http://www.multiquip.com.au/product_all.php?product_id=AO23WA

Cheers, Helen smile
_________________________
2014 YTD - 75.4mm Yearly Average - 403mm
Jan - 9.6mm (10mm) / Feb - 64.8mm) / Mar - - (15mm) / Apr - - (31mm)
May - - (46mm) / June - - (51mm) / July - - (59mm) / Aug - - (54mm)
Sept - - (48mm) / Oct - - (38mm) / Nov - - (23mm) / Dec - - (18mm)
Total 2013 - 348.6mm



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#126371 - 05/02/2004 21:50 Re: Stevenson Screen Design
Keith Offline
Meteorological Motor Mouth

Registered: 16/12/2001
Posts: 6453
Loc: Kings Langley, NSW
This is a shot of my Stevenson screen (from the website page):

http://64.141.102.30/pics9.htm

This was a commercial purchase but it's very robust in design. It looks higher because the ground slopes up a bit and the camera position is low, and in any event is probably higher than it should be. When I contacted some tradesmen I was told it would be very difficult to construct but this one is to BoM specifications.

You might get thermometers from Pegler Beacon in Sydney (Rydalmere I think). They took over Dobbie Bros Instruments in the early 1980s, who used to be the BoM's suppliers.

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#126372 - 06/02/2004 14:37 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
Hi Mick is your's a double louver or single
This is mine it is a double louvered design and it has stood the test of time for about 7 years now and still as good as new, so it is certainly very robust. Those instruments are now set 1.2 meters above ground level. But when this shot was take 2 years ago on a different post and the instruments then set a 1.5 meters above ground level.
_________________________
Rainfall total for 2009: 529.3mm,
Rainfall total for 2010: 747.4mm
Rainfall total for 2011: 804.4mm
Rainfall total for 2012: 654.7mm
Rainfall total for 2013: 493.4mm

Top
#126373 - 06/02/2004 15:55 Re: Stevenson Screen Design
Helen Offline
Photographer

Registered: 07/11/2001
Posts: 9507
Loc: Mid North, SA
Just had a look at the John Daly site only to discover he passed away on Feb. 4, 2004. frown

Helen
_________________________
2014 YTD - 75.4mm Yearly Average - 403mm
Jan - 9.6mm (10mm) / Feb - 64.8mm) / Mar - - (15mm) / Apr - - (31mm)
May - - (46mm) / June - - (51mm) / July - - (59mm) / Aug - - (54mm)
Sept - - (48mm) / Oct - - (38mm) / Nov - - (23mm) / Dec - - (18mm)
Total 2013 - 348.6mm



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#126374 - 07/02/2004 20:13 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Hi Guys,
Well, thank's for the info on the wet & dry bulb thermometers, but I was advised by one of the tech's at the Inverell Research Centre (Where their AWS is based) that for home purposes, a "Fowlers Vacola" stainless Steel Jam and Preserving Thermometer, is as accurate as I'll ever need, so I bought two, one to act as the dry bulb and the other as a wet bulb, with a tube of cotton muslin attached to the bulb and dipped in a testube filled with water, so far it is reasonably accurate for my needs.

Paul2003,
it is only a single louvre setup, not double, I am in the process of getting some more louvres so I can insert another louvre panel inside to make it a double.

I also bought a pushbike digital speedo for my anenometer today, it shows the current speed, average speed, maximum speed on an LCD display, it is programable to whatever circumference wheel you have, so it was perfect for my needs, pity, it cost $60.00, but it seems to be accurate enough, but it won't read a speed lower than 3.0 km/h, but then again, 3km/h is only a slight breeze so it shouldn't matter much anyway, it is the faster speeds I'm interested in.

Anyway, here's some piccy's for you all to look at my work.




Cheer's Mick.

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#126375 - 07/02/2004 23:05 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
Looking good Mick. It's nice to see people having a crack at measuring conditions properly. smile

Andrew.

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#126376 - 10/02/2004 13:44 Re: Stevenson Screen Design
PeterB Offline
Weather Freak

Registered: 04/07/2003
Posts: 409
Loc: Armidale NSW 1000m asl
Hi Mick

Your screen looks good.
Will those thermometers measure tenths of degrees?
Is that your digital wind speed readout at the bottom of the screen or is it temperature?

Peter

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#126377 - 10/02/2004 17:33 Re: Stevenson Screen Design
Blizzard Offline
Meteorological Motor Mouth

Registered: 31/03/2001
Posts: 10264
Loc: Blue Mountains
Mine is pretty basic but does the job. It only gets shade in the morning, pretty much.

http://www.users.bigpond.com/pearcewalker/temp/screen1.jpg
_________________________
BoM Storm Spotter, snow chaser, webmaster for www.blackheathweather.com
Local weather news on Twitter: BlackheathWx

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#126378 - 10/02/2004 19:07 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Here is a link to the programmable bicycle speedo I am using with my anenometer, to find out the wind speed, etc, if anyone is interested.

http://www.bicycle-source.com/cateunii.html

Cheer's Mick.

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#126379 - 11/02/2004 07:32 Re: Stevenson Screen Design
Ray Mullens Offline
Mod Squad, This is my second home!!

Registered: 31/03/2003
Posts: 1223
Loc: Lismore,Goonellabah. Norther R...
Ha Mick :wave:

I got a Speedo from Kmart for about the $50 mark made by Dunlop they also had one there for $20 made by Huffy so there quite easy to come by.
Congrads on the weather station mate great work.

:cheers:
Ray

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#126380 - 11/02/2004 21:19 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
Quote:
Originally posted by Andrew Miskelly:
Looking good Mick. It's nice to see people having a crack at measuring conditions properly. smile

Andrew.
Totally agree laugh laugh , Great work Guys.

:cheers: Windy

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#126381 - 11/02/2004 21:34 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
After viewing F/F's fantastic screen, I have 2 questions to ask.
1- It would seem as though it would be warmer inside the screen than outside, like a confined space out in the direct sun, is this a concern in building a screen?

2- Those 2 Thermometers in F/F's Screen, are they wired up somehow to a display somewhere so you can log Max and Min temps etc?

Keep up the great work guys, those screens look just sensational. smile smile

:cheers: Windy.

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#126382 - 12/02/2004 09:44 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
Windy,

In answer to your fist question, the idea of the stevenson screen is to create a space that's as unconfined as possible whilst still being completely sheltered.

The 4 sides of the screen are louvered and the top and bottom have gaps/holes so that air can flow freely through the box in all directions. The white-painted wood from which it's made ensures that the instruments inside are protected from solar radiation, reflection etc. Most screens are double-louvered which provides better protection of sensitive instruments in windy conditions, and a little more protection from sun etc.

Of course there's probably no scientifically perfect solution but the key is that if all instruments at all stations are in a stevenson screen located in an open, sunny, grassy space then readings from those stations are perfectly comparable.

Here's a few pics I took of the BoM's screen at Taralga PO . It's reasonably well positioned (apart from the missing grass - the pics were taken in the middle of the drought wink ) and I do the obs here on a regular basis which means I can check that the postmaster hasn't planted a tree beside it and give them the odd dig about forgetting to report phenomena and past wx. laugh



Andrew.

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#126383 - 12/02/2004 18:43 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Quote:
Originally posted by Windy:
After viewing F/F's fantastic screen, I have 2 questions to ask.
1- It would seem as though it would be warmer inside the screen than outside, like a confined space out in the direct sun, is this a concern in building a screen?

2- Those 2 Thermometers in F/F's Screen, are they wired up somehow to a display somewhere so you can log Max and Min temps etc?

Keep up the great work guys, those screens look just sensational. smile smile

:cheers: Windy.
Hi Windy,
Thank's for the compliments on my Stevenson screen and other weather equiptment.

Reply to Q1:
Andrew Miskelly gave a far better explanation than I could have, so please refer to his post above, regarding this.

Reply to Q2:
The two thermometers aren't wired for recording the daily maximum and minimum temperatures,that would require me to take readings constantly during the day and since I am away at work all day, that is impossible for me, that is why I have installed an electronic digital Min./Max. Temp and Humidity gauge down below the two thermometers (the white thing below the two gauges in the last page's close up photo) to store that days temps and RH levels, but you can obtain a mercury type, re-settable, outdoor min and max temp gauges (two temp gauges side by side, with resettable slider markers that are left behind once the max or min temp) has been reached, one for minimum and one for maximum) that will record the days min/max temps for around $40 or so from most reputable hardware stores, like Mitre 10, Bunnings, etc. if you have problems getting hold of one, our local hardware store has heaps of them for $43.95, if they are difficult to obtain in your area, (...as I live in a rural town, weather equipment like good quality, accurate temperature gauges and Nylex 1000 rain gauges (the best IMO) are always in constant demand, so they are usually always plentiful and dirt cheap, so if you want anything, just email me, and I'll endeavour to get them for you asap, (plus postage, of course).

Cheer's Mick.

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#126384 - 13/02/2004 18:54 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
Very Impressed eek eek ,
Thanks again guys cool cool .
Great work :wave: .

:cheers: Windy.

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#126385 - 10/03/2004 19:35 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
This screen shows a great view of the double louvre and how the air is able to move freely in and around the screen to provide acurate temps eek eek .


http://weatheroffice.pyr.ec.gc.ca/skywatchers/ontario/wx_office_tour/compound/thermometers_e.html

:cheers: Windy.

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#126386 - 10/03/2004 20:09 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
I'm itchin to build one of these :rolleyes: :rolleyes:

I'd like to try the terrapot saucer one mentioned in the opening post, but I do have some concerns about it being plastic material and it may heat up inside giving a higher than normal temp and with this in mind confused confused , would you be better buying bigger saucers or not? :cheers: Windy.

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#126387 - 18/03/2004 17:23 Re: Stevenson Screen Design
Graham M Offline
Weather Freak

Registered: 21/01/2002
Posts: 291
Loc: Boambee East near Coffs Harbou...
Speaking of max-min thermometers: I bought one once that had a magnetic plate behind the tubes which held the max/min indicators in place, and it was reset by pressing a button which moved the plate back a few millimetres allowing the indicators to fall back to the tops of the mercury. I discovered that this design was flawed, as unevenness in the magnetic plate meant that the indicators sometimes were not held where they should be but moved half a degree up or down to the strong points in the magnetic fields in the plate. I ended up removing the magnetic plate and lying the thermometer down, then resetting it by holding it upright.

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#126388 - 19/03/2004 20:24 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
I think I've made a cheap version smile , does get about 1deg hotter than should in direct sunlight frown , just trying to find the right spot for it confused . Seems to work ok in the garden with my WM918 sensor inside with very comparable temps to my closest weather station cool . Just have to tell my wife to be careful when she waters the garden :p . I will find a more suitable spot for it.

:cheers: Windy




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#126389 - 19/03/2004 20:49 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
Try again, sorry confused confused





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#126390 - 20/03/2004 07:46 Re: Stevenson Screen Design
Graham M Offline
Weather Freak

Registered: 21/01/2002
Posts: 291
Loc: Boambee East near Coffs Harbou...
Here's a quasi-Stevenson screen that I made for someone once for a grand total of a couple of dollars. Plastic plates, cork, wire and glue. You hang it from a tree.

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#126391 - 20/03/2004 11:49 Re: Stevenson Screen Design
Windy Offline
Member

Registered: 13/01/2003
Posts: 507
Loc: Deniliquin, Riverina, Southern...
Very similar to mine, the most expensive part was the paint laugh laugh .

I think if you can find an appropriate spot for these "el cheapos", they can be effective.

:cheers: Windy

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#126392 - 20/03/2004 20:47 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Hi all,
great looking stevenson screen there windy!!!
but I'd place it out in the open rather than under a tree, that way you'd get true temperature readings.

Anyway, I have a question that I hope someone can tell me the answer to.
Considering that we here in Inverell get some very cold winters and it has been known to plummet to -12 overnight so, I was wondering, how do you stop the water from freezing in the container of wet bulb thermometer?
I have a glass test tube that I use to hold the water, that the cotton wick is in, to give the wet bulb temps, and as it is reasonably small and glass, I thought that when it freezes, it would break the test tube as it expand's.
I'd not like it to break, if possible, and I can't seem to find a plastic test tube, so does anyone have any ideas?
I'm sure there has to be a easy solution.

Cheer's Mick.

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#126393 - 21/03/2004 09:51 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
Quote:
Originally posted by Fotoflash:
How do you stop the water from freezing in the container of wet bulb thermometer?
You don't. You can't add any sort of anti-freeze for example because you'd change the evaporative properties of the water.

Andrew.

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#126394 - 23/03/2004 20:27 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Hi Andrew,
yes, I sort of guessed that you couldn't put anti-freeze (Glycol) into the water as it would change the evaporation rates, so how do they address this problem in snow prone regions like the Alpine areas of NSW, etc? or have they devised another system of measuring the wet bulb thermometers in those locations? or don't they bother at all?
I'm very interested in a reply.

Cheer's, Mick.

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#126395 - 23/03/2004 22:35 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
As far as I know there's simply nothing you can do. If the water in the muslin, wick or jar freezes then that's that. This no doubt is as common elsewhere as it is for you and indeed at our BoM station at the PO. We use a robust plastic jar with a loose-fitting lid so that if ice forms it has plenty of room to expand without damaging the jar.

AWSs of course use electronic hygrometers which I imagine are largely unaffected by freezing temperatures.

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#126396 - 23/03/2004 22:48 Re: Stevenson Screen Design
TrenthamStormchasers Offline
Meteorological Motor Mouth

Registered: 15/04/2001
Posts: 6258
Loc: Trentham 705m
I asked the same question of a friend on the Great Lakes who is a met at Duluth and was told that "Once the temp reaches 0C we put a piece of snow or ice against the wick of the wet bulb and then use either the sling phsychrometer or battery operated Psychro-dyne Instrument to get the wet-bulb reading. With the old instrument shelters that we had before the wet and dry bulb could be read much lower. Adequate ventilation across the wet-bulb is essential for accuracy. Without it a moisture concentration not representative of the ambient conditions will build up around the wet-bulb and one will always tend to measure a higher humidity level than what is actually in the air. Ventilation removes the build up and keeps sampling the actual conditions. 10 ft per second or more of air flow is essential for accurate results."

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#126397 - 23/03/2004 22:50 Re: Stevenson Screen Design
temp trace Offline
Member

Registered: 03/02/2001
Posts: 457
Loc: Newcastle, NSW
G'day Mike,

Procedure is as follows,

Carry out the following procedures if the wet bulb temperature is lower than 0C:
(a) Visit the screen at least fifteen minutes prior to the time for making the
observation;
(b) If there is little difference between the dry and wet bulb readings it may
indicate that the muslin has dried-out owing to the water in the wick freezing
and impeding the capillary action;
(c) If a frozen wick is suspected wet the muslin with ice-cold water applied by
means of a squirrel hair brush or a match. After wetting the wet bulb muslin
the temperature will remain steady at about 0C until all the water on the muslin has frozen.
The temperature will then gradually fall to the true wet
bulb value; then
(d) Read and record the temperatures of the dry and wet bulb thermometers when
the wet bulb reading reaches its minimum value.
Note: It is essential that when the wet bulb temperature is less than 0C the muslin
is coated with a thin layer of ice. After the application of water to the muslin
the wet bulb reading may fall well below 0C, yet the water will remain
liquid. This super-cooled water must be induced to freeze by gently touching
the muslin with a match or pencil. At the instant of freezing the thermometer
reading will rise to 0C and then gradually fall. When it ceases to fall the
true wet bulb temperature is indicated.

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#126398 - 24/03/2004 21:10 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
...thank's Andrew, Jane and Temp trace for your help and replies.
I've decided to look for a plastic test tube of similar size, or similar type of device (I was thinking of a plastic 100ml hyperdermic syringe of similar size, and just blocking the needle end off with some hot melt glue, should do the trick, what do ya reckon?), I should be able to find something like that at my local chemist's.
The only reason, I'm using a glass test tube is I bought a wet bulb thermometer that came with a test tube, already attached, from a friend who raises free-range chickens and he use's them in his egg incubator to get the eggs to hatch. The theroy is to maintain a certain range of humidity so the chicks can break out of the shells easily, and not exhausting themselves trying to get out and then dying from exhaustion.

I'll sort the problem out, I'll tell you what I've come up with later.

:cheers: Cheer's Mick.

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#126399 - 24/03/2004 21:23 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
Quote:
Originally posted by temp trace:
After wetting the wet bulb muslin the temperature will remain steady at about 0°C until all the water on the muslin has frozen. The temperature will then gradually fall to the true wet bulb value...
This is interesting. Can anyone expand on the physics behind the second bit? I'm familiar with the temperature of wet ice being 0° but why is the correct wetbulb temperature reflected once it has dried (such that the bulb/muslin is coated with ice if I've read correctly)? I'm guessing there's a link between the freezing process and the liquid's ability to evaporate, which would make sense.

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#126400 - 25/03/2004 21:14 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
I'm not too sure about that, andrew, maybe it has something to do with kelvination? or supercooling the water? I'm guessing really !!!
Maybe we should ask Dr Karl on Triple J, he'd know or at least he'd put us in the right direction, huh.

Mick.

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#126401 - 03/04/2004 20:14 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Hi All,
I've been searching the Internet and the Weatherzone forums for Official BoM Stevenson screen construction plans, I thought there was a set of plans on this page to download, but they seem to have been taken off, does anyone know where I can get a copy of them, so I can print them off here at home?
I have found the BoM site here for making a stevenson screen, but the plans are not for double louvred stevenson screens, only a screen that seems as if it is constructed from "Pin Board" masonite.
I'm just curious as to how they are built, and how much work is involved in constructing an "Official" one.

Cheer's, Mick.

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#126402 - 04/04/2004 00:15 Re: Stevenson Screen Design
Rainlover Offline
Member

Registered: 12/02/2002
Posts: 4421
Fotoflash,

This page may be of some help

Rainlover

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#126403 - 01/09/2004 01:46 Re: Stevenson Screen Design
Christopher Offline
Junior Member

Registered: 01/09/2004
Posts: 4
Loc: windsor
Quote:
Originally posted by zan:
I have built two steven screen prototypes:

1. 25cm pot bases painted white, four steel rods and wide cover at the top to minimise sun affects and allow airflow from the top of the screen. Similar to this: http://weather.overflow.net.au/station/stevenson.html

2. Oval shaped 30cm long white plastic plates, two steel rods, with aluminum reinforcement plates. Similar to this: http://homepage.ntlworld.com/martyn.button/start_weather/

When sensors are placed in these screens the temperature ranges from 2-4C higher than a sensor placed on the outside (or next to it). I have allowed enough gap between the plates/pots so you can see through to the other side. A large hole is cut through the middle sections of the plates (i.e. hollow).

When the screens are exposed to sunlight the temperatures inside increases dramatically and can sometimes get as high as 8C between the inside and outside.

Questions:

What is the correct gap to allow between plates when building the stevenson screen?

How can I reduce the temperature variations when exposed to sunlight?

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#126404 - 01/11/2004 22:22 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
I completed a shelter based on the rather well known (and very ingenious) design here a few weeks ago. I made three key modifications.

  • I used conduit as spacers between the saucers so that the whole unit comes apart in 60 seconds flat.
  • I drilled several holes in the top and bottom saucers to emulate a stevenson screen and allow vertical airflow.
  • I added a timber roof.

It's currently in use logging temperatures for a friend who is interested in grape growing which means that I haven't had time to do a comparison with a real stevenson screen yet but initial indications of its effectiveness are extremely promising.

Here's a few pics.


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#126405 - 02/11/2004 02:39 Re: Stevenson Screen Design
Sonde Offline
Weather Freak

Registered: 27/03/2003
Posts: 279
Loc: Clemton Park 2206
http://www.theweather.com.au/uploads/stevenson1.JPG
----------------------------------------------------
http://www.theweather.com.au/uploads/stevenson2.JPG
----------------------------------------------------

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#126406 - 02/11/2004 11:52 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
Hey Andrew,

Looks like a very well thought out design for your friends screen, I like it.

I just thought of something.....

The roof you've put on could be made out of a large white Nylon chopping board, that way, it would be totally waterproof (as even marine grade (formplex) Plywood isn't totally waterproof, just water-resistant) and UV stabilised, as well as it would cut down on having to re-paint it every now and again, making it a robust screen rather than a high maintainence screen like the wooden one I have, also, Andrew, it seems, by the photographs you have posted, that you have used "chipboard" for the timber, bad choice of timber there, as "chipboard" is not water resistant, and it will swell up to twice, even three times it's thickness with the first bit of rain or high humidity you get, the chipboard is glued together using only the cellulose or sap that naturally occurs in the woodchips when it is green, and it dissolves away in water or rain, leaving the chips to fall apart, the same goes with HMR (Higly Moisture Resistant) chipboard and MDF (Medium Density Fibreboard, otherwise known as CSR "Craftwood"), the only two timbers to use in outdoor or wet area applications are real wood or Marine Grade Plywood (formplex) as they are designed and manufactured to handle the moist conditions of outside applications, as long as the raw edges are sealed properly with a silicon based sealant like "No More Gaps" before painting, as the moisture will get into the timber and start it to swell up also, therefore shortening the practical service life of the timber roof.

.....just a word of warning to those who have made a wooden stevenson screen, don't use spray white gloss enamel paint to paint it, use a gloss outdoor Plastic (acryilic) paint like "Dulux Weathershield" or similar, as I had done earlier, as the paint can not handle the expansion and contraction of the wood, as it cracks and peels off, it might have been easier to apply, but it hadn't even lasted 3 months, the outdoor paint wasn't cheap ($20 for 1 litre) but it is worth it for the durability.

:cheers:

Mick.

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#126407 - 02/11/2004 12:19 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
P.S, thank's guys for the links to the Stevenson screen construction plans, but they aren't the designs I was after, as I had found that particular design previously, not to worry, I'll find it one day, when I do, I'll post a link up for you all.

:cheers:

Mick.

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#126408 - 02/11/2004 12:24 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
.....sorry, Andrew, on closer inspection, it seems as if you have used Marine Grade Plywood (formplex) for the roof, my mistake shocked , still, I hope others wishing to construct a stevenson screen heed my warning about using other types of timber boards for that particular application.

:cheers:

Mick.

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#126409 - 02/11/2004 17:56 Re: Stevenson Screen Design
Andrew Miskelly Offline
Weatherzone Webmaster

Registered: 15/11/2001
Posts: 3117
Loc: Mittagong, NSW
I've done no such thing! The roof is an old bit of cupboard or something. wink

The purpose of building this shelter was to see how well the design works, quickly and cheaply. If it proves successful then a more robust roof will be warranted.

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#126410 - 03/11/2004 21:59 Re: Stevenson Screen Design
Nullamanna WX Offline
Weatherzone Addict

Registered: 09/06/2002
Posts: 1274
Loc: Nullamanna, Nth-West Slopes, N...
My apologies, Andrew, for any misunderstanding regarding the roof material wink .
Still, it looks as if it will be a very robust design, I hope it proves itself in time.

:cheers:

Mick.

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#126411 - 28/04/2005 11:31 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
The thread "Remote Sensor" has more about these "Stevenson Screens".
_________________________
Data are cheap; information is expensive!

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#126412 - 01/05/2005 13:04 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
A bit of history of the use of official Stevenson screens in Australia:

http://www.abs.gov.au/ausstats/abs@.nsf/0/e4d19a717ba99a65ca256f7200832fd6?OpenDocument
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#126413 - 01/05/2005 13:06 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
_________________________
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#126414 - 23/05/2005 19:15 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
My Stevenson screen is not satisfactory. I am moving to a Mark II. If anyone is thinking of following my detailed description in the "Remote Sensor" thread, I suggest they hold off for a bit.

There are several problems, but two are obvious.

1. The screen is too heavy. The pot saucers I used are rather thick, with reinforcing ribs. I also did a lot of filling. The weight is about 4 kg. Although a standard wooden Stevenson screen would be heavier, it is also much larger. The mass of air inside, or passing through, must be large compared to the mass of the screen structure. If the structure has too much mass, I think it heats too much by day by solar radiation (even if painted white), and cools too much by radiation to the sky at night. At night the white paint does no good at all, of course.
I am fairly sure that the daily temperature range recorded in this screen is anomalously high. I am NOT in a frost hollow!

2. The screen is a terrible water trap. This is despite my efforts to make it shed water. There are dozens of places where there is not enough slope, and my attempts to apply filler have formed actual hollows. I painted using a brush, and water refuses to run off the brush marks. Overnight dew keeps the screen wet all day. When I tipped the screen over to work on it, water poured out from somewhere inside.

Back to the drawing board!
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#126415 - 23/05/2005 19:30 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
This forum thread has discussion on trying to make surfaces (such as Stevenson screens) shed water:

http://www2b.abc.net.au/science/k2/stn/newposts/1676/topic1676022.shtm
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#126416 - 10/08/2005 18:18 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
I have collected some information on various types of non-aspirated thermometer screens that are in use. Such screens are known by other names, such as "radiation shields" and "shelters", making them hard to research.

The Stevenson screen is known in parts of the US as a "Cotton Region Shelter":
http://www.wrh.noaa.gov/mtr/cpm/crs.php

A modern thermometer radiation screen modelled on the Stevenson screen is the Metspec screen:
http://www.axystechnologies.com/pdf/products/Metspec_Brochure.pdf
It has a powder coated aluminium frame, and a floor and roof of UPVC. Louvres are of premium grade acrylic (PMMA) with added UV stabilisers. Interior louvres are coloured black, following UK Met Office tests showing improved radiation shielding.

A cylindrical screen about 200 mm in diameter is widely used in the US National Weather Service "Maximum-Minimum Temperature System" (MMTS). It is known as a "beehive". I cannot find good information on it.
Picture here:
http://www.geocities.com/larryhuff1943/temperature.html

The Gill radiation shield, described by G C Gill in 1979 is a small screen only 120 mm diameter, intended for use on ocean buoys. It is made by R M Young.
Cross section diagram:
http://www.campbellsci.ca/CampbellScientific/Catalogue/41301-5.pdf

I suspect that the Davis, Lacrosse, and other home weather station screens are modelled on the Gill radiation shield. I would be grateful if people who have these stations would say if their screens are like the one in the cross section diagram.

The loganvillageweather flower pot saucer screen that I copied is a bit like the MMTS screen.
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#126417 - 11/08/2005 13:06 Re: Stevenson Screen Design
Stephen-wx Offline
Weatherzone Addict

Registered: 15/07/2002
Posts: 1313
Loc: Oak Flats, Illawarra, NSW
I painstakingly put together a balsa screen last year and once it was up and running it proved to be rather accurate. The temp was always within .2c of my closest AWS which is pretty damn good.

That screen is now in shambles lol it was bound to happen and I have a new GE temp and humidity monitor to go into a flower tray design screen. I have been able to get the gap sizes worked out to be as wide as possible without letting light in and it has turned out a rather compact size. Given I have a massive backyard and my last screen was not all that big, fingers are crossed this should be successful.

Some rather interesting screen designs floating around thats for sure.

Stephen smile
_________________________
Stephen Jarrett

my home AWS site: http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=INSWOAKF3


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#126418 - 11/08/2005 18:06 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Steven, I have now commissioned a new screen about the same size as the loganvillageweather flower pot saucer screen that I described in the Remote Sensor thread.
It is made of giant mixing bowls, and I think it will be much better.
I intend to describe it when I have a bit more data.
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#126419 - 12/08/2005 12:51 Re: Stevenson Screen Design
Stephen-wx Offline
Weatherzone Addict

Registered: 15/07/2002
Posts: 1313
Loc: Oak Flats, Illawarra, NSW
Surly sounds very good, looks like my screen is reading too high with the sun on it, being one that loves electronics I'm going to get a solar panel and fan wink

time for some forced exhaust laugh I reckon this should remedy the problem. I'll keep you all posted on how it turns out.

Stephen
_________________________
Stephen Jarrett

my home AWS site: http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=INSWOAKF3


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#126420 - 12/08/2005 19:56 Re: Stevenson Screen Design
Ozzroo Offline
Weather Freak

Registered: 12/08/2005
Posts: 153
Loc: Spring Mountain, Queensland
I am also another with the now famous potplant design. I have made an easy access top and used conduit for spacers rather than bolts and washers. Have tested the screen in the heat of the day with a reliable thermo sitting in the sun. The variation from the thermo inside the screen to the thermo getting hit from direct sunlight was around 7-8 degrees.
_________________________
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http://www.primagicproductions.com/weather/

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#126421 - 12/08/2005 21:03 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Stephen, it sounds like you are going for an artificially aspirated screen. You say it should remedy the problem. I think it actually gives a different result. I agree that it seems to be closer to the ideal of a measure of air temperature free from bias due to very local solar radiative heating.

The problem is that the public perception of "air temperature" is based on measurements from hundreds of thousands of unaspirated screens. On sunny calm days they all over-read quite a lot. If you tell people your aspirated screen shows the air temperature is not as high as they think, they may say that your result is wrong.

In my own case, the bigger the daily temperature range I can observe outside my house, the better the performance of the house appears to be. (The indoor temperature rarely goes outside the range from 16 deg to 29 deg.) To avoid a charge of cooking the books, I must be careful to avoid defects in my outdoor thermometer system that would exaggerate the severity of the climate. However, I do not feel obliged to make my results less impressive by using an aspirated screen, since very few people seem to do so.
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#126422 - 12/08/2005 21:26 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Ozzroo, I have done the same experiment myself. The thermometers I used are the ones in the thread "Wireless temp sensor hints".

I got temperature readings on the exposed thermometers about 10 deg higher one calm sunny day. It is a bit hard to theorise about what is going on though.
When exposed thermistor thermometers in black cases got 6 deg hotter than the one in the screen, one in a white case got only 2 deg hotter.
By chance, I had the air vent in the thermometer cases facing away from the sun. Each thermometer was sensing the temperature of its case, rather than either that of the air or that of a tiny surface facing the sun.
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#126423 - 12/08/2005 21:40 Re: Stevenson Screen Design
Ozzroo Offline
Weather Freak

Registered: 12/08/2005
Posts: 153
Loc: Spring Mountain, Queensland
Surly,
With my screen, I also made sure that there were holes in the base of the unit to allow for extra ventilation. The screen itself is mounted 1.5 above ground on a kopper log. Works a treat. I think with some of the thermo's the case colour would surely make a difference.
_________________________
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http://www.primagicproductions.com/weather/

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#126424 - 13/08/2005 22:11 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Ozzroo,
I have doubts about whether holes in the floor of the screen do any good. I have not used them in either of my screens.
The screen must not allow radiation from any warm surface to shine on the thermometer. The gills or louvres around the sides let air in but keep radiation out.
Holes in the floor, it seems to me, cannot let air in without also letting in radiation.
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#126425 - 14/08/2005 00:39 Re: Stevenson Screen Design
Rime Offline
Weatherzone Addict

Registered: 07/06/2001
Posts: 1443
Loc: Perth,WA
SB,

Holes in the floor are generally required in most gill and stevenson screen designs. The holes allow for greater circulation within the screen and also helps to drain any excess of water. Radiation only effects the readings when sunlight is getting into the screen. If the holes in the floor are out of direct sunlight, then the holes will not have any effect on the readings.

cheers,

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#126426 - 14/08/2005 23:04 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
I have found a URL which this system rejects, but you could find it using google.

It is the abstract of a paper "Some Perspectives on Recent In Situ Air Temperature Observations: Modeling the Microclimate inside the Radiation Shields"
by Lin, Hubbard, Walter-Shea, Brandle and Meyer. It is one of a series of papers reviewing the performance of thermometer screens.

The abstracts are on the net, but the papers cost about $40 each, so I haven't bought them.

This one compares four screens:
Automated Surface Observing System (ASOS)
Maximum-Minimum Temperature System (MMTS)
Cotton Region Shelter (CRS)
Gill shield (Gill).

They say that in the US National Weather Service the CRS is being replaced by the MMTS, and the ASOS is being introduced. Gill shields are widely used by others. The ASOS shields are artificially aspirated, the others not.

"All of these systems house an air temperature sensor in a radiation shield to prevent radiation loading on the sensors; a side effect is that the air temperature entering a shield is modified by interior solar radiation, infrared radiation, airspeed, and heat conduction to or from the sensor so that the shield forms its own interior microclimate."

Solar radiation increased temperature readings most for Gill, less for MMTS and CRS, and least for ASOS. Readings increased with solar elevation.

Infrared radiation (from the surroundings) increased temperature readings by day (not by night) most for ASOS, less for Gill, less for MMTS, and less for CRS.

Low wind speeds troubled all the non-aspirated screens. "...it was impossible to reach the accuracy claimed by manufacturers" when wind speed was less than 8 to 10 knots.


I could be wrong, but I reason that, if you need a Gentle Breeze to stop the screens over-heating, some holes drilled in the floor will do little good. They will definitely admit infrared radiation, which is a known problem.
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#126427 - 14/08/2005 23:08 Re: Stevenson Screen Design
Stephen-wx Offline
Weatherzone Addict

Registered: 15/07/2002
Posts: 1313
Loc: Oak Flats, Illawarra, NSW
I know people have a thing against artificially aspirated screens but if done correctly all you are going to do is keep a constant air flow that encourages the correct amount of circulation needed.

I'm only using a small motor and fan unit to aid the natural airflow not speed it up...

The way this is going to be done is with a small fan hooked up to a solar panel so that it only runs when there is increased radiation as the screen seems to read fine at night so far. Ideally I'd like to have setup for when there are low winds speeds but this would have to wait a bit for development hehe.

If the screen was in the middle of Death valley then we would need some crazy amount of forced aspiration.

I'll see how it turns out anyways and if I don't like it I can always rip the fan unit out. I just like being able to meddle with things hehe laugh laugh

On the subject of holes in the floor I'm pointing out that heat rises due to convection, The holes will aid circulation yes but to keep the temp reading correctly you would then in theory need a faster airflow in the screen to prevent heat up from this. I'd be very very reluctant to try this method.

The other prob you could induce is moist air rising from the soil if the screen is not far off the ground, for a purist the resulting readings probably would not be satisfactory.

Stephen
_________________________
Stephen Jarrett

my home AWS site: http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=INSWOAKF3


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#126428 - 15/08/2005 13:43 Re: Stevenson Screen Design
Stephen-wx Offline
Weatherzone Addict

Registered: 15/07/2002
Posts: 1313
Loc: Oak Flats, Illawarra, NSW
Well the fan unit is in and its doing it's job perfectly. The readings are close enough to my AWS to attribute any small variations to local factors ie 1. The AWS is in a large open space at the Airport and I am in a Gully.

The temps are alot more stable and are all reading the same as my other 2 manual thermometers.

Now the laughable part, all it took was the $13 solar education kit from Dick Smith, a hole was drilled in the base and the wiring run through a hole next to it. None of these holes are open so heat entering from below is not a worry.

The wiring runs up the bolts and out through the side of the lid which in turn is hooked up to the solar panel. Now whenever the sun shines the fan starts and sufficient air circulation is not a problem.

I'm one happy person to say the least laugh

Stephen
_________________________
Stephen Jarrett

my home AWS site: http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=INSWOAKF3


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#126429 - 15/08/2005 13:56 Re: Stevenson Screen Design
Rime Offline
Weatherzone Addict

Registered: 07/06/2001
Posts: 1443
Loc: Perth,WA
It maybe a point that there could be problems with having holes at the bottom of the screen, however, the BoM standard screens all have this. I have always placed holes on the bottom of my screens as it seems to be the standard in Australia. The argument is that without the holes the screen can become a water trap and therefore you may experience a cooling due to evaporation. Just a note though, the BoM screens all have holes drilled in the bottom, but they also have them drilled in the ceiling.

Some years ago I built a wooden screen and left out the holes. Sure enough it it did become a water trap after heavy rain.

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#126430 - 15/08/2005 14:36 Re: Stevenson Screen Design
Rocky Raccoon Offline
Weatherzone Addict

Registered: 07/02/2003
Posts: 2061
Loc: Redan, Victoria
I haven't got holes on the bottom of mine but the I do have a triple ceiling, the bottom ceiling is louvred and part of the screen box and air can flow through freely between upper ceilings and no sunlight can possibly get in.
Ventilation is excellent.
I think one problem with holes on the floors is not to have huge ones or birds may enter it easily and damage your instuments.
I have seen them trying to break into my letterbox.
_________________________
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Rainfall total for 2012: 654.7mm
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#126431 - 15/08/2005 16:10 Re: Stevenson Screen Design
Rime Offline
Weatherzone Addict

Registered: 07/06/2001
Posts: 1443
Loc: Perth,WA
Quote:
Originally posted by Rocky Raccoon:

I think one problem with holes on the floors is not to have huge ones or birds may enter it easily and damage your instuments.
I have seen them trying to break into my letterbox.
LOL. I have not had any problems with birds as I think the holes are still a little too small. But from time to time I have problems with frogs getting into the screen. When it happens I have to go through the screen and collect the frogs. I put them into a bucket and then dump them down in the nearby creek. I have found that little ones are okay, but when the big tree frogs get in, they make a mess.

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#126432 - 06/09/2005 11:51 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Giant Mixing Bowl Thermometer Screen (Gimiboths)

In April I made a thermometer screen based on the Logan Village flower-pot saucer screen, described here:
http://weather.overflow.net.au/station/stevenson.html

I described my version in the "Remote Sensor" thread on 26-04-2005, and expressed my concerns about the way it worked in this thread (Stevenson Screen Design) on 23-05-2005.

I was worried that the maximum and minimum daily readings were too extreme. The observed temperature range was higher than usual in this region of high temperature ranges, and the values were more extreme than both my own back porch readings and the Tamworth METAR readings. Although the METAR is 38 km SSE, the climate controls are similar.

I built a new screen made of Giant Mixing Bowls. The defects I fixed were too little air-flow, too much mass, and too much trapping of water.

I will describe the new Gimiboths here. Separately I will compare data from the two screens and the METAR, and discuss factors causing the differences.

Gimiboths description

The Gimiboths looks like the Logan Village screen and is much the same size. However each element is a simple inverted bowl. The eight bowls comprise a roof, a ceiling, five wall units, and a floor. The bowls are mounted above a plywood base-board by three threaded rods.
The clear space for the thermometer inside is 50 mm radius, but the radius of the contained airspace is 120 mm. The height from floor to ceiling being 208 mm, the volume is 9.4 litres.
The bowls are separated by spacers 32.5 mm long, making the gap between bowls at the edge 7 mm. This is over three times the gap in my earlier screen. The smooth curve must also allow easier airflow. There is no line of sight to the thermometer from outside.
This screen weighs only 1.4 kg compared to the earlier screen's 4 kg. The thickness of the material is 1.8 mm rather than 2.7 mm, and I used no filler.

Materials

8x Poly Industries K032 Giant Mixing Bowls
3x 5/16" threaded rods
1 m 16 mm electrical conduit
1 m 10 mm or 12 mm PVC tube
3x 5/16 dome nuts
6x 5/16 nuts
3x 5/16 flat washers
plywood for base
(plus mounting bracket materials)
250 mm aluminium cooking foil
1 litre Prepsol or Prepwash
Sandpaper
Aerosol 400 g cans Motospray paint:
1x "Fast Drying Flexi Prime" ("...suitable for use on ...polypropylene...Adhesion Promoter")
2x "Acrylic Gloss White" ("Automotive Acrylic Top Coat Lacquer")
1 m binding wire

Method

The bowls must be cut and drilled. I am sure there are modern tools using heat or lasers, but I used ordinary drills, a hole saw,a coping saw and sanding disc. The polypropylene misbehaves when worked: it melts and chips.
The bowls start off 270 mm in diameter and 110 mm deep. Trim the four little feet off with a knife. Put each bowl upside down on a table and mark a cutting line about 30 mm up, clear of the pouring spouts. Drill a hole near the line to enter the coping saw blade, and saw away the top of each bowl. If necessary, sand the edge even.
On the base of the bowl, find the centre mark where the bowl was spun. Use a compass to draw a circle 62 mm in radius and mark for three holes on the circle. They should be 108 mm apart. Drill small pilot holes at these points and (for five bowls only) at the centre point.
Using the centre point holes to guide the hole saw, cut 100 mm diameter holes in five of the bowls. Enlarge the other holes to accept the mounting rods.
The bowls are not made completely convex but the ones for the roof, ceiling and floor need to be, so as to shed water. I "improved" them by heating over an electric element and rubbing with a teflon spoon.

Mark the conduit at intervals of 33.3 mm and saw off 24 pieces. Allowing for the saw cuts, this will space the bowls 32.5 mm apart. Cut 24 pieces of PVC tube to the same length, as spacers between the threaded rods and the conduit.
I made a triangular base board of heavy plywood drilled to take the threaded rods. I mounted the base board on a metal bracket, ensuring that the plywood formed an insulating barrier.
Assembly on the threaded rods, in my case, was: two nuts, base board, conduit, floor, conduit, wall, conduit,...wall, conduit, ceiling, conduit, roof, dome nut.

Painting

The screen must be painted for three reasons: 1. polypropylene is unstable in the sun; 2. the bowls let too much light through; 3. the screen must be white to reject as much radiation as possible.
Polypropylene is cheap but very hard to paint. The products mentioned above will do the job. (Getting an auto repairer to do it is another option.)
Dismantle the screen and arrange a set of hooks to hang the parts on for painting.
For each part, wash, sand, prepsol, sand, and prepsol, handling with gloves only. Paint with many light coats. One can of lacquer is not enough to make an opaque cover.
Finally, polish with car polish.

Final assembly

During assembly, I made a support for an Oregon and an Ewig wireless thermometer from binding wire.
I also glued a piece of aluminium cooking foil under the roof, shiny side down.

Supply of bowls

The K032 Giant Mixing Bowls are made by Poly Industries in Sydney and marketed through IGA stores. Only some stores have them, usually in small numbers, and prices vary widely: anything over $3.00 is a rip-off. I can offer a spare set of ten at cost.
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#126433 - 13/09/2005 23:52 Re: Stevenson Screen Design
Paul (Stargazer) Offline
Weatherzone Addict

Registered: 16/05/2003
Posts: 1170
Loc: Salisbury North, SA
Quote:
Originally posted by Surly Bond:
In April I made a thermometer screen based on the Logan Village flower-pot saucer screen, described here:
http://weather.overflow.net.au/station/stevenson.html
I also used the same plans to build my screen ... I posted details in this thread on Weatherzone.
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#126434 - 08/06/2007 07:59 Re: Stevenson Screen Design
Citizen Bob Offline
Junior Member

Registered: 07/06/2007
Posts: 2
Loc: Houston
How about a temperature shield based on an aluminum foil externally wrapped PVC pipe lined internally with longitudinally split styrofoam pipe insulation and aspirated by a fan?

A 4" ID PVC pipe with a 2" ID insulation would accommodate small wireless sensors like the La Crosse TX7U.

Regarding the effectiveness of PVC pipes as screens,

http://www.geo.uni.lodz.pl/~icuc5/text/P_6_5.pdf

where the authors compare various unaspirated screens with the Stevenson Screen.

With forced air circulation and nearly perfect thermal and radiation shielding, this pipe system should out-perform the simple pipes in that article.

You can use a computer fan and adjustable AC to DC converter brick with a built-in voltage adjustment (WalMart has them) to set the fan speed. Use wire mesh fan filters on both ends to keep critters out. The rest of the design is up to your imagination.

For remote applications a battery-backed solar power supply would keep the fan running 24x7 which is essential for a cramped design like this.

For larger applications I see no reason in principle why this design can't be scaled up to the largest available components which are at least as large on the inside as Gill shields made out of dishes.

Comments, please.

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#126435 - 08/06/2007 13:24 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
That paper you link by Erell, Leal and Maldonado is very interesting, Citizen Bob:
http://www.geo.uni.lodz.pl/~icuc5/text/P_6_5.pdf

By trimming the url I find that the paper was presented at the Fifth International Conference on Urban Climate at Lodz (Trivia: it's pronounced "Wooj"!), Poland, Sept 2003:
http://www.geo.uni.lodz.pl/~icuc5/

A PhD student recommended the Israeli horizontal tube screens to me years ago, but I decided to go for a Gill type (my "Gimiboths"). My screen must be very similar to the authors' Type 13. For a high-radiation site (as I also have), Type 13 turns out to be the best approach to a Stevenson Screen of the 16 screens that the authors tested. Like all the others it over-reads maxima and under-reads minima, if the Stevenson screen is taken to be correct: maxima were 1.76 deg over; minima were 1.40 under.

I seem to be getting maxima about a degree over, and minima about a degree under, readings in the Stevenson Screen at Tamworth Airport METAR. That could be due to other factors: it is nearly 40 km away, and a much windier site.

I still think that ventilated thermometer screens, though they give a better estimate of true air temperature, do not relate well to published temperatures recorded at standard met stations.
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#126436 - 10/06/2007 03:00 Re: Stevenson Screen Design
Citizen Bob Offline
Junior Member

Registered: 07/06/2007
Posts: 2
Loc: Houston
Quote:
Originally posted by Surly Bond:
I seem to be getting maxima about a degree over, and minima about a degree under, readings in the Stevenson Screen at Tamworth Airport METAR. That could be due to other factors: it is nearly 40 km away, and a much windier site.
I still think that ventilated thermometer screens, though they give a better estimate of true air temperature, do not relate well to published temperatures recorded at standard met stations.
I do not believe you can use temperatures measured outside your microclimatic environment, which is the one next to your thermometer. I have 4 amateur stations nearby my house and they are all a couple degrees different from one another.

I just mounted my LC TX7U on the covered patio away from the sun. I do not have any shield - it's just hanging naked. It is currently recording as much as 5 degrees F higher than the average of those 4 stations, and about 3F higher than the nearest station which is about 1/2 mile away. Clearly the patio is heating up from the sun.

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#126437 - 10/06/2007 10:12 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Hi Bob

Each person has to think through what they want to get data on.

I, for example, want to compare the climate inside my house with the climate outside it. My figures on the outdoor climate must be plausible to people who know where I live. However, the fact that there are a lot of trees around the house, and I am on a narrow ridge about 5 metres high is part of my environment. Figures I get will reflect these facts,and will differ from those at a typical met site.

I think a lot of people, when they first unpack their met station thermometers, will hang them in some shady area (like your covered patio). This is unlikely to be the best location once you have a proper screen. I think the thermometer should be as far away from other objects as you can get it. This is generally not very far: the size of the block of land, and the cost of wires and trenching, or reliability of a radio link limit the options.

Your horizontal pipe screen is very like the ones used by my student friend. He used 4 inch PVC pipe lined with plumber's insulation surrounding a smaller PVC pipe. I found I would have to buy quite a lot of materials and throw a lot away. You need access to a builders scrap heap.

May I suggest the mesh screens should not be metallic? A metal mesh in sunshine on the "air-in" end of the screen would heat the thermometer rather efficiently I think.

Cheers.
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#126438 - 10/06/2007 11:47 Re: Stevenson Screen Design
ROM Offline
Meteorological Motor Mouth

Registered: 29/01/2007
Posts: 6627
Interesting reading this thread although I am not into accurate weather recording equipment but I think SB would agree with me here.
There are significant short term temperature peaks lasting only a couple of minutes when thermals move through an area.
Recording equipment will register these peaks as higher temperatures even though they may only cover a small area of say a few hundred metres across and are a couple or more degrees above the overall temperature at the time.
Anybody who has ridden in the back of a ute on a still summer's evening will have felt the quite big changes in air temperature every few hundred metres as the ute drives through these warmer and cooler patches of air.
A good strong breeze or wind would have the effect of better mixing of the airmass but even here, strong thermals, ie; significant increases in the temperature of the local air mass, are still very obvious.
Thermal air mass temperatures and the temperature changes that occur when they drift through would be one of a number of reasons for large differences in temperatures between adjoining sites

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#126439 - 10/06/2007 16:01 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
This almost calls for its own thread,ROM.

I don't know much, but I can make a few points.

Most thermometers I know have rather long time constants, more than a minute, I think. They may not pick up some of these phenomena.

The big lumps of warm and cool air that you feel in the evening probably do not occur in the heat of the day, when we record the maximum.
When convection is active, air from a hot spot is rapidly mixed with air that is cooler. When the evening inversion has formed, the air a few metres above the ground is degrees warmer than air on the ground. Then air from a hot spot has nowhere to go; it just sits there, waiting for you to drive through.
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#126440 - 10/06/2007 17:26 Re: Stevenson Screen Design
ROM Offline
Meteorological Motor Mouth

Registered: 29/01/2007
Posts: 6627
I wouldn't argue with your assessment and I think you are probably right SB.
I thought the above might possibly be an explanation for different temps between closely situated recorders.

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#126441 - 13/06/2007 14:09 Re: Stevenson Screen Design
Carl Smith Offline
Member

Registered: 21/12/2001
Posts: 1042
Loc: Gold Coast
Some of those interested in Stevenson screen design may be interested in an experiment by Anthony Watts underway in the US to determine the thermal qualities of paints used on Stevenson screens.

To quote Anthony:

Quote:
Since they mentioned paint, I thought Id share this experiment with everyone. You may recall that Im conducting an experiment measuring the differences in temperature imparted by different coatins on the Stevenson Screens. Early screens were specd to have whitewash. I made up a batch of whitewash based on a known historical formula and setup a test rig:


Here is one days worth of plotted data related to whitewash -vs- latex -vs-
bare wood I have three weeks of this logged data and they all look pretty
much the same. Russ Steele was kind enough to plot the data for me for a day, May 21st.


These are temps recorded in a 1/4" borehole in the center of the wood slat
along with air temperature from an aspirated stacked plate IR shield. The
datalogger I used is NIST calibrated, and the probes are NIST calibrated.
Error is 0.1 degree F or less, and they are quite linear.

I have made it available on
http://www.surfacestations.org/downloads/paint_test1.zip These are all comma
demilited text files, suitable for import into R or Excel. This is three weeks worth of data.

The columnar format is:
date, time, Air Temperature, Bare Wood Temp(control), Latex Paint Temp, Whitewash Temp all in degrees F

I have my three new Stevenson Screens in, so Im going to switch now from
wood borehole tests of the painted slats to actual air temperature tests in
three standard Stevenson screens. I expect the temperature differences to be
smaller, but still measureable.

I have aquired the exact formula for lime based whitewash and the exact
materials from a chemist at the National Lime Company. They are watching
closely too becuase whitewash appears to be a superior coating for buildings
to create energy savings for air conditioning.

Will advise when the new experiment is up and running, it will be live online.
Positioning a screen is important too - Anthony has also got the ball rolling a photographic survey of all the screens used in the US climate network:

Some examples of what he has found so far:

A screen above a wood chips over weedmat surface that was hot to walk on surrounded by an asphalt car park.


A site listed as 'rural' and 'light=0' that is in fact mounted on a metal pylon next to a caretakers shack and car park:

Here is where the site above was located before someone had the bright idea to move it:


Another interesting position:

- I wonder how often they burn off the trash there!

Here is another 'rural' one in an irrigated ploughed field used for growing crops:

- note the steps needed to read the instruments because the screen has been elevated to keep it above crop height!

And perhaps my favorite:

- one wonders what effects jet exhaust has on the daily max!

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#126442 - 13/06/2007 14:25 Re: Stevenson Screen Design
Rob G Offline
Member

Registered: 31/07/2003
Posts: 434
Loc: Pennant Hills NSW
An interesting experiment Carl. However, the temperature of the outside surface of a screen must be just one parameter that determines inside temperature. For example, I read that screens painted black inside read lower than screens painted white inside. On the other hand, under very still conditions, the inside temperature would approach the screen surface temperature, while in windy conditions, or forced ventilation the surface temperature may only have a minor effect.

I wonder how a highly polished reflective surface would compare to white paint?

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#126443 - 26/06/2007 13:50 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Related threads

By chance, this thread has become the survivor of the various threads about thermometer screens (or shields, or shelters). There is a 3-page thread, "Stevenson Screen" now on p.6 of this index:

http://forum.weatherzone.com.au/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=006158

The thread "Remote Sensor" (2 pages), now on p.35, is also mainly about screens:

http://forum.weatherzone.com.au/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=005694
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#126444 - 26/06/2007 20:45 Re: Stevenson Screen Design
Paul (Stargazer) Offline
Weatherzone Addict

Registered: 16/05/2003
Posts: 1170
Loc: Salisbury North, SA
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Weather Station
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#126445 - 04/08/2007 20:08 Re: Stevenson Screen Design
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
Calibration of my home-made Gill-type thermometer screen.

I now have 27 months of daily maximum and minimum readings from my "Gimiboths" thermometer screen to compare with readings from the Tamworth METAR.

As I have mentioned, the Tamworth site is 38 km to the SSE, and is a "blasted heath" (short grass, actually), while my site is on a low narrow ridge with trees and houses.

I made a scatter diagram including plots of maxima and of minima separately. To the eye, both maxima and minima plot pretty close to a straight line through (zero:zero) with a slope of one to one. Of the maxima, one of my readings is about 5 degrees off the line, but nearly all are within 2 degrees from it. Of the minima, two readings are about 7 degrees off the line, but nearly all are within 4 degrees from it.

The regression line relating my maxima to Tamworth maxima is:
y=1.015x+0.67
At the highest Tamworth maximum, 41 degrees, my reading would then be 42.3 degrees: up by only 1.3.
At the lowest Tamworth maximum, 7 degrees, my reading would then be 7.8 degrees: up by only 0.8.
For this regression, R squared is 0.98.

The regression line relating my minima to Tamworth minima is:
y=1.006x-0.37
At the highest Tamworth minimum, 28 degrees, my reading would then be 27.8 degrees: down by only 0.2.
At the lowest Tamworth minimum, minus 5 degrees, my reading would then be minus 5.4 degrees: down by only 0.4.
For this regression, R squared is 0.94.

The discrepancies are rather small. In the daytime my screen reads about a degree over Tamworth. That could be because the trees and houses prevent cooling by the wind. At night my readings are, on the average, practically the same as those at Tamworth. However, there is a lot of scatter, shown by the lower value of R squared.
I believe this is to be expected. The flow of air at night will differ greatly from place to place and time to time.

I am encouraged to think that my screen is a success. I am confident that my screen readings represent the temperature (and humidity) in the environment of my house.
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#876951 - 13/08/2010 12:32 Re: Stevenson Screen Design [Re: Surly Bond]
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
There is now a photo of the Gimiboths home-made Gill-type thermometer screen in the "Indoor Climate" thread here.
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#876969 - 13/08/2010 14:53 Re: Stevenson Screen Design [Re: Surly Bond]
SBT Offline
Meteorological Motor Mouth

Registered: 07/02/2007
Posts: 13519
Loc: Townsville Dry Tropics

UK Steve - This goes to explain a bit about climate extremes in Australia because of the size of the country.

Northern Australia subject to Monsoons and Cyclones seasons, Wide climatic range from wet to dry tropics - high humdity and tempratures. Houses built to dissapate heat rapidly. Insulated roofs and walls with airconditioning - Cooling only or raised off the ground to catch the cooler breezes. Entire side walls made up of louvers floor to ceiling. High roofs trap heat well above the occupants and various forms of venting for teh roof cavity.

Middle Australia Mild almost Mediterranean Climate. Insulated roofs and walls. Airconditioning is reverse cycle (Heating and cooling). Quite a bit of central heating.

Southern regions Bloody cold. Central heating - very little if any airconditioning. Tasmania thinks a day over 30C is a heat wave and requires moaning about at great length.

In WA it is common to have temprature maximums of 44C in the Pilbra and down the southern coast at Esperance 14C. A temprature diffrence of 30C in the one state.

Size comparissons:
Australia / Europe
Australia / UK
Australia / USA
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#876981 - 13/08/2010 16:36 Re: Stevenson Screen Design [Re: SBT]
Surly Bond Offline
Weatherzone Addict

Registered: 23/08/2003
Posts: 1889
Loc: Manilla, near Tamworth NSW
I feel sure that Sir Boab's post is in answer to this one.
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