Solar Data

[ptb]

I didn't know whether to post this on Fine Offset page or this page, but in the end decided here - apologies if incorrect.

Whilst I realise there are many quirks with solar recording (such as accuracy, thresholds etc) can anyone enlighten me as to why the recorded data should differ greatly between C1 and CMX?
I’m presently moving from the former to the latter, and whilst my FO is connected to a PC running MX, once a day reconnect the logger to my old laptop and update my old C1 database. The data displayed ties up with the exception of "sunshine hours" - UV is OK.

Sunshine hours recorded from logger on C1 for 4th – 7th March are
1.0, 0.3, 2.0, 3.7
Yet same data source for the same dates viewed through CMX gives the following hours.
1.0, 0.7, 0.7, 2.0

(source dayfile.txt)
Have I got a setting wrong? I was hoping that I could continue keeping these records just for comparison rather than accuracy, yet I’m surprised that the raw data is interpreted so differently.
Any thoughts?

[Gyvate]

they (C1, CMX) probably use different algorithms.
Anyhow these algorithms usually try to get sunshine hours out of the intensity of the global solar (ir)radiation, which are never accurate; they are an estimate.
(even though I hear/read that a French meteorologist developed some formula/algorithm, also considering latitude and time of the year, which seems to be comparatively accurate).
Of course being happy with estimates is ok. I was not and got me a Larsen-Blake Sun Recorder which provides meticulous (minute, even second based data) of sunshine.
And CMX has an interface for the recorded sunshine by the B-L Sun Recorder.
You can look the result up on my main web site (see signature) near the bottom of the overview page.

[mcrossley]

Two thoughts, are your solar settings around sunshine exactly the same in C1 and MX?
What is your logging interval? MX will be calculating sunshine on a minute by minute basis, using the logger C1 will have a granularity of the logger interval.

[ptb]

Thanks both for your informative responses
As far as I can tell (i.e there are no obscure parameters to set other than in settings) they are the same.
Logging interval is 10 minutes so at the end of the day the C1 will be reading the logged data, whereas cmx will be reading the minute by minute data if I understand you correctly - I'm just now trying to get my head round the fact that a minute by minute log could produce more sunshine than the ten minute c1 log on one day but then less the next - I suppose it could just depending how fast the clouds were rolling by!!

[mcrossley]

So long as your latitude/longitude, and Station Settings > Solar are set the same, then C1 and MX should be using essentially the same calculation.

[ptb]

Ok thanks Mark. I’ll check that out.