Author Topic: Max Vue rain rate  (Read 1763 times)

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Offline BCJKiwi

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Max Vue rain rate
« on: May 05, 2013, 04:54:15 PM »
Hi, been running a Vue / Cumulus setup since the middle of 2012 without issues except...
on two occasions now the system reported very high hourly rain rates.

System is metric (in New Zealand with an NZ model of the Vue - at great expense  :sad:).
It is mounted on the roof of the house and reasonably clear of immediate obstructions - as well as can be expected in an urban environment.
The Vue manual (pg 50) indicates the maximum Rain Rate for the Vue in metric is 1016 mm/hr.
However during two periods of extreme storm conditions (for Auckland New Zealand) with high gusting winds and heavy dumps of rain, the system has recorded a hourly rain rate of 1413 (in December) and again just yesterday of 1260.6 mm/hr. Rain for the day was 66mm.
baro was down at 988, winds gusting over 45km/hr.
We have had almost 1/3rd of the entire years rain so far in the last two days.
Have checked the records of nearby stations an the max was 444 mm/hr.
our highest readings (apart from the two noted above) have been in the 200's.

Any suggestions as to what may be happening and what to do about it?

Thanks

Offline Weather Display

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Re: Max Vue rain rate
« Reply #1 on: May 06, 2013, 02:57:58 AM »
even values in the 400 range are extreme
(that works out at over 6mm per minute)
I recorded 4mm/min max rate here on saturday's rain event (Davis VP)
I presume the values your are quoting are on the console?
(its not all that clear if they are, or in the software)
Brian
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http://www.weather-display.com

Offline BCJKiwi

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Re: Max Vue rain rate
« Reply #2 on: May 06, 2013, 04:50:02 PM »
I was working from the software output.
However I have studied the manual and found the relevant data in the console.
The console shows 1280mm/hr
So I guess this is potentially an issue in the ISS, else we really did get that rate momentarily.
The manual indicates the rate is calculated based 'on the interval of time between each spoon tip' but does not detail what 'based on' really means - i.e. if it averages it over a period. It also indicates that rain data is updated (presumably meaning ISS -> console) at a 20sec interval.

With .2mm per tip, 1280mm/hr  (if my math is right) means 1280/.2 = 6400 tips/hr. 60*60/6400 = 0.56 secs per tip which would appear a reasonable max that would be physically achievable - specially when compared to the specified max of 1016mm/hr = 0.709secs per tip.

Is there further information available on exactly how the rain rate is calculated?

Thanks

Offline johnd

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Re: Max Vue rain rate
« Reply #3 on: May 06, 2013, 04:57:59 PM »
Is there further information available on exactly how the rain rate is calculated?

From AN28:

'RAINFALL RATE
Parameters Used: Rain Total (actually, rain rate is a measured variable in the sense that it is
measured by the ISS and transmitted to the display console, whereas all other calculated
variables are determined by the console from data received from the ISS.)

Formula:
Under normal conditions, rain rate data is sent with a nominal interval of 10 to 12 seconds.
Every time a rain tip or click occurs, a new rain rate value is computed (from the timer values)
and the rate timers are reset to zero.
Rain rate is calculated based on the time between successive tips of the rain collector. The rain
rate value is the highest rate since the last transmitted rain rate data packet. (Under most
conditions, however, a rain tip will not occur every 10 to 12 seconds.)

If there have been no rain tips since the last rain rate data transmission, then the rain rate based
on the time since that last tip is indicated. This results in slowly decaying rate values as a rain
storm ends, instead of showing a rain rate which abruptly drops to zero. This results in a more
realistic representation of the actual rain event.

If this time exceeds roughly 15 minutes, than the rain rate value is reset to zero. This period of
time was chosen because 15 minutes is defined by the U.S. National Weather Service as
intervening time upon which one rain "event" is considered separate from another rain "event".
This is also the shortest period of time that the Umbrella will be seen on the display console
after the onset of rain.
=============================

Not sure that provides much extra illumination, but it's all there is.
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline BCJKiwi

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Re: Max Vue rain rate
« Reply #4 on: May 07, 2013, 03:29:18 AM »
Unfortunately not as that focuses what is happening with low rain rates/rainfall ... UNLESS "Every time a rain tip or click occurs, a new rain rate value is computed" really means a new rate is calculated every tip and the highest then transmitted at the next transmission cycle (which for the Vue is 20secs). If this is the correct interpretation then every extreme would be registered provided the rate was not above than physical maximum the bucket will cycle at.


Offline johnd

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Re: Max Vue rain rate
« Reply #5 on: May 07, 2013, 04:19:49 AM »
UNLESS "Every time a rain tip or click occurs, a new rain rate value is computed" really means a new rate is calculated every tip and the highest then transmitted at the next transmission cycle (which for the Vue is 20secs).

That's certainly how I read it. And I can't easily see an alternative reading. How else would you read it?

Curious that they've doubled the interval for rainfall packets being sent, apparently on both Vue and VP2 stations - must admit that I hadn't noticed that detail had changed - always used to be 10-12 secs, ie as the AN states. But I'm not sure that it makes any significant difference either to this issue or to rainfall readings in general.

Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline BCJKiwi

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Re: Max Vue rain rate
« Reply #6 on: May 07, 2013, 07:51:36 AM »
I'm just reading off the manual that came with the Vue so who knows which is more authorative but I agree that the reporting frequency should not alter the calculation.

However that analysis does suggest the rain rate read may well be 'real' but unbelievable.
I could do what I did the last time which and chop the 1260 down to 260 (or 280). We did get a max rate in the 200s recently.

Offline johnd

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Re: Max Vue rain rate
« Reply #7 on: May 07, 2013, 09:18:29 AM »
I'm just reading off the manual that came with the Vue so who knows which is more authorative ....

All the documentation now seems to say 20 secs (eg specification documents, catalogue etc) so that's presumably the correct figure nowadays. Curious as to why a change was made but most unlikely to be of much significance in practice.

Quote
However that analysis does suggest the rain rate read may well be 'real' but unbelievable.
I could do what I did the last time which and chop the 1260 down to 260 (or 280).

It's difficult to know what might have caused the spurious rate reading (even though it may have been 'real' in the sense that it's a genuine timer-derived reading). If the reed switch is just starting to become faulty then it might conceivably have been contact bounce. Or under extremely high rainfall conditions it's not impossible to think of other theoretical explanations, eg could enough rain water have been splashing around below the buckets to short across the reed switch contacts? Or if water was accumulating in the funnel faster than it could flow out at zero hydrostatic pressure, maybe this somehow could have caused a second very-quick tip?

But ultimately I think you just have to treat this as a curiosity and handle it as you think best. I'm not aware of any known cause for this behaviour and so perhaps one of the ideas above is responsible.

Edit: Sorry, just remembered that this is a Vue and not a VP2, so the 'below the buckets' splashing idea isn't relevant
« Last Edit: May 07, 2013, 09:43:52 AM by johnd »
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline BCJKiwi

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Re: Max Vue rain rate
« Reply #8 on: May 07, 2013, 07:54:38 PM »
I think I will just 'correct the high to a lower value.

This has only happened twice in the time the Vue has been running (10 months) and both occasions were, as previously noted, in periods of very heavy rain combined with high blustery winds.

Thanks for your help John

 

anything