Author Topic: Davis bucket calibration  (Read 4543 times)

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Offline Bashy

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Re: Davis bucket calibration
« Reply #25 on: July 20, 2017, 11:59:16 AM »
The tests were done over a day, takes nearly an hour to empty the bottle, the amount left in the bottle is negligible 
most certainly not the amount that we are looking for, the drip is just off center, prob about 5cm from the hole and
the bottle is sat in the cone, even if  the amount lost due to error is  2 mm (of which theres no chance) it still
wouldnt equate to the amount missing, also the amount missing corresponds to the amount of difference between the
manual 4" and the bucket during rainfall, i know you are trying to find fault, but the test was done 4 times, albeit not
scientifically accurate but accurate with regards to to mount of water used, i have an accurate 60ml syringe marked in
1ml increments, so at i at least say that part is as good as i can get it, there is no way i am loosing  6-8mm during test
Kind regards
Bashy

Offline dalecoy

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Re: Davis bucket calibration
« Reply #26 on: July 20, 2017, 12:27:00 PM »
Not trying to find fault - just trying to understand how you are doing this. 

Offline dalecoy

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Re: Davis bucket calibration
« Reply #27 on: July 20, 2017, 12:40:33 PM »
I do have one suggestion for "verification".  [Perhaps you have already done this]

Do the same test on your manual gauge.  Same bottle, same rate, etc.  [Since you're getting a new bottle, then repeat on your Davis].

Offline Bashy

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Re: Davis bucket calibration
« Reply #28 on: July 20, 2017, 12:50:08 PM »
Not trying to find fault - just trying to understand how you are doing this. 

My bad, sorry, just felt like it..

I do have one suggestion for "verification".  [Perhaps you have already done this]

Do the same test on your manual gauge.  Same bottle, same rate, etc.  [Since you're getting a new bottle, then repeat on your Davis].


Yes, i will try but not sure it will be possible, depends on if i can balance the bottle on it, I will video it next time just to show
whats what :)
Kind regards
Bashy

Offline dalecoy

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Re: Davis bucket calibration
« Reply #29 on: July 20, 2017, 01:26:25 PM »
Yes, i will try but not sure it will be possible, depends on if i can balance the bottle on it, I will video it next time just to show
whats what :)

Oh.  It was a big coke bottle?  [or a small manual gauge?]


Offline Bashy

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Re: Davis bucket calibration
« Reply #30 on: July 20, 2017, 02:55:24 PM »
Yeah, large, well, 1.75L bottles
Kind regards
Bashy

Offline dalecoy

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Re: Davis bucket calibration
« Reply #31 on: July 20, 2017, 03:57:55 PM »
Yeah, large, well, 1.75L bottles

If that won't stand easily in your manual gauge, perhaps the 500mL bottle would work (for both tests, of course).

The important thing is to get as close to "identical" test setups as possible.

Offline CW2274

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Re: Davis bucket calibration
« Reply #32 on: July 20, 2017, 04:16:30 PM »
All I use is a gallon milk jug with a hole poked in the bottom corner. Sits in the cone just fine. Certainly not a NovaLynx calibrator, but a heck of a lot cheaper and it works.
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Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #33 on: July 20, 2017, 05:20:13 PM »
I use the NovaLynx calibrator on 8" gauge, this information may be handy for someone with the 6.5" gauge also. 
If you have a gram scale 1 milliliter (ml) of water weighs 1 gram (g).

Example I use 946ml + container weight= total. It takes about 25 minutes to empty bottle using 1/16" orifice with the NovaLynx calibrator. This is the 6" per/hr rate and works very well for my area. 

NovaLynx has supplied this information on their 6.5" diameter gauge which may be useful. 
Using 1/32 nozzle which is 3.5" per hour they recommend 1.74 tips for the .01 bucket tipper so converting to metric tipper the math for metric gauges. 0.01" of water = 5.44 ml.

So even without the calibrator any jug with hole can simulate something in the ballpark you just won't get the steady flow rate the calibrator provides.
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Offline SLOweather

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Re: Davis bucket calibration
« Reply #34 on: July 20, 2017, 05:47:22 PM »
This only makes sense if the manual gauge and the Davis are the same diameter. For instance, 544 ml should equal 1.00" of rain in a Davis 6.5" tipping bucket, but the same 544 ml volume in a 4" Stratus manual would be 2.72".

I do have one suggestion for "verification".  [Perhaps you have already done this]

Do the same test on your manual gauge.  Same bottle, same rate, etc.  [Since you're getting a new bottle, then repeat on your Davis].

Offline CW2274

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Re: Davis bucket calibration
« Reply #35 on: July 20, 2017, 05:52:29 PM »
So even without the calibrator any jug with hole can simulate something in the ballpark you just won't get the steady flow rate the calibrator provides.
Exactly. My present "hole" starts at 4.5-5" rate (I use rope putty to vary the hole size to get the desired rate) and after an "inch" empties out I'm at about .5 to 1" per hour.
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Offline Mattk

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Re: Davis bucket calibration
« Reply #36 on: July 20, 2017, 06:07:36 PM »
A reasonable feed arrangement can be made using a irrigation dripper, some drippers work ok some don't, it takes a little experimenting to find one that works ok, adjustable for different feed rates which typically need to be 60 minutes plus, the more time allowed will be more typical of most rain rates. For standard Davis cone & 0.2mm tippers run 425ml which should click over a tad under 100 tips, round out to the next tip with a syringe and calc things back from this. 

Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #37 on: July 20, 2017, 06:58:58 PM »
A reasonable feed arrangement can be made using a irrigation dripper, some drippers work ok some don't, it takes a little experimenting to find one that works ok, adjustable for different feed rates which typically need to be 60 minutes plus, the more time allowed will be more typical of most rain rates. For standard Davis cone & 0.2mm tippers run 425ml which should click over a tad under 100 tips, round out to the next tip with a syringe and calc things back from this.

I don't find this true. I started with the slow drip and gauges rarely matched. In fact Novalynx out of California recommends and calibrates all new tipping buckets at 6" per hour rate.

Here is NovaLynx quote: For the rain gauges manufactured by NovaLynx, the factory calibrated flow rate is six
inches per hour, unless otherwise specified.

Another: Factory calibration uses the 1/16" diameter orifice at 6"
per hour for an 8" rain gauge. This rate gives a good overall results.
« Last Edit: July 20, 2017, 07:05:31 PM by ValentineWeather »
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Offline dalecoy

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Re: Davis bucket calibration
« Reply #38 on: July 20, 2017, 07:09:36 PM »
This only makes sense if the manual gauge and the Davis are the same diameter. For instance, 544 ml should equal 1.00" of rain in a Davis 6.5" tipping bucket, but the same 544 ml volume in a 4" Stratus manual would be 2.72".

I do have one suggestion for "verification".  [Perhaps you have already done this]

Do the same test on your manual gauge.  Same bottle, same rate, etc.  [Since you're getting a new bottle, then repeat on your Davis].

Yes, of course - but there is a rather simple calculation (given the diameter of the manual gauge) to convert the measurement.  That would be within reasonable limits.

Offline Mattk

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Re: Davis bucket calibration
« Reply #39 on: July 20, 2017, 08:55:27 PM »
A reasonable feed arrangement can be made using a irrigation dripper, some drippers work ok some don't, it takes a little experimenting to find one that works ok, adjustable for different feed rates which typically need to be 60 minutes plus, the more time allowed will be more typical of most rain rates. For standard Davis cone & 0.2mm tippers run 425ml which should click over a tad under 100 tips, round out to the next tip with a syringe and calc things back from this.

I don't find this true. I started with the slow drip and gauges rarely matched. In fact Novalynx out of California recommends and calibrates all new tipping buckets at 6" per hour rate.

Here is NovaLynx quote: For the rain gauges manufactured by NovaLynx, the factory calibrated flow rate is six
inches per hour, unless otherwise specified.

Another: Factory calibration uses the 1/16" diameter orifice at 6"
per hour for an 8" rain gauge. This rate gives a good overall results.

As we know from many studies and reports tipping gauges are not constant across the range of very low to medium to heavy rain rates. Six inches an hour (2.5mm/minute) is way up there and beyond what most gauges would ever see on any regular long term basis. NovaLynx may do this for some specific reason, have no background with NovaLynx but have spent many hours over many years calibrating & comparing Davis gauges and have enough figures to know what works and what doesn't.

Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #40 on: July 21, 2017, 06:55:25 AM »
A reasonable feed arrangement can be made using a irrigation dripper, some drippers work ok some don't, it takes a little experimenting to find one that works ok, adjustable for different feed rates which typically need to be 60 minutes plus, the more time allowed will be more typical of most rain rates. For standard Davis cone & 0.2mm tippers run 425ml which should click over a tad under 100 tips, round out to the next tip with a syringe and calc things back from this.

I don't find this true. I started with the slow drip and gauges rarely matched. In fact Novalynx out of California recommends and calibrates all new tipping buckets at 6" per hour rate.

Here is NovaLynx quote: For the rain gauges manufactured by NovaLynx, the factory calibrated flow rate is six
inches per hour, unless otherwise specified.

Another: Factory calibration uses the 1/16" diameter orifice at 6"
per hour for an 8" rain gauge. This rate gives a good overall results.

As we know from many studies and reports tipping gauges are not constant across the range of very low to medium to heavy rain rates. Six inches an hour (2.5mm/minute) is way up there and beyond what most gauges would ever see on any regular long term basis. NovaLynx may do this for some specific reason, have no background with NovaLynx but have spent many hours over many years calibrating & comparing Davis gauges and have enough figures to know what works and what doesn't.

I have a little experience calibrating also and know the slower rate calibration doesn't follow my 8" STG and have found the Novalynx recommended calibration works best on both the 8" Texas Electronics and 8" Rainwise.
I stopped chasing the calibration on Davis buckets long time ago because they were all over the place non consistent and unreliable can't recommend to anyone. 
I've never tried the aeroCone and don't plan on it when a quality 8" rainwise replaces and works great. They are consistent and as accurate as many high end buckets if calibrated at 6" per/hr rate.

Edit: I should say this 6" hr rate actually shows about 5 1/2" per the Davis console. Why it works best? I'm not sure, but even after an inch of rain with this calibration I can have zero error or within .02 on the 8". It just works, I was first skeptical and now I understand why they recommend it.
« Last Edit: July 21, 2017, 08:38:12 AM by ValentineWeather »
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Offline weatherc

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Re: Davis bucket calibration
« Reply #41 on: July 21, 2017, 08:34:43 AM »
Six inches an hour (2.5mm/minute) is way up there and beyond what most gauges would ever see on any regular long term basis.

I dis-agree on this, rates more than 150 mm/hr are nothing that unusual during thunderstorms. My record-rainrate, this in south Finland and with 10 years of data, are 400+ mm/hr. Yes, it REALLY rained then  :lol:

Offline Bashy

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Re: Davis bucket calibration
« Reply #42 on: July 21, 2017, 08:43:21 AM »
Six inches an hour (2.5mm/minute) is way up there and beyond what most gauges would ever see on any regular long term basis.

I dis-agree on this, rates more than 150 mm/hr are nothing that unusual during thunderstorms. My record-rainrate, this in south Finland and with 10 years of data, are 400+ mm/hr. Yes, it REALLY rained then  :lol:

I have had this quite regular this summer......
Kind regards
Bashy

Offline Mattk

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Re: Davis bucket calibration
« Reply #43 on: July 21, 2017, 05:49:13 PM »
No, 150mm/h is not normal but you will see intensities higher than this over short periods of time and in Davis's case this is based on timing the tipping bucket but to say it rains 150mm per hour, hour on hour is quite unreasonable so lets differentiate between rain rate and periodic intensity.   

Over 10 minute archives I've seen close to the 20mm mark which is serious intensity (2mm/min) and equiv to ~ 120mm/h but this is not the norm and one won't generally see sustained rainfall like this over extended periods of time which is way tippers should be calibrated for the average mid range expected     

Offline CW2274

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Re: Davis bucket calibration
« Reply #44 on: July 21, 2017, 06:24:59 PM »
but to say it rains 150mm per hour, hour on hour is quite unreasonable so lets differentiate between rain rate and periodic intensity.   
Granted it doesn't happen every day, but if you're under a land falling tropical system, these sustained rates are very reasonable and do happen. If your tipper can handle a 6"/150mm rate accurately and still be at 10% that, why would you not?
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Offline Mattk

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Re: Davis bucket calibration
« Reply #45 on: July 21, 2017, 06:54:35 PM »
95/5 rule. Because you calibrate for 95% of the expected normal average not 5% of the unexpected

Offline CW2274

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Re: Davis bucket calibration
« Reply #46 on: July 21, 2017, 07:24:30 PM »
95/5 rule. Because you calibrate for 95% of the expected normal average not 5% of the unexpected
So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2", don't bother because 2" an hour is good enough. Backwards thinking. I personally ALWAYS strive to get the utmost from my equipment, PWS or otherwise. Why leave accuracy on the table...
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Offline Mattk

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Re: Davis bucket calibration
« Reply #47 on: July 21, 2017, 09:01:25 PM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can? Do you have the figures to prove that statement? Even 50mm/h is above normal as far as rain rates, intensity and duration is concerned.

Re the comment that it may be off 10%, so some are then happy with a 10% inaccuracy 95% of the time ? I don't think so. Maybe can accept 10% inaccuracy 5% of the time?

Offline CW2274

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Re: Davis bucket calibration
« Reply #48 on: July 21, 2017, 09:46:50 PM »
....So by your reasoning even if the tipper can handle 6" an hour just as accurately as 2"
Who said it can?
The people who do this as a profession and respected opinions to back it up. What is your basis?
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Offline ValentineWeather

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Re: Davis bucket calibration
« Reply #49 on: July 21, 2017, 10:02:45 PM »
Even 50mm/h is above normal as far as rain rates, intensity and duration is concerned.


That's less than 2" hr.  Many areas are 3-4" average. Here 5-8" over short periods are common, even much higher occasionally. The rain may continue on for 45 minutes or longer bringing the average way down but most of the rain 80-90% fell during that 10-15 minute (5-8") rate so if you calibrate the gauge at 1-2" guaranteed you see a 20-30% shortage every time it rains.  Been there done that 5-6" rate is perfect for my area.

https://www2.iccsafe.org/states/Virginia/Plumbing/PDFs/Appendix%20B_Rates%20of%20Rainfall%20for%20Various%20Cities.pdf
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anything