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

"Richard Griffith" wrote in message
...
snip 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.


.... bought mine from Casella back in the 1970s (?1975 I think). Still
got it, still works fine - never any problems with breakage (if the
thermometers are held firmly in the 'cage' then there should not be);
problems to watch out for are of course getting into the routine of
reading the value quickly (and that gets difficult as you get older
and the eyes don't focus so well), shielding from the sun, choosing a
spot which represents where you are trying to measure data etc.

Also, I find, even after all these years, that the process of getting
the wick sleeve onto the wet bulb is fiendishly difficult! It's
annoying as the wick should be un-contaminated by dirt, grease etc.,
and handling via fingers isn't advised!

Otherwise - get one - makes you stand out from the crowd when you're
using the thing in the back garden - and is a great conversation
starter!

Martin.


--
Martin Rowley
E:
W: booty.org.uk

On May 23, 9:45*am, "Martin Rowley"
wrote:
"Richard Griffith" wrote in message

...
snip 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.

... bought mine from Casella back in the 1970s (?1975 I think). Still
got it, still works fine - never any problems with breakage (if the
thermometers are held firmly in the 'cage' then there should not be);
problems to watch out for are of course getting into the routine of
reading the value quickly (and that gets difficult as you get older
and the eyes don't focus so well), shielding from the sun, choosing a
spot which represents where you are trying to measure data etc.

Also, I find, even after all these years, that the process of getting
the wick sleeve onto the wet bulb is fiendishly difficult! It's
annoying as the wick should be un-contaminated by dirt, grease etc.,
and handling via fingers isn't advised!

Otherwise - get one - makes you stand out from the crowd when you're
using the thing in the back garden - and is a great conversation
starter!

Martin.

--
Martin Rowley
E:
W: booty.org.uk

Agreed, I never had any problems with durability and even though they
were often used by students at a secondary school, in all years and
sometimes out on fieldwork, I never actually had one break (though I
had one, or two pinched!!) I also had difficulties with the wicks -
same with wet and dry bulb thermometers - but maybe not as many
difficulties as martin recounts and water can sometimes spray out of
the reservoir, which always causes some hilarity! The same can't be
said about the durability of my Max and Min thermometers. My main
method of reconnecting the mercury was to flick the thermometer quite
hard, whilst holding on tight. Unsurprisingly, over the years, a
couple have slipped out of my grasp.......

Well done keeping the Rh slide rule, Richard! One should come with the
instrument anyway. I bought all mine from Casella too, but that was
going on 20 years ago now. I always foung them acurrate enough for my
purposes. They are good for microclimate studies around the garden/
School/town/football ground *))

Paul

Richard

It's worth noting that you should use distilled water in the reservoir.

I don't suppose it makes too much difference in the readings (although
my sling does say "for accurate readings, demineralised water must be
used"). However, using tap water leaves mineral deposits on the wick and
results in the wick breaking quite quickly.

Mine in a Casella too which I've used for over 20 years in the HVAC
industry.

Neil

Martin Rowley wrote:
"Richard Griffith" wrote in message
...
snip 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.


... bought mine from Casella back in the 1970s (?1975 I think). Still
got it, still works fine - never any problems with breakage (if the
thermometers are held firmly in the 'cage' then there should not be);
problems to watch out for are of course getting into the routine of
reading the value quickly (and that gets difficult as you get older
and the eyes don't focus so well), shielding from the sun, choosing a
spot which represents where you are trying to measure data etc.

Also, I find, even after all these years, that the process of getting
the wick sleeve onto the wet bulb is fiendishly difficult! It's
annoying as the wick should be un-contaminated by dirt, grease etc.,
and handling via fingers isn't advised!

Otherwise - get one - makes you stand out from the crowd when you're
using the thing in the back garden - and is a great conversation
starter!

Martin.

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

This thread does throw up an interesting question - What is the
recommended calibration procedure for temperature and RH sensors.

There are plenty of methods and procedures available for commercial and
pharmaceutical instruments but I've never looked into the standards for
calibrating meteorological instruments.

I presume they would be published and/or available from the MetO but a
quick look at the website revealed nothing.

Anyone got any insight on this??

Cheers
Neil

wrote:
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

On Fri, 23 May 2008 at 09:45:03, Martin Rowley
wrote in uk.sci.weather :

... bought mine from Casella back in the 1970s (?1975 I think). Still
got it, still works fine - never any problems with breakage (if the
thermometers are held firmly in the 'cage' then there should not be);
problems to watch out for are of course getting into the routine of
reading the value quickly (and that gets difficult as you get older
and the eyes don't focus so well), shielding from the sun, choosing a
spot which represents where you are trying to measure data etc.

Also, I find, even after all these years, that the process of getting
the wick sleeve onto the wet bulb is fiendishly difficult! It's
annoying as the wick should be un-contaminated by dirt, grease etc.,
and handling via fingers isn't advised!

ISTM that RH & DP are two of the hardest parameters to measure - even
two instruments side by side can record quite different readings.

*****

On a totally separate issue, I just bought myself a TN2 Infrared
Thermometer

http://www.thermometers4u.co.uk/details.cfm?prodID=38

Not because I intend to make serious use of it, but because I love
electronic gadgets (I bet I'm not alone in that here).

It's interesting to see the wide variation in surface temperatures over
very small distances, though.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Paul

Remember that the "sensing area" for laser infrared thermometers can be
quite large once the distance gets to a couple of metres or so.

People make the incorrect assumption that the temperature is read just
on the area of the laser spot. On my Fluke unit, which I use in my job
as a BMS controls engineer, the spot diameter is something like 30cm at
4m distance!

So trying to read say a pipeline temperature in a ceiling is pretty
pointless! I find mine most useful for checking chilled ceiling
operation where the chilled tiles are 4ft square and fairly uniform
temperature.

Cheers

Neil

Paul Hyett wrote:

*****

On a totally separate issue, I just bought myself a TN2 Infrared
Thermometer

http://www.thermometers4u.co.uk/details.cfm?prodID=38

Not because I intend to make serious use of it, but because I love
electronic gadgets (I bet I'm not alone in that here).

It's interesting to see the wide variation in surface temperatures over
very small distances, though.

On Sat, 24 May 2008 at 08:06:57, Neil wrote in
uk.sci.weather :

*****
On a totally separate issue, I just bought myself a TN2 Infrared
Thermometer
http://www.thermometers4u.co.uk/details.cfm?prodID=38
Not because I intend to make serious use of it, but because I love
electronic gadgets (I bet I'm not alone in that here).
It's interesting to see the wide variation in surface temperatures
over very small distances, though.

Paul

Remember that the "sensing area" for laser infrared thermometers can be
quite large once the distance gets to a couple of metres or so.

People make the incorrect assumption that the temperature is read just
on the area of the laser spot.

So what is the laser spot for, then?
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

On 23 May, 21:09, Neil wrote:
This thread does throw up an interesting question - What is the
recommended calibration procedure for temperature and RH sensors.

There are plenty of methods and procedures available for commercial and
pharmaceutical instruments but I've never looked into the standards for
calibrating meteorological instruments.

I presume they would be published and/or available from the MetO but a
quick look at the website revealed nothing.

Anyone got any insight on this??

To be technically correct, formal temperature calibration would
involve a true calibration check against known standards at a variety
of spot temperatures. This is rarely feasible or affordable for the
majority of amateur-run sites, not least because losing the
instruments for 3-4 weeks while they were off being calibrated would
likely leave a gap in records.

However, the next-best method is to use a travelling reference
instrument as a benchmark i.e. one which has been calibrated under
laboratory conditions. If your instruments are in a Stevenson Screen
or similar, it's easy enough to expose the travelling standard
alongside existing sensors and compare the readings over a period of
time (and ideally a wide range of temperatures). If the instruments
are not in a screen it's a little more troublesome getting the two
sensors close enough together to be reasonably sure they are measuring
the same thing. Best to compare under cloudy, breezy, dry conditions,
best of all at night and when the temperature is changing only slowly
(otherwise differential thermal inertia will skew results).

I've used such a method with a calibrated TinyTag logging
thermohygrometer (http://www.geminidataloggers.com/data-loggers/
tinytag-hand-held) over the last six months, and after even just a few
days of logged data it's surprisingly easy to pin down an accurate
calibration against existing instruments (both logged sensors and
mercury-in-glass thermometry). I found that the manufacturer's
calibration on my expensive Vaisala temp/RH sensor had drifted by 0.4
degC in 18 months. After 4 months comparisons using the new
calibration coefficients the mean error was 0.05 degC under all
conditions, and at night under slow rates of temp change the adjusted
calibration of the Vaisala sensor was within 0.2 degC of the benchmark
99.4% of the time. That's good enough for me!

The logger I used is quite expensive, and calibration is another £60
or so, but it's proved an easy and accurate method of checking the
calibration of my sensors. Sending it back to Gemini for recalibration
every couple of years isn't too expensive either, and of course does
not lose the record from the 'primary' sensor. A repeat of the cross-
calibration every 2-3 years should be sufficient for all but the most
exacting of meteorological purposes.

I will be writing up the method for COL soon, with more detailed
instructions and a template spreadsheet to generate calibration
coefficients. I hope to persuade COL to buy a few of these calibrated
loggers for loan to members, which will make the whole process cheaper
and easy to carry out.

I also had my thermohygrometer humidity sensor calibrated, but I have
to say I've been less impressed with the accuracy of this RH sensor
and its calibration than I have with the temperature sensor. Not a
particular problem, as temperature was the element I was seeking a
calibration method for, but RH is altogether more difficult to pin
down to within 3-5 per cent at best, despite the claims of the
manufacturers.

I can highly recommend the TinyTag logger range btw: I have since
bought another smaller temperature logger without a display but with a
trailing thermistor on a 600 mm lead (ideal for comparing inside, say,
a Davis AWS screen, which is where mine currently is). They are about
half the price of the logging thermohygrometer with display. I
previously compared the new unit against my existing calibrated
standard over 2-3 weeks and 'out of the box' the mean error was
0.05 degC and 98% of readings were within 0.2 degC of the calibrated
unit. You can also buy these smaller units with calibration
certificates as new and they can be recalibrated for a relatively
small charge as and when required. Don't buy the small 'self-
contained' temp logging units though, at least not for accurate
meteorological purposes, as their response time is slow (~ 20 minutes
is quoted, vs 10 sec for the trailing thermistor sensor).

HTH.

--
Stephen Burt
Stratfield Mortimer, Berkshire