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Copper rain gauge.

PostPosted: 2015 Mar 26, 11:28
by Richard Hunt
Hope this is not a stupid question.

I'm about to purchase a copper rain gauge with a funnel diameter of 123mm (Metcheck CM1037), which is just short of 5 inch.
The gauge I have seen comes with an internal plastic measuring cup, but I would prefer the glass measure (CM1013) with finer 1mm increments.

The glass measure is calibrated for a standard 5" gauge, the question is could I use the glass measure in a 123mm gauge and still be (fairly) accurate?.


The gauge and measure in question is from Metcheck.

Re: Copper rain gauge.

PostPosted: 2015 Mar 27, 09:35
by Darren Rogers
I hate to say it and obviously I could be wrong - but I don't think that the MetCheck gauge is a 'Standard' one.

I would at least compare with what Russell scientific or Fairmount sell first - but expect a price of £250-300.

wouldn't want you to spend the £125 with Metcheck and it not be right.

Re: Copper rain gauge.

PostPosted: 2015 Mar 27, 11:15
by Richard Hunt
Cheers for the reply Darren.

I know the official standard are expensive, but as I also don't have official exposure either I thought this would be a good compromise.


Hmmmm food for thought.

Re: Copper rain gauge.

PostPosted: 2015 Mar 27, 15:39
by Len Wood
Richard Hunt wrote:Hope this is not a stupid question.

I'm about to purchase a copper rain gauge with a funnel diameter of 123mm (Metcheck CM1037), which is just short of 5 inch.
The gauge I have seen comes with an internal plastic measuring cup, but I would prefer the glass measure (CM1013) with finer 1mm increments.

The glass measure is calibrated for a standard 5" gauge, the question is could I use the glass measure in a 123mm gauge and still be (fairly) accurate?.


The gauge and measure in question is from Metcheck.


Hi Richard,
With a slightly smaller diameter rain gauge you will be collecting slightly less rain in comparison with a standard 5 inch gauge.
The question is, if you use a measuring cylinder for a 5 inch gauge what will the error be?

I have done some arithmetic, square of gauge diameter over square of cylinder diameter, and

For a 5 inch (127 mm) gauge, the factor is 1 in 17.92 .

In your case with a gauge of 123 mm,
the factor is 1 in 16.81 .

So the error is small, less than 6% under measurement.

The trouble is, if you sum daily measurements over a longer period of time, a month or year, the error would build up.

Re: Copper rain gauge.

PostPosted: 2015 Mar 28, 11:32
by Richard Hunt
Thanks Len for the maths, I did think that would be the case.

I'll have to rethink this, and may be spend a little more on a 5" gauge.

Thanks again for the detailed explanation though.

Re: Copper rain gauge.

PostPosted: 2015 Mar 29, 12:00
by Mike Brown
There have been a number of 5" copper gauges and measures on eBay recently at prices well under your budget. Really worth a look. I have obtained a couple of them myself and they have been completely functional. If you look at this one

http://www.ebay.co.uk/itm/Vintage-coppe ... 3cf4afc6f7

A Snowden gauge. Without measure for £50. Leaves you change to buy a measure.

Just a thought

Best wishes

Mike

Re: Copper rain gauge.

PostPosted: 2015 Mar 29, 12:45
by Richard Hunt
Thanks for the link, yes I have seen that, and have pondered second-hand.

I may go that route to be honest.

Thanks for the link.

Re: Copper rain gauge.

PostPosted: 2015 Apr 02, 17:23
by Stephen Burt
I wouldn't touch the Metcheck one with a bargepole. Looking at the photograph (model CM1037 - http://www.metcheck.co.uk/acatalog/CM1037.html) it's obvious that this is NOT a standard gauge.

The most obvious deficiencies are, in addition to the non-standard funnel diameter:

1. It has a shallow funnel; the deep funnel of a standard gauge is vital to avoid outsplash in heavy rain, and is much better at retaining hail and snow.
2. There is no narrow-necked inner bottle to collect the precipitation - only the plastic measure. As this has a wide neck, it will be much more likely to suffer from evaporation losses.
3. There's no inner can. If the plastic measure overflows, the rain would presumably be collected in the body of the gauge - but you'd have to dig it up to empty it.
4. It appears to have a brass rim, but difficult to be sure; a substantial and accurately-turned brass rim is essential to maintain the circular gauge aperture.

Standard copper gauges are pricey, but they last forever. I bought mine with the proceeds of a Saturday job as a teenager in 1975 and it'll last me for the rest of my life, without a doubt.

Mike Brown's ebay suggestion is a good one - and £50 is a good price; I'd snap that one up if it's still there!

SB

Re: Copper rain gauge.

PostPosted: 2015 Apr 02, 20:11
by greg_gruner
I use the CoCoRaHS plastic rain gauge (available from ProData - see http://www.weatherstations.co.uk/cocorahs.htm). While obviously not of the same quality as a traditional copper gauge, it did come out quite well in some trials that Stephen performed (http://measuringtheweather.com/equipment-reviews/), which is the reason I bought one. For me it performs well. At £45 from ProData it is cheaper than the Metcheck one.

Re: Copper rain gauge.

PostPosted: 2015 Apr 02, 21:28
by Stephen Burt
I would agree with Greg. In my opinion, the two alternatives are, depending upon budget, the CoCoRAHS gauge and a standard Snowdon or Mk II copper gauge. Both are far superior to taking the dubious calibration of AWS tipping-bucket gauges as gospel.

Of course, site and exposure factors must also be considered, and there is little point in splashing out £250 or so on a standard gauge if your site is the main limiting factor in obtaining accurate and reliable rainfall measurements ...

SB