Free to a good home ...

For discussion of any observing equipment, from Stevenson Screens and manual instruments to electronic weather stations

Re: Free to a good home ...

Postby Graham Webster » 2012 Sep 04, 17:56

Dave Evans wrote:I would be interested to hear your comments on the plastic screen, Stephen. I had one supplied by the Met' Office two years ago; it works well enough as a screen but the interior is completely black and, at least to my eyes, it makes it very difficult to read the vertically mounted thermometers ( wet and dry bulb ) when the sun is shining to the south/south east.
The black interior. combined with glare from the sun seems to negate the contrast between the spirit column and the white background of the thermometer. At times I find the only way to read the thermometers relatively quickly and accurately is to hold a piece of white card behind the thermometer to provide a contrast.
I've no idea on the thinking behind making the screen interior black as the traditional white finish on the wooden screens has worked admirably for years.


Hello Dave. When I first got my plastic screen I did notice a difference in light levels inside the screen. On dull mornings especially in December I seen myself remove the max and min thermometers from the clips to read them and replace them again. The black louvres are designed to absorb stray light entering the screen.
Graham Webster
 
Posts: 9
Joined: 2012 Sep 04, 17:11
Location: Baintown, Fife. 125m asl. Firth of Forth, 3km to south-east. Hill, 205m asl 1km to NNW.

Re: Free to a good home ...

Postby Stephen Burt » 2012 Sep 09, 10:52

I bought my Metspec screen from UK Weathershop last summer (2011). I obtained quotes directly from Metspec and from UK Weathershop; both were similar but UKWS offer a 10% discount to RMetS members, so I bought it from them.

The screen was ordered on 28 July and arrived direct from Metspec on 22 September, so nearer 8 weeks delivery than the 6 weeks quoted at time of order, but there was no great urgency to my purchase. In any case I did run the Metspec screen alongside my existing large wooden Stevenson screen for 7 months to assess any significant differences prior to replacing the wooden screen, which I did on 1 April.

I ordered the screen, the bespoke stand and the interior thermometer fittings on the same order. (I still have max, min, dry and wet sheathed thermometers in the screen, read daily, although my 'station standard' readings come from two calibrated platinum resistance sensors located close to the dry bulb within the screen: these are logged to a Campbell Scientific CR1000 datalogger.) I did think of trying to adapt the old screen stand to fit, but frankly it was more trouble than it was worth, and I didn't want to risk the expensive new screen blowing off in a gale if it were not securely affixed. That happened to me once before, in the great gale of 2 January 1976, and it cost me two expensive thermometers, so I didn't want that to make that mistake again!

The total invoiced price was £846 + VAT, £1015 inc VAT. A lot of money, but unfortunately even wooden screens to the same spec are not much cheaper these days ...

I can honestly say I've been very pleased with the screen. It requires almost no maintenance of course - a wash every 3-4 months is ample. The annual summertime task of repairing any woodwork on the old screen (which was new in 1993), preparing the woodwork for painting and then repainting all or part of the screen with two or three coats of paint was always a 2-3 day chore, and I'm very glad to see the back of it.

I've washed the screen thoroughly several times, but have not had any problems with broken louvres. The only other report I've heard of broken louvres (other than vandalism or accidental damage) came from the British Antactic Survey, where they had a problem with some early prototypes: the plastic tended to become brittle at low temperatures (below -20 °C or so) and snap with any pressure, but Metspec changed the plastic formulation thereafter and I understand that the problem went away. I suspect that wouldn't be a problem for most locations within the UK, of course!

From my own experience, I'm happy to recommend the Metspec plastic screen. From my careful side-by-side comparisons (10 m apart) with the existing large Stevenson screen the differences were slight - the Metspec screen being lighter and less bulkier does tend to react slightly faster to changing temperatures than the larger wooden screen, but that's entirely to be expected from their relative thermal inertia. The Met Office have run their own comparison trials of course, and found few significant differences: the results were written up in IJC in 2007 (ref 1).

To me, and I suspect to many other COL members, the low-maintenance aspect is a huge plus. If you have a screen that is beginning to show its age, it might be worth biting the bullet and ordering a plastic Metspec model rather than a new wooden one - after all, you'll still need to repair/repaint a new wooden one every couple of years.

For those who are interested, there's a comprehensive section on screen types, including advantages and disdvantages (basic and home-built units as well as the Stevenson and Metspec screen) in my new book, The Weather Observer's Handbook.

SB

Reference
M. C. Perry, M. J. Prior and D. E. Parker (2007) An assessment of the suitability of a plastic thermometer screen for climatic data collection. Int. J. Climatol., 27, pp 267-276
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: Free to a good home ...

Postby Graham Webster » 2012 Sep 10, 13:13

My Metpsec screen is one of the originals built in 2001. I believe the modern screens (like the one you have Stephen) are the mk2 which have much stronger louvres. My louvres have broken off at the tips, the louvre itself is in one piece. I wash the screen with thick sponge wipes. I don't have an outside tap so I can't use a power washer.

Its a horrible job sanding down then repainting a wooden screen with undercoat then gloss, I did it several times before i got my hands on a plstic one...and I wouldn't go back to a wooden one. I

Maybe I should use the UK Weathershop to buy a new one.
Graham Webster
 
Posts: 9
Joined: 2012 Sep 04, 17:11
Location: Baintown, Fife. 125m asl. Firth of Forth, 3km to south-east. Hill, 205m asl 1km to NNW.

Previous

Return to Equipment



Who is online

Users browsing this forum: No registered users and 2 guests

cron