Humidity and measuring.

[ericmark]

The stream in the woodland I visit dries up every year and the owner was wondering how the humidity change was impacting on the woodland so he bought a cheap humidity meter an electronic unit really designed for measuring humidity and temperature in house. Some clearly erroneous readings of 0% were recorded and although to start with 75% was recorded it then went to 100% and seemed to stay there. It was in a old bird box to protect from direct rain.

I bought a weather station temperature, humidity, and pressure with a remote unit which also reads temperature and humidity and tested the remote at home in the green house and to begin with like the other unit seemed to work but then that also started to show 95% which is the maximum it will record all through the day. So moved from greenhouse to shed and still only reading was 95%. I then moved in doors and very slowly the readings did start to move now one day latter showing 60% and all seems fine but it took a good 12 hours to show the reduced humidity and humidity changes quicker than that a lag of one hour may be acceptable but 12 hours makes it rather useless as over night it will likely reach 100% and the units never seem to recover over the day to give a near true reading.

Against all measurements my weather station shows trend up, static, or down and I would have thought if showing static then the unit had normalised to that environment however this from my experiments with just two units does not seem to be the case.

So ideas how can one measure humidity in the woodland? Is it down to old wet dry thermometer or is there some other way?

Because the temperature in the woodland varies I had used excel to show dew point and then back to show percent humidity at another temperature so I can truly compare moisture in the air. I wanted to see what the real difference was where the stream was running and where dry as air movement could still be taking moisture into dry stream areas. The stream dries because of sink holes in the lime stone and damming up stream has resulted in more water going through sink holes and so wanted to see if any correction was needed i.e. fill in some sink holes.

Personally I know very little about woodland management but as an engineer I was trying to help with measurement but clearly I have failed. Any ideas or personal experience into measuring humidity?

[oldclaypaws]

If it rains and everything looks wet, its humid.

If it doesnt rain for a while and it all looks dry, its not.

If you look up and see boats and fish going over the top of you, its very very humid.

If a Camel walks past looking for water, its very very dry.

[Dexter's Shed]

although I do have a proper weather station yet to fit in place in our woods, the one gives you the same information

[oldclaypaws]

I would never be without my 'Merryweather Tempest Prognosticator', which I take everywhere with me. It is of course, hopelessly inaccurate, and quite uncomfortable both to carry and when a leech escapes and latches on to your ear. Its forecasting accuracy is around 4%, so slightly better than the Met Office. A true work of Art, which as defined in the words of Mr Wilde, "is quite useless", but terribly British in conception and a worthy star piece in the 1851 Great Exhibition.

For anyone else wanting one, the modus operandi is detailed thus;

http://en.wikipedia.org/wiki/Tempest_prognosticator

[ericmark]

It would seem four types the electronic, the hair moving dial, and wet dry thermometer and the leach type. The wet dry needs a lot of calculations to work it out so not keen on them. So the other two would seem the better option. There are cheap ones that are really for amphibian tanks at £4 will not break the bank but these could fail in same way as electronic type. Had looked at data logging but again only any good if they work. I thought some one would have already tried using them so would have some experience which they could share.

[Rod Taylor]

Have used an 'Oregon scientific' (BAR808HG) for some years now in the house. It is a wifi system with outdoor sensor giving outside temperature and humidity readings. The sensor is on the outside wall in free air but close enough to the eaves to prevent being rained on. There is a memory function that gives max/min readings for the previous 24 hours. Current reading is 73% with max/min of 88%/73%.
I have no way of confirming the accuracy of these readings but they certainly change faster than the model you have described. The internal humidity reading certainly seems to change quite quickly and drops steadily after lighting the woodburner as it is in the same room, but not sure if it is safe to assume the same detector unit is fitted to both the indoor and outdoor unit.
Not previously considered taking this to the wood to take readings but wouldn't be a problem to mount the sensor protected from direct rain and the display unit close by in a waterproof container to see what results it gives over 24 hours, or carry the internal unit and see how long it takes for the readings to stabilise and assume it is a true reading. (Outside humidity just gone to 74% while typing this)
Hope this is of some help.

[ericmark]

Thank you so much for that. It does seem to be a combination of location and excess humidity which is causing my measuring problem. I considered in the shed was good enough clearly there would be a delay between outside conditions changing and changing in the shed but although the temperature has been floating up and down as expected the humidity outside seems to work OK when first taken out then once it hits 95% it stays there.

I suspect what every is doing the measurement is getting water logged as bring it inside again for few hours and it starts to read same as inside sensor then take outside again and works OK until it reaches 95% once that happens it sticks there again.

I think moving outside may improve things in that the air moves more and will dry it out but in the woodland the same problem as in the shed seems likely to return with not enough air movement. Even if I use a wet dry thermometer air movement will affect the readings the more air movement the drier it will record but at least it will not get water logged. However it will mean having to go out to read and converting readings into % humidity from tables.

Next is to talk about with problems in reading is it really worth all the work? We had considered using a data logger type but clearly they will suffer same fate as with radio link ones so pointless. Without before and after measurements we will not really know any meaningful results as to if our efforts are improving things or not.

What is going through my mind is home made one. Using a fir cone these are designed by nature to work in the woodland so connected to a dial so we can compare readings may work OK. Even better if it can be connected to a variable resistor and read indoors. So that seems a good project.

[Dexter's Shed]

we will not really know any meaningful results as to if our efforts are improving things or not.

What is going through my mind is home made one. Using a fir cone these are designed by nature to work in the woodland so connected to a dial so we can compare readings may work OK..

(so does my rock)

this is intriguing, how will any work you do, change the weather

[ericmark]

The consideration was to fill in sink holes or by-pass sink holes to keep the stream running throughout the year. Due to work up-stream the stream at the moment dies up in lower reaches. So will not change the weather but would change humidity as to if this is bad or good is another thing but since before the work above the woodland the stream ran whole length for most of the year I think likely good to return it to as it was.

[oldclaypaws]

I've twigged there are a couple of very good reasons why I'd like to do a simple experiment to determine the drier and wetter parts of my wood, and I can suggest a simple practical measuring technique. It might have an obvious and important application to many of us.

I suspect the variables which determine humidity/dampness based on my observations of logs and my freshly made pots are temperature, ventilation and overhead cover. These depend partly on the weather and seasons but equally location.

This is very important when is comes to choosing the best location for your log heap! I notice surprisingly, my logs at home in the open are quite dry (sunny/exposed). The ones in the open parking area at the wood are saturated (shaded/exposed). The ones under the trees in the wood are very dry at the moment. (shaded/under tree cover ).

Where I ask, is the driest place to stack my spare logs, and how to measure it? The answer I think is to use a standard piece of 'test timber' and a log moisture meter. If I cut several bits of 4"x2" pine to about 6" high (they are easier to find again than natural logs and will be uniform), I can dot them in several locations. Its then just a matter of sticking the log meter against them and reading off how dry they are. Obviously after rain the ones in the open will be wet, but certain locations will be drier for more time, and these presumably (if access is OK) might be the better places to leave logs.

It could also be useful if considering air drying cut timber, you don't want valuable timber left where it might be damper to decay. .... And you might not want to 'glamp', or have your hut or campfire in the dampest hollow in the wood. I shall try my 4 x 2 experiment and see if there's a simple formula to drier places. Gosh, does that make me a scientist?