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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#31
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xmetman Wrote in message:
On Wednesday, 10 February 2016 15:04:08 UTC, JohnD wrote: "xmetman" wrote in message ... I suppose the Vantage Pro just collects 1 minute mean speeds and graphs those values in its own LCD display, and it's down to the display software on the PC to take the average of 10 of those one-minute values to produce a 10 minute mean. A one minute mean of 67 mph would be significantly higher than a 10 minute mean (~x1.2 or more higher). ==================== Is it a VP you have (aka VP1 nowadays) or a VP2? If so, it might explain the apparent default to small cups - that's not the been the default for a long time. (Not that it makes a huge difference, it's just a different second-order LUT that's applied for correcting speed vs direction AIUI to account for effects of the anemometer arm geometry. But why would you suppose that it collects 1-min means rather than averaging out the full set of 2.5 sec gust values that are the values actually measured? Hi John I know in the electronics it must collect data and average it out somehow, but as a programmer as far as I can see, the minimum resolution of the raw data it stores is 1 minute and not 2.5 seconds. All the data logger is collecting for wind speed I imagine is the number of revolutions that the anemometer cups make in 2.5 secs, and it would be a good idea if these values were accessible (even if was just for the last 10 minutes) before they were thrown away. snip that's why I would like to see that kind of raw 2.5 second data It is available, Bruce. Davis publish details of their serial protocol, and there is software available (Cumulus for example) that uses it. Now there's a programming challenge for you! -- Freddie Pontesbury Shropshire 102m AMSL http://www.hosiene.co.uk/weather/ http://twitter.com/PontesburyWx for hourly reports ----Android NewsGroup Reader---- http://usenet.sinaapp.com/ |
#32
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xmetman Wrote in message:
On Thursday, 11 February 2016 10:31:53 UTC, Freddie wrote: xmetman Wrote in message: On Wednesday, 10 February 2016 15:04:08 UTC, JohnD wrote: "xmetman" wrote in message ... I suppose the Vantage Pro just collects 1 minute mean speeds and graphs those values in its own LCD display, and it's down to the display software on the PC to take the average of 10 of those one-minute values to produce a 10 minute mean. A one minute mean of 67 mph would be significantly higher than a 10 minute mean (~x1.2 or more higher). ==================== Is it a VP you have (aka VP1 nowadays) or a VP2? If so, it might explain the apparent default to small cups - that's not the been the default for a long time. (Not that it makes a huge difference, it's just a different second-order LUT that's applied for correcting speed vs direction AIUI to account for effects of the anemometer arm geometry. But why would you suppose that it collects 1-min means rather than averaging out the full set of 2.5 sec gust values that are the values actually measured? Hi John I know in the electronics it must collect data and average it out somehow, but as a programmer as far as I can see, the minimum resolution of the raw data it stores is 1 minute and not 2.5 seconds. All the data logger is collecting for wind speed I imagine is the number of revolutions that the anemometer cups make in 2.5 secs, and it would be a good idea if these values were accessible (even if was just for the last 10 minutes) before they were thrown away. snip that's why I would like to see that kind of raw 2.5 second data It is available, Bruce. Davis publish details of their serial protocol, and there is software available (Cumulus for example) that uses it. Now there's a programming challenge for you! -- Freddie Pontesbury Shropshire 102m AMSL http://www.hosiene.co.uk/weather/ http://twitter.com/PontesburyWx for hourly reports ----Android NewsGroup Reader---- http://usenet.sinaapp.com/ Hi Freddie I've already written it! As far as I know, even using the Davis API you can only access minute data, and most of the time this is fine, but as I said in my reply, sometimes it would be good to get at the 2.5 second data that the 1 minute wind speeds are derived from. Well I've written software that talks to the VP directly via the serial port, and it downloads something known as "loop" packets. These contain the real-time data. I know that Davis supply a DLL for accessing the VP. I think that downloads the loop packets too. -- Freddie Pontesbury Shropshire 102m AMSL http://www.hosiene.co.uk/weather/ http://twitter.com/PontesburyWx for hourly reports ----Android NewsGroup Reader---- http://usenet.sinaapp.com/ |
#33
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"xmetman" wrote in message
... All the data logger is collecting for wind speed I imagine is the number of revolutions that the anemometer cups make in 2.5 secs, and it would be a good idea if these values were accessible .... As Freddie rightly says, these 2.5sec values are available in the real-time or LOOP data from the logger (see the Serial Tech Ref for further details). But you must poll and process them on some external device as they become available otherwise they are indeed lost as discrete packets. The shortest interval records that can be stored in the logger for later retrieval are indeed 1-minute - maybe this is what you're thinking of? (Actually, IIRC wind speeds are actually measured over a 2.25 sec gating period at the ISS and then the latest available value transmitted at 2.5625 sec intervals on a VP2 set to channel #1 (it's a progressively different interval on other channels)). I realise that my Vantage Pro is coming up for 12 years old this April OK, so that is likely to be an original VP (VP1). So the transmission interval (channel #1) is indeed 2.5 secs on these older stations. but I would like to think that with technology such as the Raspberry Pi, that either Davis or someone else would be able to put together a cheaper weather station The problem with the RPi is its power demand (say 2W continuous). Most users want a wireless sensor transmitter that is not tied to an external power supply so that there's much more flexibility on where the sensors can be located in order to achieve optimum sensor exposure (and of course no need to worry about running a vulnerable cable out to the sensors). This is just not compatible with anything as power-hungry as an RPi, at least not without a solar panel PSU potentially costing as much as the weather station. It's why microcontrollers rather than microprocessors are usually used in the sensor transmitter - these allow a continuous power budget of maybe 20-30mW, which is compatible with a small/affordable solar panel PSU running 24/7/365 even at higher latitudes. Personally I've always thought that the anemometer has always under read.. That's going to be related at least in part to height and exposure, although if you still have the original anemometer then the bearings will also be seriously worn by now. Examples of the 7911 and 6410 VP1/VP2 anemometers are calibrated in different orientations in wind tunnels to 150mph. This is necessary to generate the lookup tables that are used to correct the measured wind speed for the smallish errors in raw speed caused by the wind flow from different directions interacting with the anemometer arm. John Dann www.weatherstations.co.uk |
#34
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"Freddie" wrote in message ...
John, what is the expected lifetime of VP2 anemometer bearings? If I had to estimate, I'd suggest eg 5 years at an average inland/lowland location. Coastal locations are typically going to be windier and have at least some salt spray in the air. Actually the 6410 anemometer design was revised some 2-3 years ago, in part with new lower-friction bearings (for enhanced responsiveness at low wind speeds) and TBH there hasn't been enough field experience with the new design to get a real idea of whether expected longevity is any different. But I'd hope that at least 5 years was going to be the benchmark again. JGD |
#35
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On 11/02/2016 16:20, JohnD wrote:
"Freddie" wrote in message ... John, what is the expected lifetime of VP2 anemometer bearings? If I had to estimate, I'd suggest eg 5 years at an average inland/lowland location. Coastal locations are typically going to be windier and have at least some salt spray in the air. Actually the 6410 anemometer design was revised some 2-3 years ago, in part with new lower-friction bearings (for enhanced responsiveness at low wind speeds) and TBH there hasn't been enough field experience with the new design to get a real idea of whether expected longevity is any different. But I'd hope that at least 5 years was going to be the benchmark again. JGD Just get a Dines Pressure Tube Anemograph! I'm sure the output could be digitised by some clever script kiddy! Ah well, maybe not - there would be a lot of kit to be incorporated. Does anyone know if any are still in use? |
#36
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On Thursday, 11 February 2016 03:26:26 UTC, Jim Kewley wrote:
In message , Graham Easterling writes Ho hum, welcome to winter 2015/16. We've been having this sort of thing since November. -- Cheers Jim Well, not quite, the peak swell height reached 19m! at the wave hub yesterday, with a significant wave height near 35' You don't 'often' get that sort of thing anywhere. Graham Penzance No not round the Isle of Man, there's not enough fetch on the sea for the waves like that to build up. We've certainly had similar wind speeds on several occasions though, not to mention rainfall. In this SE/SW centric group it's never noticed, reading this place you'd think the world revolves round SE London, Devon and Cornwall. Hence my impatience with people calling this winter boring. -- Jim I live in SE London Jim and I haven't to my knowledge moaned about winter so far and I can't think of anyone else who does; live in SE London that is. |
#37
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On Thu, 11 Feb 2016 16:20:42 -0000, "JohnD"
wrote: If I had to estimate, I'd suggest eg 5 years at an average inland/lowland location. Mine's been going for seventeen years! -- Alan White Mozilla Firefox and Forte Agent. By Loch Long, twenty-eight miles NW of Glasgow, Scotland. Webcam and weather:- http://windycroft.co.uk/weather |
#38
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"Alan White" wrote in message
... Mine's been going for seventeen years! That's excellent and I didn't mean to imply otherwise - there are some individual anemometers that just seem to go on forever, but others that might start giving problems after eg 4-5 years. No obvious rhyme nor reason just individual variation. But I thought the question here was more about when the bearings might start to wear sufficiently so as to start introducing a degree of error into the reading and that's where the very approximate estimate of 5 years comes from. Alan, I guess if you tried rotating the spindle carefully by hand then you might be feeling some roughness in the action compared to a new one. |
#39
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"JohnD" Wrote in message:
"xmetman" wrote in message ... All the data logger is collecting for wind speed I imagine is the number of revolutions if you still have the original anemometer then the bearings will also be seriously worn by now. John, what is the expected lifetime of VP2 anemometer bearings? I know it will depend on how windy the location is - but a ballpark figure would be useful if available. -- Freddie Pontesbury Shropshire 102m AMSL http://www.hosiene.co.uk/weather/ http://twitter.com/PontesburyWx for hourly reports ----Android NewsGroup Reader---- http://usenet.sinaapp.com/ |
#40
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"JohnD" Wrote in message:
"Freddie" wrote in message ... John, what is the expected lifetime of VP2 anemometer bearings? If I had to estimate, I'd suggest eg 5 years at an average inland/lowland location. Coastal locations are typically going to be windier and have at least some salt spray in the air. Actually the 6410 anemometer design was revised some 2-3 years ago, in part with new lower-friction bearings (for enhanced responsiveness at low wind speeds) and TBH there hasn't been enough field experience with the new design to get a real idea of whether expected longevity is any different. But I'd hope that at least 5 years was going to be the benchmark again. JGD Thanks John. I asked the question because my VP2 anemo is nearly 9 years old, and was wondering when I might need to get my wallet out! No sign of any low bias in the readings as yet! -- Freddie Pontesbury Shropshire 102m AMSL http://www.hosiene.co.uk/weather/ http://twitter.com/PontesburyWx for hourly reports ----Android NewsGroup Reader---- http://usenet.sinaapp.com/ |
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