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'[EE][PIC] best method to measure rain qty'
2008\06\29@164754 by Dario Greggio

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What would be the best method to measure quantity of fallen rain? (meteo
station)

A cup/glass and two resistive bars? possibly using AC instead of DC to
prevent oxidation? Or any other suggestion?
And, does it need to be emptied once in a while?

TIA everybody.

--
Ciao, Dario

2008\06\29@175740 by Carl Denk

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I believe most rain gages use a "tipping bucket" (bucket is very small).
There is a funnel above, and a teeter totter sort of arm with a bucket
(maybe a fluid oz. capacity) on each end of arm with the pivot or
fulcrum at the center. When  a bucket which is on the higher elevation
end fills to some point where the weight forces that bucket down, and
the other bucket rises which also moves it in position to receive the
funnel outlet flow. Count the number of times the teeter toter flipped,
and you have the rain quantity. When the bucket is in the lower
position, the water overflows the low side, emptying. The buckets are
inverted wedge shaped, when in the high position hold a known quantity
of water, and in the low position, one side of the wedge is slightly
sloped down from level to empty completely.

The gauge must be self emptying, otherwise could require emptying at
most inconvenient times. Also if your temperature can get below
freezing, needs heat.

See: http://www.raingauge.net/
and google rain gauge. There are inexpensive units under $50, some
wireless including LCD indicator. I think a little searching would find
the sensor by itself. Hardly worth the effort to build, maybe buy a
sensor and build the circuit to interface with PC..

Dario Greggio wrote:
> What would be the best method to measure quantity of fallen rain? (meteo
> station)
>
> A cup/glass and two resistive bars? possibly using AC instead of DC to
> prevent oxidation? Or any other suggestion?
> And, does it need to be emptied once in a while?
>
> TIA everybody.
>
>  

2008\06\30@000130 by Mohit Mahajan (Lists)

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Dario,

How about a cheap load cell to measure the weight of the rain collected?
Calibrate the measurement depending on the volume of the collection
vessel. Just do a Google check on what the density of rain water is. I'd
suspect close to distilled water. It is distilled water after all :-).
Although it may have collected a lot of SPM & gases on its way down.

HTH,
Mohit Mahajan.

Dario Greggio wrote:
> What would be the best method to measure quantity of fallen rain? (meteo
> station)
>
> A cup/glass and two resistive bars? possibly using AC instead of DC to
> prevent oxidation? Or any other suggestion?
> And, does it need to be emptied once in a while?
>
> TIA everybody.
>

2008\06\30@001402 by Mohit Mahajan (Lists)

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To empty the vessel, you could use a heater mounted below the vessel
base to evaporate all the water. Rules out a battery based system,
though. Will work with the 24V system that you are planning to use. :-)

HTH,
Mohit Mahajan.

Dario Greggio wrote:
> What would be the best method to measure quantity of fallen rain? (meteo
> station)
>
> A cup/glass and two resistive bars? possibly using AC instead of DC to
> prevent oxidation? Or any other suggestion?
> And, does it need to be emptied once in a while?
>
> TIA everybody.
>

2008\06\30@142123 by Herbert Graf

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On Sun, 2008-06-29 at 22:44 +0200, Dario Greggio wrote:
> What would be the best method to measure quantity of fallen rain? (meteo
> station)
>
> A cup/glass and two resistive bars? possibly using AC instead of DC to
> prevent oxidation? Or any other suggestion?
> And, does it need to be emptied once in a while?

The "tipping bucket" method is very common. I've got two rain guages
that use it and the only time they don't work is when the temp goes
below freezing...

TTYL

2008\06\30@162732 by Andre Abelian

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face
Best method is IR. http://www.oedes.com/how_rt_works.php

Andre




-----Original Message-----
From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf
Of Herbert Graf
Sent: Monday, June 30, 2008 11:21 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE][PIC] best method to measure rain qty

On Sun, 2008-06-29 at 22:44 +0200, Dario Greggio wrote:
> What would be the best method to measure quantity of fallen rain?
(meteo
> station)
>
> A cup/glass and two resistive bars? possibly using AC instead of DC to

> prevent oxidation? Or any other suggestion?
> And, does it need to be emptied once in a while?

The "tipping bucket" method is very common. I've got two rain guages
that use it and the only time they don't work is when the temp goes
below freezing...

TTYL

2008\06\30@212118 by Jim Korman

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Mohit Mahajan (Lists) wrote:
{Quote hidden}

Give this a look, widely used technique.......

http://www.edcheung.com/automa/rain.htm

Jim


'[EE][PIC] best method to measure rain qty'
2008\07\01@032517 by Dario Greggio
face picon face
Jim Korman wrote:

> Give this a look, widely used technique.......
>
> http://www.edcheung.com/automa/rain.htm

This is nice Jim :)
I'll consider it.

--
Ciao, Dario

2008\07\01@043803 by Alan B. Pearce

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>The "tipping bucket" method is very common. I've got two rain guages
>that use it and the only time they don't work is when the temp goes
>below freezing...

At which point,is it still raining, or some other form of precipitation ???
;))

The other method I have heard of for very light rainfalls is to have a
funnel with a fine outlet that will cause droplets of water, and to use an
optical method for counting droplet rate. Once the rainfall gets to a point
where the droplets become close to a continuous stream then there is
probably a high enough rainfall to measure with the bucket method.

2008\07\01@100338 by Herbert Graf

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On Tue, 2008-07-01 at 09:35 +0100, Alan B. Pearce wrote:
> >The "tipping bucket" method is very common. I've got two rain guages
> >that use it and the only time they don't work is when the temp goes
> >below freezing...
>
> At which point,is it still raining, or some other form of precipitation ???
> ;))

Hehe, well, to be really nitpicky, it CAN still be rain, we call it
"freezing rain" (I think americans call it sleet?). It happens when the
ground temperature is below zero but there's a layer of air that isn't,
meaning it comes down as rain and freezes soon after hitting the ground.
Really nasty to drive in, really beautiful to see the result the next
morning, all the trees covered in a thin sheet of ice. Unfortunately you
get enough of it and your power infrastructure comes down, as happened
in southern Quebec a few years ago.

But aside from that, yes, can't really call it rain anymore if it's
below zero... :)

TTYL

2008\07\01@112511 by Chris Smolinski

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>Hehe, well, to be really nitpicky, it CAN still be rain, we call it
>"freezing rain" (I think americans call it sleet?). It happens when the
>ground temperature is below zero but there's a layer of air that isn't,
>meaning it comes down as rain and freezes soon after hitting the ground.
>Really nasty to drive in, really beautiful to see the result the next
>morning, all the trees covered in a thin sheet of ice. Unfortunately you
>get enough of it and your power infrastructure comes down, as happened
>in southern Quebec a few years ago.

Yes, we call the above freezing rain in the USA. Sleet is when the
precip falls already in the form of ice, usually along with rain and
sometimes snow. Much less dangerous.  I live on the Mason Dixon line,
and in the winter we're often at the right (or is that wrong?)
temperature to get the dreaded "wintry mix" of rain, snow, sleet, and
freezing rain. It starts out as one, and progresses through the other
various precip types.

--

---
Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com

2008\07\01@122010 by Carl Denk

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I think the USA automated weather stations (at many airports) report all
precipitation in inches of liquid since depth of snow can vary over a
wide range for a given amount of liquid precipitation, so some heat is
appropriate. Though as far a I am aware, snow depth is always a human
observation using a measuring stick. Incidentally,  some of the extremes
I have encountered over the years, many times in Atlanta with temps as
low as 15F, and Moose factory, Ontario on James Bay the temp was 96F.

Herbert Graf wrote:
{Quote hidden}

2008\07\01@124835 by Paul Hutchinson

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> -----Original Message-----
> From: piclist-bouncesspamKILLspammit.edu On Behalf Of Alan B. Pearce
> Sent: Tuesday, July 01, 2008 4:36 AM
>
> The other method I have heard of for very light rainfalls is to have a
> funnel with a fine outlet that will cause droplets of water, and
> to use an
> optical method for counting droplet rate. Once the rainfall gets
> to a point
> where the droplets become close to a continuous stream then there is
> probably a high enough rainfall to measure with the bucket method.

Actually this is exactly backwards, once the droplet rate through the funnel
meets or exceeds the mechanical tip rate, the gauge starts reading wrong due
to missed rain during the tip. As the flow increases the error rate goes up,
this is why tipping bucket rain gauges have a maximum inches/hr rate at
which the accuracy applies but no minimum rate to achieve the accuracy. The
minimum rate to achieve accuracy is solely determined by the evaporation
rate of the rain in the buckets. Since the bucket contents are well shielded
from wind and sun the evaporation rate is very low.

FWIW a common pitfall when designing a rain gauge is to use too small of a
collection diameter. Anything less than 8 inches in diameter will have
substantial errors in certain types of rain conditions. A simple test of
this principal is to put out various diameter flat bottom containers and
record the rainfall in each container over the course of a number of storms.
You will find that all containers greater than 8 inches in diameter will be
in good agreement. Smaller diameter containers will have differing
inaccuracies. These tests were done thoroughly back a century ago and
account for the minimum diameter requirements from WMO and NWS.

Paul Hutch

2008\07\01@125737 by Dave Tweed

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Carl Denk wrote:
> I think the USA automated weather stations (at many airports) report all
> precipitation in inches of liquid since depth of snow can vary over a
> wide range for a given amount of liquid precipitation, so some heat is
> appropriate. Though as far a I am aware, snow depth is always a human
> observation using a measuring stick.

Snow depth can be automated as well, using, e.g., sonar. However, some
types of fluffy snow don't give a particularly good surface return. For
one example of this, see p. 16 in Circuit Cellar issue #214 (May 2008).

For most applications, such as calculating runoff, the mass is the most
relevant measurement, and this is most easily accomplished in liquid form.

-- Dave Tweed

2008\07\01@154821 by Peter Todd

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On Tue, Jul 01, 2008 at 12:48:33PM -0400, Paul Hutchinson wrote:
> FWIW a common pitfall when designing a rain gauge is to use too small of a
> collection diameter. Anything less than 8 inches in diameter will have
> substantial errors in certain types of rain conditions. A simple test of
> this principal is to put out various diameter flat bottom containers and
> record the rainfall in each container over the course of a number of storms.
> You will find that all containers greater than 8 inches in diameter will be
> in good agreement. Smaller diameter containers will have differing
> inaccuracies. These tests were done thoroughly back a century ago and
> account for the minimum diameter requirements from WMO and NWS.

!! So, rain doesn't always fall in a random pattern? I mean, I always
assumed raindrops hitting a surface would hit in a completely random
fashion. What you saying sounds like more than just sampling error due
to a small, literally, sample size.

- --
http://petertodd.org 'peter'[:-1]@petertodd.org
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2008\07\01@223750 by Paul Hutchinson

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> -----Original Message-----
> From: .....piclist-bouncesKILLspamspam.....mit.edu On Behalf Of Peter Todd
> Sent: Tuesday, July 01, 2008 3:47 PM
>
> On Tue, Jul 01, 2008 at 12:48:33PM -0400, Paul Hutchinson wrote:
> > FWIW a common pitfall when designing a rain gauge is to use too
<snip>
>
> !! So, rain doesn't always fall in a random pattern? I mean, I always
> assumed raindrops hitting a surface would hit in a completely random
> fashion. What you saying sounds like more than just sampling error due
> to a small, literally, sample size.

Sorry if it sounded like more, it is simply an insufficient sample size
error.

Rain collector diameters of 8 inches or more collect a statistically
significant sample suitable for a 1% accurate, 0.01" resolution rain gauge.

Paul Hutch

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