I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem suspiciously
low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

Meanwhile the Met Office local forecast is showing around 80% which seems
quite high; I would expect it to be nearly turning misty if the air was
that saturated. Probably wrong of me, though.

I looked on Amazon (as you do) and there are some nice big gauges but the
reviews say they are accurate because they agree with the readings on
their digital thermometers.

Are these humidity levels reasonable?

If not, can someone recommend an accurate humidity meter which is not
horrendously expensive?

If I look up average humidity for March and get, for example:

https://www.currentresults.com/Weather/United-Kingdom/humidity-march.php

this again shows highs around 90 and lows around 70.

These are measurements of relative humidity (so water condenses out of the
air at 100%); is there a different measurement type?

All very puzzling as I would expect the weather to be reasonably heavy and
clammy at 90% humidity, although the same amount of water in the air at
10C outside and 20C inside would give quite a different relative humidity.

Whatever, the humidistat outside has still only got up to 33%. I shall
leave it for an hour and see what is changes to.

Cheers


Dave R


--
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On Saturday, 11 March 2017 13:52:09 UTC, David WE Roberts (Google) wrote:
I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem suspiciously
low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

Meanwhile the Met Office local forecast is showing around 80% which seems
quite high; I would expect it to be nearly turning misty if the air was
that saturated. Probably wrong of me, though.

I looked on Amazon (as you do) and there are some nice big gauges but the
reviews say they are accurate because they agree with the readings on
their digital thermometers.

Are these humidity levels reasonable?

If not, can someone recommend an accurate humidity meter which is not
horrendously expensive?

If I look up average humidity for March and get, for example:

https://www.currentresults.com/Weather/United-Kingdom/humidity-march.php

this again shows highs around 90 and lows around 70.

These are measurements of relative humidity (so water condenses out of the
air at 100%); is there a different measurement type?

All very puzzling as I would expect the weather to be reasonably heavy and
clammy at 90% humidity, although the same amount of water in the air at
10C outside and 20C inside would give quite a different relative humidity..

Whatever, the humidistat outside has still only got up to 33%. I shall
leave it for an hour and see what is changes to.

Cheers


There is only one accurate way to measure RELATIVE humidity.
Wet and dry bulb thermometers.
You can make one up yourself quite easily.
You will need a chart to covert the temperature readings to relative humidity.

https://en.wikipedia.org/wiki/Hygrom...thermometer.29

The chart:-
https://www.google.co.uk/search?q=ta...DnGcJBop_TU1M:

On Sat, 11 Mar 2017 13:52:06 +0000, David wrote:

I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem
suspiciously low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

Meanwhile the Met Office local forecast is showing around 80% which
seems quite high; I would expect it to be nearly turning misty if the
air was that saturated. Probably wrong of me, though.

I looked on Amazon (as you do) and there are some nice big gauges but
the reviews say they are accurate because they agree with the readings
on their digital thermometers.

Are these humidity levels reasonable?

If not, can someone recommend an accurate humidity meter which is not
horrendously expensive?

If I look up average humidity for March and get, for example:

https://www.currentresults.com/Weath...gdom/humidity-
march.php

this again shows highs around 90 and lows around 70.

These are measurements of relative humidity (so water condenses out of
the air at 100%); is there a different measurement type?

All very puzzling as I would expect the weather to be reasonably heavy
and clammy at 90% humidity, although the same amount of water in the air
at 10C outside and 20C inside would give quite a different relative
humidity.

Whatever, the humidistat outside has still only got up to 33%. I shall
leave it for an hour and see what is changes to.

Just brought it back in reading 58%.

Still nowhere near the 80-90% shown in the forecast.


Cheers


Dave R



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On 3/11/2017 5:05 PM, Chris Hogg wrote:
On Sat, 11 Mar 2017 08:08:46 -0800 (PST), harry
wrote:


There is only one accurate way to measure RELATIVE humidity.
Wet and dry bulb thermometers.
You can make one up yourself quite easily.
You will need a chart to covert the temperature readings to relative humidity.

https://en.wikipedia.org/wiki/Hygrom...thermometer.29

The chart:-
https://www.google.co.uk/search?q=ta...DnGcJBop_TU1M:


+1, just for a change. See also
https://en.wikipedia.org/wiki/Relative_humidity
Also, on Amazon, http://tinyurl.com/zjwbkwb http://tinyurl.com/jfacz8t
and http://tinyurl.com/jhbbqde


+ another 1

On 11/03/2017 13:52, David wrote:


All very puzzling as I would expect the weather to be reasonably heavy and
clammy at 90% humidity, although the same amount of water in the air at
10C outside and 20C inside would give quite a different relative humidity.


Therein lies the clue. The higher the air temperature, the more water it
can hold. At 10 degrees it can't hold very much - which is why even a
high relative humidity doesn't necessarily feel clammy. More likely to
feel 'raw'.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

David was thinking very hard :
I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem suspiciously
low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

Both values are unlikely. I have a weather station logging both values
contantly. 40 to 45 is normal indoors, outdoors will be around the 70
to 95% most of the time at this time of year. It tends to dip in really
cold weather, because the cold air cannot support much humidity.


Meanwhile the Met Office local forecast is showing around 80% which seems
quite high; I would expect it to be nearly turning misty if the air was
that saturated. Probably wrong of me, though.

On 11/03/17 18:56, Harry Bloomfield wrote:
David was thinking very hard :
I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem suspiciously
low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

Both values are unlikely. I have a weather station logging both values
contantly. 40 to 45 is normal indoors, outdoors will be around the 70 to
95% most of the time at this time of year. It tends to dip in really
cold weather, because the cold air cannot support much humidity.

It doesn't work like that.

What does tend to happen is that really cold weather freezes out the
moisture at night and when it warms up its temporarily low humidity.

Today humidity at my local RAF airfield (Lakenheath) has been around 88%
- since dark its 100%.

Inside if you take 100% saturated air at say 5C and heat it to 20C its
gonna be around 40% or less - roughly halves for every 10C

Winter internal humidity can be alarmingly low in frosty weather

Meanwhile the Met Office local forecast is showing around 80% which seems
quite high; I would expect it to be nearly turning misty if the air was
that saturated. Probably wrong of me, though.

No: mist forms at 100% by definition.



--
No Apple devices were knowingly used in the preparation of this post.

In article ,
David writes:
I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem suspiciously
low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

At 13:52 (the time of your post), it was 68.5%RH in East Finchley,
(and 17.8C). Don't know if you were anywhere near there at the time
you measured it.

Meanwhile the Met Office local forecast is showing around 80% which seems
quite high; I would expect it to be nearly turning misty if the air was
that saturated. Probably wrong of me, though.

Misty tends to be 100%, although 100% isn't always misty.
Actually it can go over 100% as air can be super-saturated, and this
forms mist on microscopic dust/polution particles, and condensation/dew
on surfaces, although again, 100% doesn't necessarily mean misty.

I looked on Amazon (as you do) and there are some nice big gauges but the
reviews say they are accurate because they agree with the readings on
their digital thermometers.

Are these humidity levels reasonable?

If not, can someone recommend an accurate humidity meter which is not
horrendously expensive?

If I look up average humidity for March and get, for example:

https://www.currentresults.com/Weather/United-Kingdom/humidity-march.php

this again shows highs around 90 and lows around 70.

These are measurements of relative humidity (so water condenses out of the
air at 100%); is there a different measurement type?

Yes, there's absolute humidity - this is specified as the temperature
at which, for a fixed quantity of moisture in the air, the relative
humidity is 100%. This is known as the dew point.

All very puzzling as I would expect the weather to be reasonably heavy and
clammy at 90% humidity, although the same amount of water in the air at
10C outside and 20C inside would give quite a different relative humidity.

Whatever, the humidistat outside has still only got up to 33%. I shall
leave it for an hour and see what is changes to.

Can be some lag. It's also important it is measuring the air temperature,
and not subject to significant radiative heating/cooling from the sun/sky,
or other objects which might be being heated by the sun or cooled by the
sky (look up a Stevenson Screen).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

That link is longer than most web pages by the sound of it.
How on earth do they manage to get such complexes addresses.
Brian

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This newsgroup posting comes to you directly from...
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"Chris Hogg" wrote in message
...
On Sat, 11 Mar 2017 08:08:46 -0800 (PST), harry
wrote:


There is only one accurate way to measure RELATIVE humidity.
Wet and dry bulb thermometers.
You can make one up yourself quite easily.
You will need a chart to covert the temperature readings to relative
humidity.

https://en.wikipedia.org/wiki/Hygrom...thermometer.29

The chart:-
https://www.google.co.uk/search?q=ta...DnGcJBop_TU1M:


+1, just for a change. See also
https://en.wikipedia.org/wiki/Relative_humidity
Also, on Amazon, http://tinyurl.com/zjwbkwb http://tinyurl.com/jfacz8t
and http://tinyurl.com/jhbbqde


--

Chris

On 12/03/17 10:06, Brian Gaff wrote:
That link is longer than most web pages by the sound of it.
How on earth do they manage to get such complexes addresses.
Brian

Its because he googled it and then cut and pasted what google used to
identify it which is tagged with lots of google private tracking info.



--
€œBut what a weak barrier is truth when it stands in the way of an
hypothesis!€�

Mary Wollstonecraft

On 12/03/17 10:24, Chris Hogg wrote:
On Sun, 12 Mar 2017 10:06:00 -0000, "Brian Gaff"
wrote:

That link is longer than most web pages by the sound of it.
How on earth do they manage to get such complexes addresses.
Brian

Harry doesn't seem to know how to use TinyURL.

Or google.


--
The biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.

On Sun, 12 Mar 2017 00:54:51 -0000 (UTC),
(Andrew Gabriel) wrote:

snip

Can be some lag. It's also important it is measuring the air temperature,
and not subject to significant radiative heating/cooling from the sun/sky,
or other objects which might be being heated by the sun or cooled by the
sky (look up a Stevenson Screen).

That takes me back ... we had a Stevenson Screen at primary school and
for a while I was one of those whose responsibility it was to log the
readings etc.

That was in the days when such things could sit outside and not get
vandalised or the equipment stolen from. ;-(

Now days though you can get something as cheap (10 quid), small and
low power consumption as a Raspberry Pi Zero W, install Linux and some
free software on it (Domoticz in this case) and have it regularly
scrape and log external weather stations (and other data sources, like
my cousins solar panels / battery) giving a whole wealth of mildly
interesting info. ;-)

This for example might be of interest to the OP:

http://i68.tinypic.com/24doimg.jpg

I have no idea how accurate it is but my wireless outdoor thermometer
seems to confirm the current temperature, +- a couple of degrees.

Cheers, T i m

p.s. This is the internal temperature log of the system when I changed
from a RPi3b to the Zero W. Assuming the internal temperature sensors
are accurate, it does seem to reflect how much lower power the Zero
would be over the Pi3.

http://i63.tinypic.com/2ic4kma.jpg

On 11 Mar 2017 17:20:59 GMT, David wrote:

Just brought it back in reading 58%.

Still nowhere near the 80-90% shown in the forecast.

Humidity varies greatly dependant on the local (very local)
enviroment. North side of a building will tend to have a higher
reading than the south side, if only due to the temperature
difference. Nearby vegetation, ponds, rivers and relative wind
direction will also affect it.

A centrally heated house at this time of year will be around 30% to
40%. If it's very close to, or below, 0 C outside for a day or three,
the inside humidity may drop to 25 %.

--
Cheers
Dave.

Dave Liquorice explained :
Humidity varies greatly dependant on the local (very local)
enviroment. North side of a building will tend to have a higher
reading than the south side, if only due to the temperature
difference. Nearby vegetation, ponds, rivers and relative wind
direction will also affect it.

A centrally heated house at this time of year will be around 30% to
40%. If it's very close to, or below, 0 C outside for a day or three,
the inside humidity may drop to 25 %.

This read a few minutes ago...

In 16.5C 48%
Out 10.7C 79%

Doors have been open, nice day, no heating needed, but it will go on
later. Outdoor sensors are near to rear end of back garden which is
still very wet.

Dave Liquorice formulated on Monday :
A centrally heated house at this time of year will be around 30% to
40%. If it's very close to, or below, 0 C outside for a day or three,
the inside humidity may drop to 25 %.

If the humidity drops very low indoors in winter, I tend to suffer from
dry lips etc. - then I add some humidity by placing trays of water on
the radiators.