That's not problematic, the 127mm (5") properly exposed, would be tge accepted rainfall.

On 2014-01-25 15:37:46 +0000, Vidcapper said:

On 25/01/2014 11:06, Norman wrote:
Vidcapper wrote:

Would the mounting poll being slightly off-vertical (presumably knocked that
way by the recent strong winds) adversely affect recorded totals?

Presumably the buckets would each tip with different amounts of water, but
wouldn't they offset each other?


I don't know how much difference it might make. In general, though, the Davis
VP raingauges seem to under-read compared to a standard 5-inch manual gauge.
Mine under-reads by 15-20%. It's the most disappointing feature of the Davis
VP. Undoubtedly, one of the reasons is that it is usually located some distance
above the ground whereas the standard 5-inch gauge is usually at ground level.


IRO rain gauge heights, I've found this interesting, if old, article :

http://www.hydrologynz.org.nz/downlo...v9_2_Green.pdf


I have the same problem with my VP, and after several 'experiments'
last summer, I concluded that the reed switch was not always activating
as the buckets tipped from one to the other, or if it was it was not
generating enough instant voltage to increment the counter at the base
station. This seemed to be more prevalent on one side of the bucket set
up to the other, but it was difficult to be certain.

If I counted the tips and then compared that with the display, I
always counted a higher figure; but even the display varied from one
experiment to the next. If I poured in enough water for 10 tips, quite
often the display total would be 8, but there were a number of times
when it was as low as 6.

I had intended to replace the reed switch, to see if that might help;
but I did not trust my quasi-accurate soldering ability, so at the
moment I have left it as it is.

"yttiw" wrote in message news:2014013010055416658-cuddles@britpostcom...

If I poured in enough water for 10 tips, quite
often the display total would be 8, but there were a number of times
when it was as low as 6.
===================

Let's hope that by 'poured' you mean dripped. If you did indeed just empty a
given volume of water into the funnel then it's not impossible that
individual tips might be missed (because of the unrealistically high
rainfall rate that would be simulated and which the gauge is not designed to
cope with). That's not to say that the reed switch might not be getting old
and less reliable and so also contributing to the apparent under-recording,
but it's essential to test correctly. And something around 100 tips-worth as
a total volume to drip through is recommended for a good test.

John Dann
www.weatherstations.co.uk

100 tips? Recommended by whom? The problem with all tbr systems is that they need to be calibrated regularly and most importantly, at installation. It's all very well a company saying that their system is accurate to whatever when it's produced but after it leaves the factory it's then subjected to being thrown about in transit etc, etc, which can alter the calibration. Calibration needs to be done correctly with a very accurately measured volume of water otherwise it's pot luck. Done properly, this doesn't require 100 tips. If you can get to within +/- 5% of a 5" then you're doing well. AWSs are great but most are probably inaccurate because they are rarely re-calibrated regularly if at all. This goes for temperature as well as rainfall.

On 2014-01-25 15:37:46 +0000, Vidcapper said:

On 25/01/2014 11:06, Norman wrote:
Vidcapper wrote:

Would the mounting poll being slightly off-vertical (presumably knocked that
way by the recent strong winds) adversely affect recorded totals?

Presumably the buckets would each tip with different amounts of water, but
wouldn't they offset each other?


I don't know how much difference it might make. In general, though, the Davis
VP raingauges seem to under-read compared to a standard 5-inch manual gauge.
Mine under-reads by 15-20%. It's the most disappointing feature of the Davis
VP. Undoubtedly, one of the reasons is that it is usually located some distance
above the ground whereas the standard 5-inch gauge is usually at ground level.


IRO rain gauge heights, I've found this interesting, if old, article :

http://www.hydrologynz.org.nz/downlo...v9_2_Green.pdf


I attempted some experiments last summer with my VP gauge, and my
conclusions were that the reed switch was not registering every tip for
some reason. Whether it was such a short voltage spike I do not know,
but checking the base station total after 10 tips of the gauge, I had
readings of mainly 6 to 8, one of 9 - but never the full 10.

I had intended to replace the reed switch, but without a knowledge of
electronics, plus an untrustworthy soldering technique I was worried
that I would do more harm than good.

On 2014-01-30 10:16:48 +0000, General said:

"yttiw" wrote in message news:2014013010055416658-cuddles@britpostcom...

If I poured in enough water for 10 tips, quite
often the display total would be 8, but there were a number of times
when it was as low as 6.
===================

Let's hope that by 'poured' you mean dripped. If you did indeed just
empty a given volume of water into the funnel then it's not impossible
that individual tips might be missed (because of the unrealistically
high rainfall rate that would be simulated and which the gauge is not
designed to cope with). That's not to say that the reed switch might
not be getting old and less reliable and so also contributing to the
apparent under-recording, but it's essential to test correctly. And
something around 100 tips-worth as a total volume to drip through is
recommended for a good test.

John Dann
www.weatherstations.co.uk

Thanks for that advice John. I did try and add the water at various
rates in order to simulate varying rainfall conditions, but I admit
that the 1-2mm an hour levels would be almost impossible to produce
manually.

Apologies for double posting, but some of my posts take so long to
appear, that I give up on them and try again. Very tiresome, I know,
and rather embarrassing.

If we ever get a dry spell, I will attempt the 100 tips test and see
how it goes.

On 25/01/2014 12:47, Vidcapper wrote:
On 25/01/2014 11:06, Norman wrote:
Vidcapper wrote:

Would the mounting poll being slightly off-vertical (presumably
knocked that
way by the recent strong winds) adversely affect recorded totals?

Presumably the buckets would each tip with different amounts of
water, but
wouldn't they offset each other?


I don't know how much difference it might make. In general, though,
the Davis
VP raingauges seem to under-read compared to a standard 5-inch manual
gauge.
Mine under-reads by 15-20%.

Mine started off under-reading by 10-15%, but recently that has risen to
about 30%.

I removed the funnel, and it didn't seem to be clogged up, and there
were no spiders lurking inside, so I'm not sure what's going on?

Following up, since I've re-aligned it back to vertical (or as close as
I can get it), the % under-reading compared to my standard copper rain
gauge for Feb to-date, is down to just 12%. In fact yesterday it
actually recorded *more* than the copper one!

--

Paul Hyett, Cheltenham