OK, I also feel this post left a few loose ends, but I still bought my WH40, despite having read all the existing posts at that time.
Like most posters, I've been reasonably happy with my WH40.
As can be seen in a typical chart the increased diameter allows it to detect lighter rainfall than the WS69 and slightly quicker.
Although they can both be slow compared to my leaf wetness sensor.
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More recently, I had a 30 min episode of vertical heavyish rain and next to no wind, that I wasn't so happy with.
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I've been mulling over possibilities for a while.
1. Get a VP2 and run another weewx instance. (I had better luck spending megabucks without the requisite payback, with my old pre-retirement FD than I'd get with the current purse holder). So not a good option, and there are VP2 users using rainwise???
2. Get a rainwise, and use the gpio service to override the WH40 values. (Problem the wires, with 3 German shepherds that like to go rallying round the garden, full opposite lock, handbrake turns, four paw drifts, and crashes. Hence the reason my WH40 is 10 feet up, and why I don't have a Stratus.)
3. Add a collar, I'd fabricate from sheet aluminium, needs to be 110mm high (Can't convince myself this is the main issue and it doesn't address airflow issues)
4. Bond a Davis aerocone to the WH40 funnel (Problems; The Davis users using rainwise. The aerocone is slightly smaller in diameter, so a calibration factor would be required and nothing is known about the supposed firmware algorithm.)
5. Live with what I've got and adjust the WS69 down (without a Stratus I'm reliant on limited data that suggests a factor of about 0.9).
1 and 2 are basically out. 3 and 4 need more info to determine potential effectiveness.
Splash out.
From another post, Gyvate is waiting for some decent rain to test his printed extension.
Tipping bucket.
From info earlier in this thread, then the max rain rate calculates at just under 14 1/2 in/hr.
Rainwise spec 7.8 in/hr, Barani 23 1/2 in/hr
Early in this thread, a degree of emphasis was placed on whether the poor bucket could keep up, and the quoted 50 tips in 49 sec supports that without actually determinig whether that is achievable or what is the actual limiting factor. Early WH40s used a reed switch ( should be good for at least 200cycles/sec ).
So I thought I would try and determine the max rain rate for both gauges, factor in the different collector areas, any other difference (if any) would be the result of any algorithm in the gateway/console firmware.
The max calculated rate for the WH40 equates to 125ml of water in the 49sec reporting interval.
Dumbo here, thought he could get close with a measuring jug and a watch.
How wrong, however, this minor embarrassement did throw up an unexpected result.
My rate wasn't very even (I'm stood on a tall step ladder that wobbled at every opportunity, when I overdid the rate I noticed the bucket stopped ticking).
Out of interest I removed the funnel and slowly poured directly into the bucket, go too fast, and the bucket goes down and stays down until the flow reduces.
Of course this is of no use without an even recordable flow rate.
Now I do have controllable flow rate valves, but they are currently in use as part of my irrigation system in my greenhouses. So a better experiment will be carried out in due course.
In the short term, I decided to see what maximum rate I could persuade the gauges to produce.
I removed the funnels and manualy performed a little finger dance on each bucket.
WS69 WH40 GW WH40 HP2550
RainRate RainRate RainRate
1.189 3.260 3.26
6.291 7.323 7.323
7.016 7.323 7.323
7.016 7.323 7.323
7.016 7.323 7.323
7.016 7.323 7.323
7.016 7.323 7.323
7.016 7.323 4.063
7.016 7.323
6.732 7.323
2.173
Note: I did not achieve 14 1/2 in/hr, but the repeatability suggests to me that I did hit the maximum.
At least any fiddle factor used is the same in both the gateway and the console.
At this stage I'm unsure about the relationship between the WS69 max and the WH40 max, I think I was expecting to see the 2.56 relationship from the difference in diameters
Anyway I'll try to come back with results from a controlled flow on the WH40.
I'll dismount it and clamp to a low table (with the hounds indoors), use various increasing flow rates until I stall the tipper
I'll check dispensed volumes with a kitchen scale.
I hope to determine
1. The true measurable max rain rate
2. The nature of any firmware corrections (if any).
My reasons for this post, are purely selfish, I hate inaccuracy and I hate not knowing how to fix it even more.
So please, feel free to shoot me down in flames.
