On 23 May, 07:42, "Richard Griffith"
wrote:
I've always been interested in one of these instruments and I'm thinking of
getting one to check Temperature / Humidity readings. I operate an AWS and
know the sensors I have are high quality and reliable etc but its always
nice to have a back up and/or be able to verify the data. Also with this
type of instrument you get an instantaneous reading, (I still have my RH
Slide rule!) *I would be interested to know peoples experiences using a
Whirling Hygrometer. I've heard various stories/comments over the years
about the idea of 'slinging' 2 glass thermometers around your heard on a
wood/plastic frame can/does have its problems *(How sturdy are they against
breakage etc) but if they give you accurate data then it may be worth
getting one.

Best Wishes

Richard
Horsham AWS
West Sussex

Personally Richard - I'd stick with your TinyTag logger! I've had a
whirling psychrometer for many years and used to check my AWS
calibration against it (the two psychrometer thermometers both had
calibration certificates), but as has been mentioned already (i) the
things are very difficult to read quickly and accurately to 0.1 degC
even with good eyesight - and mine is not that hot these days and (ii)
the small, narrow bulbs, while good for fast response, do respond a
bit _too_ quickly to a nearby head reading them. So all in all I
reckoned I was lucky to get within 0.5 degC except by pure luck ...

Don't forget also that the humidity slide rule will give incorrect
readings unless you use the aspirated scale (on mine you have to
reverse the central scale) as the psychrometric constants are
different.

The best thing to check your sensors against is a clockwork Assmann
psychrometer, but there's precious few of these left in good nick and
of course getting replacement thermometers with good calibration is
more and more difficult. In light winds and sunshine the screen itself
will produce a significant 'error' (occasionally 1 degC over an
'aspirated' value in the free air). I use my two calibrated TinyTag
loggers for accurate calibration checks these days - much more
reliable (certainly within 0.2 degC) than a whirling psychrometer
IMHO ...

HTH.

--
Stephen Burt
Stratfield Mortimer, Berkshire