On 29 Aug, 19:46, "Nick Gardner"
wrote:

I haven't made any allowances for the low angle of the sun when rising and
setting as I find this varies due to distant hills to the ENE which means
that the sunshine recorder doesn't turn on until 17 - 20 mins after sunrise
during the summer months.

During the winter this is less of a problem and the sunshine recorder can
switch on just 12 - 14 minutes after sunrise with very clear skies.

Yes, electronic sensors are definitely quicker to pick up those early
rays, certainly when compared to a Campbell-Stokes recorder (bless
'em) with a dew-fogged sphere and a dew-sodden card taking much longer
to scorch than a dry card would.

My sensor - exposed on a high mast above the house - has twice picked
up sunshine within 2 minutes of sunrise, but both occasions involved
reflected rays off a cloud layer stretching almost to the horizon.
Even with a completely clear horizon and clear skies in summer I find
10-12 minutes is about the earliest that can be expected, and 20
minutes more typical; with the solar elevation only around 1 degree 15
minutes after sunrise (only twice the solar diameter) anything more is
pushing detection methods based on sensors with plane surfaces to
their limit.

What has surprised me ever since I first installed the instrument (in
Jan 2001) how little it is affected by dewfall or even a moderate hoar
frost. Only a snowcover seems to defeat it completely - my C/S was
much more sensitive to the slightest optical empairment of the sphere.

--
Stephen Burt
Stratfield Mortimer, Berkshire