"Nick Gardner" wrote in message
news
"Bernard Burton"
I don't think that the KZ rcorder uses the same method as the R&D, Nick.
The
latter uses a shadow post to generate a difference in output from a ring
of
photo-diodes. The KZ uses '3 photo-diodes with specially designed
diffusers
the determine when a threshold of 120 W per sq m is exceeded'
See also:
measuringtheweather.com/wp-content/uploads/2012/06/An-overview-of-sunshine-recorders-July-2012.pdf
by Stephen Burt.
Bernard Burton

Bernard, I've just read the link to Stephen B's article and he
says that the KZ works by having at least one of the three
photodiodes in the shade giving a voltage differential. This is a
similar principle to the R&D.

Stephen also writes in the book version of Measuring the Weather
that the KZ and the R&D are likely to give close results as they
use similar principles to determine whether the sun is shining or
not.

The BL uses a simple solar irradiation measurement coupled with a
quite clever software code to determine a sunshine/no sunshine
output.

--
Otter Valley, Devon
20 m AMSL
http://www.ottervalleyweather.me.uk

I was quoting from the KZ litrature Nick, unless thay have changed the
design since that was written, I would accept what they say.
--
Bernard Burton

Satellite images and weather data for Wokingham at:
www.woksat.info/wwp.html



---
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On 23/04/2018 12:43, Keith Harris wrote:
So it is true what Ole said, and the algarithm seems correct based on
the WMO definition of 120W/m2, which is very old...

I'm not sure that the age of the definition has much to do with it (is
it very old anyway?). Isn't the reality that sunshine hours is not
actually a well-defined parameter and can't be because what you're
trying to measure, ie the boundary between bright sun conditions and
not, is subjective. It's a different kind of parameter to eg temperature
or rainfall. So different measurement techniques inevitably give
different answers and probably always will.

The WMO definition is one approach and an appealing one because it
defines a threshold which can be accurately measured with the right kit.
But how well it parallels human feelings about what is bright sun,
especially in hazy or dawn/dusk conditions, is endlessly debatable.

I suppose an alternative definition could be built around just how sharp
a shadow might be, given modern sensors and image analysis software. But
even so, someone will still need to make the call about precisely where
the cutoff is to be made.

On 22/04/2018 20:28, Graham Easterling wrote:
OK, there are a few assumptions, but all this suggests that the BLake Larsen is under-recording slightly (compared to Camborne) by perhaps 5%, but certainly a fair bit less than the 15% that Nick is experiencing.

Graham, Ole has just contacted me and has recalibrated the threshold as
it was set too high. That probably explains the rather large
discrepancy. Also, I have noted that the sensor is catching a shadow
caused by the apex of the dormer before sunset. The sensor is a little
below the R&D recorder which itself gets a clear view of the western
horizon. My mistake so I'll plan to get 'up there' and sort it at some
point in the near future.

Interesting that today the BL recorded 1.2 hours and the R&D recorded
1.1 hours. That's the first time the BL has recorded more so the
calibration seems to have worked!

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

On Monday, April 23, 2018 at 7:25:32 PM UTC+1, Nick Gardner wrote:
On 22/04/2018 20:28, Graham Easterling wrote:
OK, there are a few assumptions, but all this suggests that the BLake Larsen is under-recording slightly (compared to Camborne) by perhaps 5%, but certainly a fair bit less than the 15% that Nick is experiencing.

Graham, Ole has just contacted me and has recalibrated the threshold as
it was set too high. That probably explains the rather large
discrepancy. Also, I have noted that the sensor is catching a shadow
caused by the apex of the dormer before sunset. The sensor is a little
below the R&D recorder which itself gets a clear view of the western
horizon. My mistake so I'll plan to get 'up there' and sort it at some
point in the near future.

Interesting that today the BL recorded 1.2 hours and the R&D recorded
1.1 hours. That's the first time the BL has recorded more so the
calibration seems to have worked!

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

Glad you've found the probable issues Nick. I've obviously had no experience of using the Blake Larsen, but everything I'd read, and been told, suggested that over a month or 2 there was very little difference between it and the other recorders. Alan had also told me about successful parallel trials.. I thought there had to be a reason(s) why yours was 15% low.

I know that a firm has now taken over development of the Sun Recorder, so hopefully there will be some progress on the data logging front.

Graham
Penzance

On Monday, 23 April 2018 19:25:32 UTC+1, Nick Gardner wrote:
On 22/04/2018 20:28, Graham Easterling wrote:
OK, there are a few assumptions, but all this suggests that the BLake Larsen is under-recording slightly (compared to Camborne) by perhaps 5%, but certainly a fair bit less than the 15% that Nick is experiencing.

Graham, Ole has just contacted me and has recalibrated the threshold as
it was set too high. That probably explains the rather large
discrepancy. Also, I have noted that the sensor is catching a shadow
caused by the apex of the dormer before sunset. The sensor is a little
below the R&D recorder which itself gets a clear view of the western
horizon. My mistake so I'll plan to get 'up there' and sort it at some
point in the near future.

Interesting that today the BL recorded 1.2 hours and the R&D recorded
1.1 hours. That's the first time the BL has recorded more so the
calibration seems to have worked!

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

I generally find the R&D records more on clear days, mainly because the BL doesn't treat a hazy sunrise / sunset as full sun. However, with a very clear start today the BL started recording within 15 minutes of sunrise. But to my surprise the BL recorded 7.73 hours and the R&D only 4.77 hours, 3 hours less. So far the months totals are BL 117.06 hours, R&D 113.56 hours.

Keith (Southend)

On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote:
On 22/04/2018 18:30, Keith Harris wrote: I've come to the conclusion
you can't compare the two systems like for like. However, I do feel the
BL is more accurate,
Hmmmm, at the moment I am far from convinced that the BL recorder is
'more' accurate. I find it hard to believe that when the sun is shining
brightly and you can feel its heat, with its disk clearly visible and
there is a distinct, sharp edged shadow on the ground - that the sun is
NOT shining. The BL recorder can say that.

Also, and Ole agrees with me that the BL recorder can be fooled by
indirect light, i.e., lots of small cumulus clouds giving plenty of
reflected light can raise (as it does with my solar irradiation and UV
measurements) the level somewhat above the threshold and record sunlight
even though the sun itself is partly obscured and not casting a shadow.
I have noticed this on occasions and I contacted Ole to report it.

The Met Office might take some convincing as to the 'accuracy' of the BL
as I believe the KZ recorder uses the same method as the R&D, i.e., the
difference between sunlight and shadow.

I prefer to keep it simple, if there's a sharp-edged, distinct shadow
then then the sun is shining.

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

I've not noticed the indirect sunlight recording, however, today my R&D recorded 0.02 hours, whereas the BL 2.00 hours, it did brighten up, but I don't remember much blue sky. It's a shame I wasn't at home as I would like to have monitored what was going on.

Keith (Southend)

On Wednesday, April 25, 2018 at 6:39:48 AM UTC+12, Keith Harris wrote:
On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote:
On 22/04/2018 18:30, Keith Harris wrote: I've come to the conclusion
you can't compare the two systems like for like. However, I do feel the
BL is more accurate,
Hmmmm, at the moment I am far from convinced that the BL recorder is
'more' accurate. I find it hard to believe that when the sun is shining
brightly and you can feel its heat, with its disk clearly visible and
there is a distinct, sharp edged shadow on the ground - that the sun is
NOT shining. The BL recorder can say that.

Also, and Ole agrees with me that the BL recorder can be fooled by
indirect light, i.e., lots of small cumulus clouds giving plenty of
reflected light can raise (as it does with my solar irradiation and UV
measurements) the level somewhat above the threshold and record sunlight
even though the sun itself is partly obscured and not casting a shadow.
I have noticed this on occasions and I contacted Ole to report it.

The Met Office might take some convincing as to the 'accuracy' of the BL
as I believe the KZ recorder uses the same method as the R&D, i.e., the
difference between sunlight and shadow.

I prefer to keep it simple, if there's a sharp-edged, distinct shadow
then then the sun is shining.

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalleyweather.me.uk

I've not noticed the indirect sunlight recording, however, today my R&D recorded 0.02 hours, whereas the BL 2.00 hours, it did brighten up, but I don't remember much blue sky. It's a shame I wasn't at home as I would like to have monitored what was going on.

Keith (Southend)

My issue with any single fixed threshold is that it doesn't allow for seasonality - in higher latitudes at least, I don't regard winter's bright sunshine as being equivalent to summer's bright sunshine. But I agree with the notion that when compared with rainfall and temperature measurement, sunhisne measurement will always be more subjective.

On 25/04/2018 08:36, wrote:
On Wednesday, April 25, 2018 at 6:39:48 AM UTC+12, Keith Harris
wrote:
On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote:

The Met Office might take some convincing as to the 'accuracy' of
the BL as I believe the KZ recorder uses the same method as the
R&D, i.e., the difference between sunlight and shadow.

I prefer to keep it simple, if there's a sharp-edged, distinct
shadow then then the sun is shining.

I think that is a reasonable definition - otherwise thin cirrus haze
with the sun barely visible could be counted as sunshine. It is often
not far short of a similar brightness with ~90% transmission.

Cloudy bright in the old photographic rule of thumb era.

I've not noticed the indirect sunlight recording, however, today my
R&D recorded 0.02 hours, whereas the BL 2.00 hours, it did brighten
up, but I don't remember much blue sky. It's a shame I wasn't at
home as I would like to have monitored what was going on.

Keith (Southend)

My issue with any single fixed threshold is that it doesn't allow for
seasonality - in higher latitudes at least, I don't regard winter's
bright sunshine as being equivalent to summer's bright sunshine. But

That is more a flux per unit area on the ground.

Once the sun's altitude is more than about 15 degrees the extinction is
less than a magnitude. IOW 40% of the suns light reaches the ground. But
it is spread more thinly and for a shorter time in mid winter. See

http://www.orion-drustvo.si/MBKTeam/...extinction.htm

Interestingly with solar panels in mid winter the much cooler conditions
partly compensate for the low sun by improving PE efficiency.

I agree with the notion that when compared with rainfall and
temperature measurement, sunhisne measurement will always be more
subjective.

I always wanted one of the charred paper crystal ball sun recorders.

--
Regards,
Martin Brown

..

I always wanted one of the charred paper crystal ball sun recorders.


Here's one for sale

https://www.metcheck.co.uk/collectio...recorder-25-60

and don't forget the cards

https://www.metcheck.co.uk/collectio...recorder-cards

I notice one went for £750 on ebay this year.

On 25/04/2018 11:55, Metman2012 wrote:
.

I always wanted one of the charred paper crystal ball sun recorders.

Here's one for sale

https://www.metcheck.co.uk/collectio...recorder-25-60

and don't forget the cards

https://www.metcheck.co.uk/collectio...recorder-cards

I notice one went for £750 on ebay this year.

Ouch! That is expensive. I was planning on a DIY version using a 4"
glass ball I ordered up from China on eBay when I get a roundtuit.

Another slightly weather related demo I have always wanted to do is
start a fire from sunlight using a lens made out of clear water ice.
My attempt this winter failed as the hemispherical mould leaked.

--
Regards,
Martin Brown