Post by thread:[EE][PIC] best method to measure rain qty

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. > >

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. >

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. >

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

Best method is IR. http://www.oedes.com/how_rt_works.php Andre -----Original Message----- From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@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

Mohit Mahajan (Lists) wrote: {Quote hidden}> 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. >> >> Give this a look, widely used technique....... http://www.edcheung.com/automa/rain.htm Jim

>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.

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

>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

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}> 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 > >

> -----Original Message----- > From: piclist-bouncesKILLspammit.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

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

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 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 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFIaomd3bMhDbI9xWQRAjW0AJ9uPxmgNHDaFbaiR2ECA+S4GVyqCwCdHtEP gg1vuenPEbfvWWdr21WDjgM= =EdiZ -----END PGP SIGNATURE-----

> -----Original Message----- > From: .....piclist-bouncesKILLspam.....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