On Sunday, 22 April 2018 17:00:00 UTC+1, Nick Gardner wrote:
On 22/04/2018 12:45, Keith Harris wrote:
I'm closely comparing my InstroMet and Blake-Larsen sun recorders, especially through this period of long days of sunshine, both of which work in different ways.

Keith, I am finding that the BL under-records by about 15%. It seems to
have difficulty registering sunshine if conditions are slightly hazy as
the thresholds appears to be set too high even though there are
well-defined shadows. I have contacted Ole about this but he seems to
think the recorder is working fine.

A classic example was the other day when there were thin contrails and
these were enough to cause the reading to drop below the threshold even
though the sun was still shining strongly with very distinct shadows.

My R&D recorder, like yours turns on about 40 minutes or so before the
BL at dawn. At dusk the BL turns off about 20 minutes before the R&D.
The only way the two recorders nearly record the same is when the sky is
exceptionally pristine with no haze at all, i.e., extremely deep blue
all the way down to the horizon - and that doesn't happen that often.

Here are my sunshine data for the last few days noting that the skies
were cloudless on the 18th, 19th & 20th:
R&D BL
18th 13.1 11.3
19th 13.2 11.6
20th 13.1 10.9
21st 7.4 5.4

Another issue that I have with the BL recorder is that it is totally
reliant on the program running all the time. There have been occasions
when the program crashes and doesn't restart. All the data during the
downtime does not get recorded. It really could do with a data logger
and until it does I don't see it as being a serious contender to the
present sunshine recorder line-up.

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

Hi Nick,

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, but may conflict with what the human eye regards as full sunshine and is basing it's functionality on solar radiation, not shadow. I'm sure Ole won't mind me quoting his reply as I think it sums up our delemma:

snip
The human interpretation of what sun shine is to a certain extent is also quite subjective – how deep is the shadow casted before we deemed is as sun shine?

I have discussed the WMO definition of 120W/m2, which is very old and also to a great extent on the Cambell-Stoke performance.

When observing a very nice clear sun rise, our human mind surely says – yes – sun is shining, but the 120W/m2 is never reached just after sun rise but at something like 5-7° above the horizon (as far as I remember).

So the big issue is if sun shine is based on the light or on the radiation.
snip

I know what you mean with regards if the programme crashes, mine has been quite reliable lately, it does still record if the internet goes down, but of cours you won't see the 1/2 hourly updates online. The *new* SMS and email 'alarms' and daily & weekly summaries are good. Of course the only time you can do any maintanance with the software is out of sun day hours.

Some Months ago I also got the data logger for my R&D InstroMet sun recorder, but the data logged does not agree with the data on the display, it is always a lot less. Adrian was going to look at this using an old device, but as yet not had an answer nor a solution.

Eg:
Today Display 11:25, logger output 11:15.
18th Display 13:42, logger output 13:25.

Regards

Keith (Southend)