"Hugh Newbury" wrote:

Martin, It occurs to me that maybe the answer might be to restrict
the outlet from the AWS to its tipping bucket. Small as it is,
possibly it's still too large to cope with a deluge. The weight of
the rain in the bowl would force the water out more quickly.
Certainly my experiments today seem to suggest this. I'll think
about it for a day or two.

.... as John suggested (elsewhere in the thread) I would be reluctant
to restrict the flow - it might (almost certainly will) lead to bigger
problems.

Indeed, I'd be reluctant to do anything to *physically* alter the
collector/gauge until I was absolutely sure that the difference wasn't
'genuine' in the sense that there isn't another (external) factor
accounting for the results.

Looking at your data, you get some very close figures when the rain is
'steady', but the difference multiplies alarmingly when the rain is
intense and accompanied by strong winds (which as others have stated
seems to have been a feature of this summer), which would steer me
towards an exposure problem, which the loss due to (attempted) rapid
cycling of the sample accentuates.

I know this is going to sound 'clunky', but you might want to consider
mounting a passive collector adjacent to the AWS gauge (i.e. same
height/not more than 30cm apart) - even a jam jar and a plastic funnel
would do, just to see if it collects roughly the same amount of rain
at that location. It's not ideal as one will interfere with the other
of course, but I would hope that the difference wouldn't be more than
10%; at the moment, during some of your events you are getting
differences of 30% or so.

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

Is there not a better way of measuring rainfall? Rather than a
mechanical device like a tipping bucket that interferes with what is
being measured, why not something comparitively non-intrusive? I'm
thinking of some kind of device like a laser maybe. Surely a tipping
bucket isn't the pinnacle of water measurement technology?

--
comp.john at googlemail dot com

comp.john wrote:
Is there not a better way of measuring rainfall? Rather than a
mechanical device like a tipping bucket that interferes with what is
being measured, why not something comparitively non-intrusive? I'm
thinking of some kind of device like a laser maybe. Surely a tipping
bucket isn't the pinnacle of water measurement technology?


Splendid idea! Tell it to Davis (AWS makers in the US of A). They're
still grappling with Micro$oft and have only just heard of USB connections!

Hugh

--

Hugh Newbury

www.evershot-weather.org

Martin Rowley wrote:

... as John suggested (elsewhere in the thread) I would be reluctant
to restrict the flow - it might (almost certainly will) lead to bigger
problems.

Indeed, I'd be reluctant to do anything to *physically* alter the
collector/gauge until I was absolutely sure that the difference wasn't
'genuine' in the sense that there isn't another (external) factor
accounting for the results.

I expect you're right: I actually wasn't going to do anything permanent,
using putty/chewinggum etc. But I think I will tinker in a detinkerable
way and see what happens.

Looking at your data, you get some very close figures when the rain is
'steady', but the difference multiplies alarmingly when the rain is
intense and accompanied by strong winds (which as others have stated
seems to have been a feature of this summer), which would steer me
towards an exposure problem, which the loss due to (attempted) rapid
cycling of the sample accentuates.

I know this is going to sound 'clunky', but you might want to consider
mounting a passive collector adjacent to the AWS gauge (i.e. same
height/not more than 30cm apart) - even a jam jar and a plastic funnel
would do, just to see if it collects roughly the same amount of rain
at that location. It's not ideal as one will interfere with the other
of course, but I would hope that the difference wouldn't be more than
10%; at the moment, during some of your events you are getting
differences of 30% or so.

That's a good idea. I have a large funnel and lots of jamjars/bottles.
I'll report back.

Hugh

--

Hugh Newbury

www.evershot-weather.org

Hugh Newbury wrote:

Splendid idea! Tell it to Davis (AWS makers in the US of A). They're
still grappling with Micro$oft and have only just heard of USB connections!

Hugh


$deiety, really

man this is so sad. If I could get a schematic of interface and
protocol, I might just be able to transform an ancient cd-rom reader
into a useful device!
--
comp.john at googlemail dot com

TBH I'm really not convinced that any amount of tinkering is going to
change things much. I'd be much more inclined to look at a way of
getting your VP2 rain gauge down on to the ground.

There are two ways of doing this with a VP2 gauge. One involves
separating rain gauge and shield, which can be done with a couple of
spare parts and a short extension lead.

The other is simply to use a separate standalone 7852 Davis gauge (ie
the old WMII one), which is still available and is plug compatible
with the VP2 gauge. This option costs more but is significantly
simpler to do.

John Dann
www.weatherstations.co.uk

John Dann wrote:
TBH I'm really not convinced that any amount of tinkering is going to
change things much. I'd be much more inclined to look at a way of
getting your VP2 rain gauge down on to the ground.

There are two ways of doing this with a VP2 gauge. One involves
separating rain gauge and shield, which can be done with a couple of
spare parts and a short extension lead.

The other is simply to use a separate standalone 7852 Davis gauge (ie
the old WMII one), which is still available and is plug compatible
with the VP2 gauge. This option costs more but is significantly
simpler to do.

I'll try one of these later, perhaps.

Hugh

--

Hugh Newbury

www.evershot-weather.org

.... this might be of interest:-

http://www.onerain.com/includes/pdf/...ageRecords.pdf

Martin.



--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

Martin Rowley wrote:
... this might be of interest:-

http://www.onerain.com/includes/pdf/...ageRecords.pdf


Martin, Indeed it is: fascinating! One has to wonder why the tipping
bucket has been thought worth keeping for so long ( a century or more?).

I have a dream ... An ordinary gauge like a std one and at std height,
but with an electronic weighing device, as in bathroom scales, under the
collecting part. The weight could be transmitted along with other data
by wire or wirelessly as with the Davis etc. At 24hr intervals it could
be emptied by hand or maybe automagically, and the device zeroed.
Simple, efficient, reliable, except of course for the trees growing up,
ground changes etc.

I think I'll patent the idea.

Meanwhile, back to the tipping bucket ...

Hugh

--

Hugh Newbury

www.evershot-weather.org

On Tue, 04 Aug 2009 08:34:55 +0100, Hugh Newbury
wrote:
One has to wonder why the tipping
bucket has been thought worth keeping for so long ( a century or more?).


There have been quite a number of other designs too of course, eg
syphon arrangements. I dare say someone could write a fairly extensive
history (and may well have done so already for all I know).

Most AWS systems will want a fully automatic - ie self-emptying -
gauge and that presumably is the biggest challenge. The fact that the
TBR (tipping bucket) design remains the commonest, at least among more
affordable gauges, does rather suggest that it has stood the test of
time as the most cost-effective and perhaps, for all its faults, least
inaccurate/unreliable option.

But I do think that you need to separate out the location of the gauge
from its measurement mechanism. A VP2 gauge positioned on the ground
would have the single biggest source of variability removed and I
think you might then be surprised at the improvement vs a standard
reference gauge.

John Dann
www.weatherstations.co.uk