Raingauge Inaccuracy - Watson W-8681 Fine Offset
Posted: Tue 12 Mar 2019 12:05 pm
I've been running my station now since mid January with no issues regarding the hardware until this last weekend.
We had a storm pass through Cornwall on 10th March and in the evening I recorded gusts of 44 mph with average wind speeds in excess of 25 mph. not unusual for here and I expect we'll have several like this over the year. However I did notice that my rain gauge started to read rainfall when the wind was averaging 20 mph plus and when it dropped below this about 6 hours later the gauge returned to normal, with no readings. During this time there was no actual rainfall at all !. I looked at the gauge which sits on top of a 2.4m tall 100mm square wooden post secured rigidly to a concrete wall . The gauge itself was vibrating along with the plastic arm it is mounted on. I think that there is a point at which the level of vibration upsets the tipping mechanism to give false readings. The fault lies in that the plastic arm to which it is attached is not rigid enough. This is not helped by the fact that the prevailing wind direction is from the west (the Atlantic) and the arm of the rain gauge is at right angles to this ie. north - south.
I had a total rainfall registered that was over 90 mm in six hours when there was none.
So I think that my solution will be to mount the gauge directly off the square wooden post on a rigid metal arm that does not vibrate, about 60 cms below its existing position and then wait for the next storm to see how it behaves.
I don't know if any other enthusiasts have had a similar experience but I pass this on for information.
Regards, Phil
We had a storm pass through Cornwall on 10th March and in the evening I recorded gusts of 44 mph with average wind speeds in excess of 25 mph. not unusual for here and I expect we'll have several like this over the year. However I did notice that my rain gauge started to read rainfall when the wind was averaging 20 mph plus and when it dropped below this about 6 hours later the gauge returned to normal, with no readings. During this time there was no actual rainfall at all !. I looked at the gauge which sits on top of a 2.4m tall 100mm square wooden post secured rigidly to a concrete wall . The gauge itself was vibrating along with the plastic arm it is mounted on. I think that there is a point at which the level of vibration upsets the tipping mechanism to give false readings. The fault lies in that the plastic arm to which it is attached is not rigid enough. This is not helped by the fact that the prevailing wind direction is from the west (the Atlantic) and the arm of the rain gauge is at right angles to this ie. north - south.
I had a total rainfall registered that was over 90 mm in six hours when there was none.
So I think that my solution will be to mount the gauge directly off the square wooden post on a rigid metal arm that does not vibrate, about 60 cms below its existing position and then wait for the next storm to see how it behaves.
I don't know if any other enthusiasts have had a similar experience but I pass this on for information.
Regards, Phil