Hi,
As an experiment I mounted a 15 cm (6 inches) diameter funnel above the FO rain sensor to give a nominal 0.1 mm resolution. I believe the normal definition of a wet/dry day is if => 0.2 mm of rain falls, so the 0.3 mm of the FO is not really "good enough". Particularly as in my experience, it sometimes can be prone to a single "false tip" when the morning sun strikes it, which might affect a "record" for the longest period of wet or dry days.
However, the funnel did not necessarily give any earlier warning of the onset of rain, because the water droplets tended to hang on the funnel sides, unless treated with a surface-tension-reduction coating such as "Rain-X". Another potential issue is that a very high rate of rainfall may "overload" the see-saw (which "loses" some water whilst it is actually tipping), but "splash out" is a well-known issue with the basic FO rain sensor anyway.
For the first onset of rain the hydreon RG-11 is rather interesting with a discussion here. It can emulate a tipping bucket with a resolution down to 0.0001" (0.1 mil) or even 0.001mm ! But I don't believe the absolute (overall total) accuracy is (or could be) as high as a well-maintained tipping bucket. It also requires a local power supply so it is not suitable to use with most pure battery-operated sensor/transmitter systems, but this might not be a major issue for a Weatherduino-based station.
Cheers, Alan.
(09-05-2017, 04:45)danner Wrote: Can any rain gauge actually measure 0.1mm of rain? I would think the bucket tip would require a lot more rain than 0.1mm.
As an experiment I mounted a 15 cm (6 inches) diameter funnel above the FO rain sensor to give a nominal 0.1 mm resolution. I believe the normal definition of a wet/dry day is if => 0.2 mm of rain falls, so the 0.3 mm of the FO is not really "good enough". Particularly as in my experience, it sometimes can be prone to a single "false tip" when the morning sun strikes it, which might affect a "record" for the longest period of wet or dry days.
However, the funnel did not necessarily give any earlier warning of the onset of rain, because the water droplets tended to hang on the funnel sides, unless treated with a surface-tension-reduction coating such as "Rain-X". Another potential issue is that a very high rate of rainfall may "overload" the see-saw (which "loses" some water whilst it is actually tipping), but "splash out" is a well-known issue with the basic FO rain sensor anyway.
For the first onset of rain the hydreon RG-11 is rather interesting with a discussion here. It can emulate a tipping bucket with a resolution down to 0.0001" (0.1 mil) or even 0.001mm ! But I don't believe the absolute (overall total) accuracy is (or could be) as high as a well-maintained tipping bucket. It also requires a local power supply so it is not suitable to use with most pure battery-operated sensor/transmitter systems, but this might not be a major issue for a Weatherduino-based station.
Cheers, Alan.