Topic: VP2 tipping spoon raingauge?

[miraculon]

The NovaLynx and CoCoRaHS are only about 3 ft apart. Just enough to get the mower in between them.



The ISS is on the other side of the yard, maybe 20' away.

I have seen good agreement on all three when winds are calm and the rain was "straight down". The wind currents around the house and garage wreak havoc with snow accumulation in the winter.

I used the NovaLynx calibrator for the NovaLynx gauge. I checked the VP2 back when it had the original rain cone and tipping-buckets, but I have not repeated it since. I made multiple back-to-back runs on the NovaLynx gauge when I calibrated it to ensure that it was repeatable. There was some discussion in the CoCoRaHS thread about under catch in that gauge a while back.

Because they have agreed from time-to-time, I attribute the variation to wind currents and my substandard siting.

Greg H.

[drew1021]

Definitely check the accuracy of the VP2 when you get a chance and post the results. I can see how the gauges proximity to the house would wreck havoc on totals during windy rain or snow events.

[DRoberts]

Thunderstorm with little wind early Friday morning. Results:

VP2 (tipping spoon)  .13
CoCoRaHS Stratus    .12

[Mattk]

Personally, I'd have said 4.28ml (for a 0.2mm spoon @ (0.200/0.254)*5.44). This is not to nitpick over decimals but more to suggest one shouldn't be too optimistic about the degree of accuracy that's achievable with this sort of calibration. For instance, I'm not completely convinced about the accuracy of the 544ml baseline figure - it does depend on exactly how you measure the funnel rim diameter, what happens when raindrops hit the rim etc.

And I bet a cheap syringe is not accurate to better than 1-2%, if that. If I was going to use the syringe approach then I'd probably weigh the syringe  on a sensitive 100g digital balance (which are available quite cheaply, and even with calibration weights, and sold for jewellery and other uses) before and after achieving a (pre-wetted) tip. I suspect that's going to give a more accurate weight/volume.

Overall, I think nothing beats field comparison over time against a good reference gauge like Stratus/CoCoRaHS or better.

You're correct, even med syringes are not super accurate. https://chemistry.stackexchange.com/questions/41119/what-is-the-accuracy-of-medical-syringes

Typically a 1mm syringe is only used to do/check a ball park adjustment, not a calibration as such and this only takes a few minutes initially as opposed to a full type calibration where you make take an hour or so using 425mm (which is the amount I use), top off the last full tip with a syringe then calculate the % error, adjust accordingly and re-run the whole process again, sometimes at a faster rate, sometimes a slower rate.     

[drew1021]

We had a real frog strangler here last night with the following results

Stratus.       2.88
Vp2.          2.97

Assuming the new spoon assy's accuracy is the same as the old tipper then this result is within spec at 3%

[DRoberts]

 One of our more decent soaking rains here.

 VP2 (spoon)  early 6:45 a.m. .14"     6:35 p.m.  1.00"   (total 1.14")
 CoCoRaHS (stratus)   "          .15"            "          .93"   (total 1.08")

Wind: Average less than 10 mph entire period

Gauges are located about 30 feet apart.

I cannot think why the disparity in the totals developed during course of 12 hours.

Ideas anyone?

[WheatonRon]

 One of our more decent soaking rains here.

 VP2 (spoon)  early 6:45 a.m. .14"     6:35 p.m.  1.00"   (total 1.14")
 CoCoRaHS (stratus)   "          .15"            "          .93"   (total 1.08")

Wind: Average less than 10 mph entire period

Gauges are located about 30 feet apart.

I cannot think why the disparity in the totals developed during course of 12 hours.

Ideas anyone?

Not too surprised. I have concluded the spoon tipper has a mild wet bias, which in my view, is a positive. After several readings over the weeks testing the old tipper with the new tipper both only inches apart from my CoCo gauge is the basis for my conclusion. I think 30 feet apart could cause the abnormalities you had but all in all not bad. Tear down the goal posts and wait for the VP3! Your life expectancy is 110 years old, right?

[CW2274]

Without a doubt, I think rainfall is the most difficult to truly measure accurately with present technology (comparatively speaking with other paramaters), just too many variables. Very high and low humidities are next in line.

[lightmaster]

 One of our more decent soaking rains here.

 VP2 (spoon)  early 6:45 a.m. .14"     6:35 p.m.  1.00"   (total 1.14")
 CoCoRaHS (stratus)   "          .15"            "          .93"   (total 1.08")

Wind: Average less than 10 mph entire period

Gauges are located about 30 feet apart.

I cannot think why the disparity in the totals developed during course of 12 hours.

Ideas anyone?

I have seen it where it was an outright downpour in the field on the other side of my road, and no rain at all in my yard, and I could easily place a rain gauge in the field getting 1+ inches of rain, and a rain gauge in my yard getting no rain at all, but they'd still be less than 30 feet apart. If the distance is more than a few feet, there's no guarantee the 2 gauges will actually get the same amount of rain, much less record the same.

[lightmaster]

Completely contrary to what I just said, my VP2 and 4" Stratus are about 150ft apart (cuz I'm not climbing a barbwire fence every day to go empty the Stratus, lol). Just had a very quick downpour (4.07in/hr for like 5 mins) and here are the comparisons:

VP2:       0.25"
Stratus: 0.22"

[havtrail]

 One of our more decent soaking rains here.

 VP2 (spoon)  early 6:45 a.m. .14"     6:35 p.m.  1.00"   (total 1.14")
 CoCoRaHS (stratus)   "          .15"            "          .93"   (total 1.08")

Wind: Average less than 10 mph entire period

Gauges are located about 30 feet apart.

I cannot think why the disparity in the totals developed during course of 12 hours.

Ideas anyone?

Mother Nature is fickle?

Umm, what disparity? Both totals in the range of 6 or 7 percent apart.

Rich K.

[DRoberts]

 One of our more decent soaking rains here.

 VP2 (spoon)  early 6:45 a.m. .14"     6:35 p.m.  1.00"   (total 1.14")
 CoCoRaHS (stratus)   "          .15"            "          .93"   (total 1.08")

Wind: Average less than 10 mph entire period

Gauges are located about 30 feet apart.

I cannot think why the disparity in the totals developed during course of 12 hours.

Ideas anyone?

Mother Nature is fickle?

Umm, what disparity? Both totals in the range of 6 or 7 percent apart.

Rich K.

Yes. But it is still a disparity. Just worries the scientific side of me. 

[DRoberts]

Completely contrary to what I just said, my VP2 and 4" Stratus are about 150ft apart (cuz I'm not climbing a barbwire fence every day to go empty the Stratus, lol). Just had a very quick downpour (4.07in/hr for like 5 mins) and here are the comparisons:

VP2:       0.25"
Stratus: 0.22"

It's the barbwire fence that is causing it. 

[lightmaster]

Another good shower today. Not sure if I said before but I am using the new single spoon assembly.

Rain start: 3:40pm
Rain stop: 3:51pm
Stratus: 0.45"
VP2:.      0.45"

[johnd]

Perhaps worth noting that the tipping spoon VP2 variant is still not generally available yet - at least, we cannot order them for UK users. I'm curious as to whether they're available in other territories? (I'm talking about full VP2 stations here, not tipping spoon assemblies as spare parts.)

[WheatonRon]

Some additional measurements for a 20 minute rain event today.

CoCo gauge .18
Rainwise gauge 111–.18

The above two gauges were inches apart.

CWOP CW5020, VP2 with new spoon tipper—.35
CWOP FW3075, VP2 with old tipper—.19
CWOP FW4350, VP2 with old tipper—.18

The above 3 VP2 stations are on the same fence maybe 20 feet apart, and about 50 feet away from the CoCo and Rainwise gauges.

I thought the new spoon tipper was reading a bit wet, but these differences are clearly more than a “bit wet”, puzzling to say the least. Per MesoWest, most of the “extra rain” came during a 5 minute span. Not sure what these differences mean but as stated previously, puzzling is a good word.

[WheatonRon]

Some additional measurements for another 20 minute rain event today.

CoCo gauge .38
Rainwise gauge 111–.33

The above two gauges were inches apart.

CWOP CW5020, VP2 with new spoon tipper—.53
CWOP FW3075, VP2 with old tipper—.28
CWOP FW4350, VP2 with old tipper—.32

The above 3 VP2 stations are on the same fence maybe 20 feet apart, and about 50 feet away from the CoCo and Rainwise gauges.

Consistent with prior post, new spoon tipper is over reporting rainfall, at least in a heavy rainfall. Be interesting to see how things play out in a several hour gradual rain event.

[openvista]

Ron, have you verified that the spoon is clean and level? For instance, a dirty spoon will tip sooner than a clean one.

[WheatonRon]

Ron, have you verified that the spoon is clean and level? For instance, a dirty spoon will tip sooner than a clean one.

Excellent suggestions, but after the first rain event, I took the rain cone off and ensured the spoon was clean. It was but I cleaned it again. Something is clearly wrong and yes the ISS is level.

[johnd]

Perhaps worth noting that the tipping spoon VP2 variant is still not generally available yet - at least, we cannot order them for UK users.

T think this comment is still relevant. It does rather suggest to me that Davis is possibly not happy with the spoon design and is either continuing to conduct some extended accuracy trials or conceivably even reviewing the spoon design.

[WheatonRon]

Perhaps worth noting that the tipping spoon VP2 variant is still not generally available yet - at least, we cannot order them for UK users.

I think this comment is still relevant. It does rather suggest to me that Davis is possibly not happy with the spoon design and is either continuing to conduct some extended accuracy trials or conceivably even reviewing the spoon design.

John you may be right (you usually are) but when I buy a product with the Davis name on it, I expect the new or revised product to have been properly field tested. To have these kind of results is troubling and when I consider my problems over the recent years with the SHT31 makes me feel even worse. I, and many other participants in this Forum would be happy to help field test, if Davis would just ask. Don’t treat us end users as an after-thought. And Davis, try and keep the key resellers of your world (e.g., Johnd and Ryan Wilhour of Scaled Instruments) informed on new product developments and enhancements such that they can intelligently communicate them with people like me, end users.

[johnd]

John you may be right (you usually are) but when I buy a product with the Davis name on it, I expect the new or revised product to have been properly field tested.

Well, yes. But my point is that as far as I'm aware the TS VP2 gauge has not been officially released by Davis as yet and so one can't assume that testing is complete. If Ryan sees this then maybe he can clarify the status in the US for example. But I'm not aware of any official launch or promotion more generally for the TS part, which I would expect to see with a new product release.

If I had to guess, it would be that Davis are reasonably advanced in their plans to announce the TS part with part numbers etc assigned and have manufactured a substantial pre-production batch, a few of which inadvertently made it to Australia last year with some more released into the US spares market, but without being part of the full official launch. This is just a guess and ICBW but it has echoes of the launch of the SHT15 T/H sensor (the .174 sensor part) a couple of years back which was available in EU VP2 stations but only for a short while and also as a spare in the US, but was then superseded by SHT31 before ever making it into full production.

[Mapantz]

Well, yes. But my point is that as far as I'm aware the TS VP2 gauge has not been officially released by Davis as yet and so one can't assume that testing is complete. If Ryan sees this then maybe he can clarify the status in the US for example. But I'm not aware of any official launch or promotion more generally for the TS part, which I would expect to see with a new product release.

If I had to guess, it would be that Davis are reasonably advanced in their plans to announce the TS part with part numbers etc assigned and have manufactured a substantial pre-production batch, a few of which inadvertently made it to Australia last year with some more released into the US spares market, but without being part of the full official launch. This is just a guess and ICBW but it has echoes of the launch of the SHT15 T/H sensor (the .174 sensor part) a couple of years back which was available in EU VP2 stations but only for a short while and also as a spare in the US, but was then superseded by SHT31 before ever making it into full production.

I see that weatherspares now have the spoon tipper for sale so I might purchase it. Although, I should add 'reluctant' in to that as it's not worth £56 in my opinion.

[weather34]

Well, yes. But my point is that as far as I'm aware the TS VP2 gauge has not been officially released by Davis as yet and so one can't assume that testing is complete. If Ryan sees this then maybe he can clarify the status in the US for example. But I'm not aware of any official launch or promotion more generally for the TS part, which I would expect to see with a new product release.

If I had to guess, it would be that Davis are reasonably advanced in their plans to announce the TS part with part numbers etc assigned and have manufactured a substantial pre-production batch, a few of which inadvertently made it to Australia last year with some more released into the US spares market, but without being part of the full official launch. This is just a guess and ICBW but it has echoes of the launch of the SHT15 T/H sensor (the .174 sensor part) a couple of years back which was available in EU VP2 stations but only for a short while and also as a spare in the US, but was then superseded by SHT31 before ever making it into full production.

I see that weatherspares now have the spoon tipper for sale so I might purchase it. Although, I should add 'reluctant' in to that as it's not worth £56 in my opinion.

go for it tina its where i got mine , problem these days anything  USA made,imported  is dramatically more expensive just the way it is these days..anyway he is a nice guy to deal with ..brian

[WheatonRon]

Well, yes. But my point is that as far as I'm aware the TS VP2 gauge has not been officially released by Davis as yet and so one can't assume that testing is complete. If Ryan sees this then maybe he can clarify the status in the US for example. But I'm not aware of any official launch or promotion more generally for the TS part, which I would expect to see with a new product release.

If I had to guess, it would be that Davis are reasonably advanced in their plans to announce the TS part with part numbers etc assigned and have manufactured a substantial pre-production batch, a few of which inadvertently made it to Australia last year with some more released into the US spares market, but without being part of the full official launch. This is just a guess and ICBW but it has echoes of the launch of the SHT15 T/H sensor (the .174 sensor part) a couple of years back which was available in EU VP2 stations but only for a short while and also as a spare in the US, but was then superseded by SHT31 before ever making it into full production.

I see that weatherspares now have the spoon tipper for sale so I might purchase it. Although, I should add 'reluctant' in to that as it's not worth £56 in my opinion.

go for it tina its where i got mine , problem these days anything  USA made,imported  is dramatically more expensive just the way it is these days..anyway he is a nice guy to deal with ..brian

I have the non-metric version of this tipper, part no. 7345.425 vs. the one being sold by weatherspares, part no. 7345.147. While easy to change-out the old rain tipper in the VP2 ISS for this new one, I am very disappointed with the inconsistencies when measuring rainfall. Sometimes this tipper over reports rain, sometimes it under reports rain when compared to my CoCo gauge. I would wait until Davis gets the bugs worked out unless the metric version, for whatever reason, doesn’t have the problems the US version has (highly unlikely). For what it is worth, I did a search for both part numbers on the Davis website without a match.