How to reset today's rain

[peterh]

I sometimes get strange spikes of rain when there isn't any rain. My current diagnosis is that this is my own mistake... my Fine Offset rain gauge is mounted on the same standard mounting pole as the other sensors. Which is screwed to a wood pole which doubles as a frame for a garden gate.

I've learnt that the gauge works by tipping over when it's filled, triggering a reed switch. So... I figure that if a bird lands on the frame, or if somebody closes the gate, or when there's a gust of wind, it may trigger the switch even though there is no rain.

Now, I know that I can edit my "daily rain", but:
1. the figure for Rain during last 24 hours doesn't change
2. my web site is apparently updated properly, and even Wunderground is update accordingly, but my graphs are still screwed.

Should I worry about this?

[steve]

Cumulus tries to cope with the rain counter going screwy, as it tends to with Fine Offset stations for a number of reasons, but the 'rain last 24 hours' figure is calculated from the values of that counter over the last 24 hours, so it's not trivial to do anything about that. If you want to correct it, you would need to stop Cumulus and edit the values of the 'total rain counter' in the current monthly log file for the last 24 hours.

Similarly, to correct the graphs you would need to stop Cumulus and edit the relevant column of data.

[peterh]

I'm thinking... maybe, just maybe, many instances of "the Fine Offset rain gauge going screwy" may be due to the following:

1. the lack of information on 'how to properly position a rain sensor for reliable operation' in the manual, and
2. the lack of understanding of the user (and that includes yours truly) on how such a device works.

I will kick the wood pole that holds the FO sensor mast a few times somewhere today, and see what this does. I wouldn't be amazed if this would lead to it registering rain spikes.

Maybe, just maybe, an FO rain gauge would work a lot better when it would be used properly.
Which, as far as my current understanding (which may still be rudimentary) tells me, is:

1. Make sure it gets no 'rain shade' (keep it out of wind shade), and
2. Make sure it is not mounted on a base that is prone to vibrate. Which means, don't mount it on the standard mounting pole.

I'm glad that I have a low-tech rain gauge to verify whatever the FO tells me
When I get to construct my permanent sensor setup, I'll make sure to keep the above in mind.

[steve]

Undoubtedly some of the instances of spurious Fine Offset rain measurements will be down to how and where they are mounted. But most of them are down to the design of the gauge (too easily affected by wind, for example) and the fact that they simply 'invent' rain on a dry, calm day, for no obvious reason.

[sfws]

1. the lack of information on 'how to properly position a rain sensor for reliable operation' in the manual, and
2. the lack of understanding of the user (and that includes yours truly) on how such a device works.

As for height etc see FAQ http://wiki.sandaysoft.com/a/FAQ#Where_ ... ain_sensor in the Wiki.

For information about how it works see Gina's post at https://cumulus.hosiene.co.uk/viewtopic.p ... uge#p22328, or for simple description see http://wiki.sandaysoft.com/a/Rain_measu ... Rain_Gauge also in the Wiki, or search the fine offset forum for earlier discussions about such problems.

[peterh]

This afternoon when I got home, I gave the pole to which our sensor setup is mounted a couple moderate pushes... and lo and behold, the FO unit thought that we had an epic spike of 1.2mm of rain in 48 seconds! (that's four tips...). Needless to say, I wasn't soaked when I got in

So.

If you're getting rain spikes on your PWS, check if your rain gauge is susceptible to undue vibration.

[CountryGuy]

The issue with unexplained rain reporting lies with the nature of the rain sensor found with most digital weather stations. Commonly the sensors are designed with a teeter-totter with spoon like depressions at each end. Like any teeter-totter to work properly it must be perfectly level at the pivot point. Therefor, if your sensor is mounted on a pole several feet above the ground the pole must be stabilized by one means or another otherwise wind gusts may cause the sensor to falsely register rainfall accumulation. This being particularly true if your sensor is mounted on the same plane as prevailing winds in your area.

Other things that can cause unexplained rainfall recordings and sometimes recording failures are dust/dirt accumulation in the depressions of the teeter-totter, insects (particularly spiders), and clogged drain (yes there is a drain). All rain sensors are not created equal and some are more susceptible to having issues than others. I have personally found the types with a smaller opening at the top less problematic than those with a full top grid type opening.

[peterh]

... and today, someone else decided to conduct a similar, if somewhat more thorough, experiment. With a large two by four piece of wood, suspended from a small crane... hitting my sensor setup in the back of the skull.

Which made our rain sensor record record an epic spike of 10 mm of rain in one instant. And rendered all wind sensors useless. We now have a constant south wind.

New kit is on its way... the guy who did it, a local farmer, was very upfront about it. The sensors themselves seem ok, but they've just broken off the mast, and the mast is bent too. I suggested to source the parts, but he said "no... order a new kit and send me the bill. I'll take the old stuff and see if I can make it work for myself."
So I offered to help him with fixing it and setting it up, especially with finding a good location for his sensors, and to get him up and running with Cumulus.

[peterh]

The issue with unexplained rain reporting lies with the nature of the rain sensor found with most digital weather stations. Commonly the sensors are designed with a teeter-totter with spoon like depressions at each end. Like any teeter-totter to work properly it must be perfectly level at the pivot point. Therefor, if your sensor is mounted on a pole several feet above the ground the pole must be stabilized by one means or another otherwise wind gusts may cause the sensor to falsely register rainfall accumulation. This being particularly true if your sensor is mounted on the same plane as prevailing winds in your area.

Other things that can cause unexplained rainfall recordings and sometimes recording failures are dust/dirt accumulation in the depressions of the teeter-totter, insects (particularly spiders), and clogged drain (yes there is a drain). All rain sensors are not created equal and some are more susceptible to having issues than others. I have personally found the types with a smaller opening at the top less problematic than those with a full top grid type opening.

Thanks! That is very valuable information!
When the new kit is in, I'll pay close attention to this when I set it up.