Fine Offset w8681 (1080/1) Rainfall detector

beteljuice · **Posted:** Mon Dec 07, 2009 1:12 am

Something wrong there - that amount of error with that mod suggests that you were OVER reporting to start with ?

Please define "vertical sided tin" - is that a real calibrated intrument or .......

and certainly, as you may have read elsewhere on the forum, Your rain bucket should be fixed securely (preferably NOT on a mast), and the drain holes shouldn't be exposed to any kind of updraft.

werribee_au · **Posted:** Tue Dec 29, 2009 9:51 pm

Hi Andy,
Where is the rain gauge located? When mine was on the pole it was reporting much rain when there was only wind. I took it off the pole and mounted it (With the stand off bracket), found it better but still got some phantom rain. I now have secured it by the base onto a solid mount for a number of months now and havent had any phantom readings since.

Just climbed up the ladder and checked the diameter of the funnel again and about 86mm dia is what I have, I am reasonablly happy with the reporting. Although I think it reads a little more in heavy rain and a little less in light rain. I guess that it is the nature of the construction and quality of the Fine Offset w8681 (1080/1) Rainfall detector.

Gerard

hills · **Posted:** Tue Dec 29, 2009 11:54 pm

Has anyone considered making the catchment area for the rain gauge 10 times the size of the original and modifying Cumulus to accomodate this so that you get .03mm increments instead of .3mm increments in rainfall?

or perhaps make it 3 tmes the size to get .1mm increments?

beteljuice · **Posted:** Wed Dec 30, 2009 12:28 am

The beteljuice modified his LaCrosse rain bucket to x10 so that he could tell very light rain (actually it doesn't quite work like that for reasons various).

You naturally have to inform Cumulus of what you have done, else all your totals are wrong !

BUT Cumulus still works (ie. rounds) to its 'normal' decimal point (0.1mm / 0.01in), You can see the difference on your station console and you should have improved any tolerance error, but you won't see that extra decimal point resoloution in Cumulus.

hills · **Posted:** Wed Dec 30, 2009 12:58 am

Ah ok. I assume my fine offset WH1091 registers .3mm each time the rain gauge empties as that's how much rain registered when I accidentally moved it the other day. Therefore I thought making it 3 times the size would make sense.

Anyway, as I live in the driest state in Australia, the driest continent on the planet, I probably won't get to test this for quite a while.

Gina · **Posted:** Thu Dec 31, 2009 12:31 am

I was thinking of increasing the size so that it would register light showers, which it misses at the moment. Only problem might be overload in a deluge. Does anyone know the maximum rainfall rate the present unit will take?

Gina · **Posted:** Sun Jan 03, 2010 9:46 am

I think I've got the answer to that myself. Yesterday when I was trying new positions for the temperature and rain gauge I got interference from an electric fence - a pulse about once per second and that gave a rainfall reading (1000mm/hr) something like a hundred times the UK record! I figure the buckets and electronics are well able to cope with anything we might get in this country with a 3x increase in catchment area.

hills · **Posted:** Sun Jan 03, 2010 11:41 am

here's what I built. Its just a funnel cut back to a 13.8cm diameter glued into a container I had lying around. It just sits over the existing gauge. I also have a manual rain gauge so if we ever get any rain I'll see how close it is. My calibration is .33

andyjrb · **Posted:** Tue Jan 12, 2010 6:55 pm

I discovered the other day that my rogue 0.3mm readings, which occurred on very still days, were due to birds landing on it (the gauge is near the bird feeder)

Gina · **Posted:** Tue Jan 12, 2010 10:28 pm

I've nearly finished my modified rain gauge. I'll take a photo of it tomorrow. Only other thing I want to do to it is add a thermostat controlled heater to melt snow and stop icing up. Circuit designed, now I need a couple of components and to make it up. Snowing heavily here and has been since late afternoon.

zaax · **Posted:** Wed Dec 08, 2010 12:42 pm

Look like the rain sensor is a built in problem with the magnet and reed switch (and spiders which were doing loop-the-loop last night when I was changing the battries).

http://www.digitalham.co.uk/equipment/Watson_W8681.php

SUBYDAZZ · **Posted:** Wed Dec 08, 2010 3:41 pm

I'd just like to point out rainfall isn't uniform even over a very small area. It can vary quite a bit (try putting out a few gauges of the same type in a particular area). In the PWS photo shown here, wouldn't the rain catcher be shaded somewhat by the close proximity of the rest of the station to it anyway, giving yo less accuracy with wind blowing from certain directions?

Gina · **Posted:** Wed Dec 08, 2010 3:43 pm

I've placed mine well away from the other sensors and from trees and bushes etc.

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Fine Offset w8681 (1080/1) Rainfall detector

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