Author Topic: Anyone currently using the new Davis Sonic Anemometer?  (Read 5730 times)

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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #25 on: September 27, 2022, 02:03:53 AM »
Yes, that is basically what my Lufft Ultrasonic do and based on the principles of Ultrasound I would imagine any ultrasonic does the same?

Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #26 on: September 28, 2022, 02:52:43 PM »
I guess I'm still confused: if the anemometer is using the transducers as the means to measure wind speed and direction via the movement of air across their axes as well as to estimate ambient air temperature via air density, both of which result in variations in sound transit time between the transducers, how does it determine whether any given change in sound transit time is due to the movement of air or the density of the air? Both the Davis and LCJ user manuals make passing reference to temperature measurements being used for calibration but no detail is given. The Davis spec sheet lists what appears to be a simplified "wind speed translation formula" which doesn't include a temperature term at all: V = P(2.25/T) (V = speed in mph, P = no. of pulses per sample period T = sample period in seconds). Sorry if I'm being a dummy here - I'm just a hobbyist with a non-mathematics/technology background who really wants to understand how my new piece of kit actually works!
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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #27 on: September 28, 2022, 03:48:04 PM »
Air density is also a requirement but since relative humidity may not be measured a default factory value is typically used with some systems allowing a user changeable value to be set. Unsure how Davis apply/source humidity or value used? 

Online DaleReid

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #28 on: September 28, 2022, 04:16:57 PM »
I am confused, too.

IF what I read implies that a time of transmission of a known ultrasonic pulse from one post to another on a anemometer is done, then you get:
a) wind speed   I can see that
b) wind direction   I can see that too, just geometry

c) humidity    not if you are getting a and b determined
d) density altitude    not if you don't have a barometer reading and aren't measuring a and b at the same time.


I agree that all those things, speed, humidity and density are factors in accurate measurement of the speed of sound, which is subject to moving through moving air.

You cannot have ONE measurement (time) and get four different values from it. You just can't.  If there is a way, I'm open to seeing a valid mathematical treatment of the subject, but co-variants cannot vary independently and in reverse be uniquely identified without error based on that one measurement which is what I read is being asserted in this discussion.

I have some Vaisala units which measure wind speed and direction with the ultrasonic method (as well as a Met One unit) but the pressure and temp and humidity are measured with separate devices in the unit.

Dale
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Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #29 on: September 28, 2022, 04:42:58 PM »
Dale has described the source of my confusion very nicely. Unless the 6415 contains other sensors which Davis/LCJ make no mention of or the console or weatherlink or whatever does some calculation(s) using data from other separate sensors then I can't understand how it's supposed to work. I also have a 6410 and the speed and direction values from both anemometers correspond reasonably well - though not perfectly as they're situated in different locations - so it does seem to work but how it does that is unclear to me.
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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #30 on: September 28, 2022, 06:33:07 PM »
Ultrasonic anemometers can be a standalone sensor streaming out data so have to be self contained and not reliant on "outside" data. Air Pressure is measured and Air Density is calculated. Relative Humidity is not a biggie and Lufft adopt a factory default of 75% but this can be changed by the user configuration. 

The influence of temperature and humidity on the sonic velocity is compensated by the alternating measurements between each pair (alternating Transmit/Receive) of opposite sensors, the sensor to sensor velocity will be faster down wind as opposed to the velocity up wind.

Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #31 on: September 28, 2022, 08:59:34 PM »
Though I don't understand how it would work, the transducers sending/receiving sounds in a way that compensates for the influence of temperature doesn't seem completely implausible but it would be nice to get some input from someone who does know exactly how the 6415 works. The wording about temperature measurements being used for calibration that Davis/LCJ include in their manuals seems to suggest some other means. I guess I can always contact Davis or LCJ directly...
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Offline WheatonRon

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #32 on: September 28, 2022, 10:04:51 PM »
Though I don't understand how it would work, the transducers sending/receiving sounds in a way that compensates for the influence of temperature doesn't seem completely implausible but it would be nice to get some input from someone who does know exactly how the 6415 works. The wording about temperature measurements being used for calibration that Davis/LCJ include in their manuals seems to suggest some other means. I guess I can always contact Davis or LCJ directly...

If you reside in the US, contact Davis telephone support. If you do not reside in the US, don’t waste your time with Davis email support—too flakey, and not timely.
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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #33 on: September 28, 2022, 10:22:14 PM »
One would doubt if support you could contact at Davis would actually know anyway, or be in a position to detail the interior workings of the 6415?

Online DaleReid

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #34 on: September 28, 2022, 10:31:25 PM »
I have a Campbell Scientific SR50A distance measuring (snow and river depth) device.  It measures distance and being an out of doors unit, has to know the temperature to compensate for the changes in speed of sound with temperature.

One more accurate and more expensive version has a small radiation shield with a temp measuring sensor inside, and can, in some versions, connect directly to the sensor and have that adjustment to the distance made based on the ambient temperature.

Another less expensive unit, the one I have, has none of this, and just reports out the distance as measured by reflected pulse over the round trip.  Yet the manual has several warnings about errors due to not taking temperature into consideration.  The suite of datalogging programs has one which allows you to sent the ambient temperature either to a fixed value (and again notes errors) or by using another temperature sensor for ambient temp and using that value in the final calculation of distance.  Humidity is not a factor for this application, nor is barometric pressure.

The effort by which this research grade instrument is discussed makes it evident to me that temperature is the major factor in error, and the lack of datalogger input of barometric pressure or humidity is a less of an influence.  Yet there are some graduate level papers I have read discussing the measurements of similar devices that go to painful extremes to be as accurate as possible and do include them.  I wasn't able to put my fingers on references while I typed this, all having been something I ran across a couple years ago. 

I am always eager to learn and even if I don't completely understand the discussions in the methods and equipment section of some of those papers, I like to read them to try to expand my understanding somewhat.  Once in awhile after a couple of ultra-precise discussion, the author will say something to the effect that while it is a factor, the maximum influence is a 1/4% or some small number and will be ignored for the rest of this paper's discussion. The author recognizes the science, discusses the magnitude of the effect,  and then if small, chooses to ignore it.

I am amazed at technology and the ways some things are used.  An example that most of us won't run into is a vibrating wire strain gauge, and most descriptions of them will highlight their use to long term stability and repeatable precision. 

And I scratch my head and say, "Who would have thunk it?"

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Online DaleReid

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #35 on: September 28, 2022, 10:36:31 PM »
Mattk :   You raise a good point about customer level support at Davis being able to detail the inner workings of the 6415. 

I had several conversations with a support engineer at RMYoung, and the fellow I was talking with had done some deep work with one of the sensors and data translators I was asking about.  He was a delight to talk with, didn't have a bill I had to pay and may have been a slow day since he was in no rush to move on to the next phone call. 

It all depends upon the day, the tech you talk with and as you mention, whether or not the support supervisors consider it necessary for all their staff to know a certain level of awareness about how things work for their products.  They may only be trained to the level of 'put wire A on connecter B and it should work,' or as I experienced had a very deep level of knowledge which actually surprised me a bit that he knew. 

Dale
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Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #36 on: September 29, 2022, 04:46:36 PM »
For anyone who's interested, I contacted LCJ via email to inquire about the temperature calibration and heard back within a few hours that the anemometer contains a separate temp sensor. Fantastic customer service!
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Online DaleReid

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #37 on: September 29, 2022, 06:00:00 PM »
Buick:  Thanks for doing the work, and also to help understand how their equipment helps make for highest accuracy.
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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #38 on: September 29, 2022, 06:08:49 PM »
Buick: Can you also ask about Air/Relative Humidity & Air Pressure in relation to Air Density?

Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #39 on: September 30, 2022, 04:28:54 PM »
Mattk: I inquired about pressure and humidity and received the following response from LCJ CEO Christophe Michel: "Being a marine electronics engineer, long before our adventure of creating LCJ Sensors, since 1981 for me, I judged that the correction of humidity and atmospheric pressure factors was not useful for the quality/price ratio we wanted to propose."
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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #40 on: September 30, 2022, 07:24:14 PM »
That is interesting as one would have thought Air Density is a critical component in regard sonic velocity through the air? Proper Air Density requires Air Pressure (physical sensor), temperature and Humidity, humidity is not a big deal and temperature can be derived which is the way some mid range Ultrasonic units determine Air Density.

The quality/price obviously would be a factor in terms of range, resolution, accuracy and update rate (? don't have a value for the 6415 update rate) when comparing specs to some of the higher end Ultrasonic.   

Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #41 on: September 30, 2022, 08:20:13 PM »
From Scaled Instruments:

Tentative Specifications

    Output data : ASCII RS422
    Updating data : 1 Hz per second
    Wind module sensitvity: 0,13m/s
    Wind module resolution : 0,05m/s
    Wind module dynamic : 0,13-40 m/s
    Direction sensitivity : +/-1°
    Direction resolution : 1°
    Power Supply : Autonomus with integrated solar pannels and battery
    Electrical consumption : 0 mA
    Operating temperature range without iceeing : -15°C/55°C
    Weight of the head : 100 gr
    Support : Vertical 30 cm
    Diameter : 16 mm in foil

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Offline Mattk

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #42 on: October 01, 2022, 07:45:19 PM »
Some comparison of a mid range ultrasonic which uses a physical onboard Pressure sensor and derives a virtual temperature

Quote
Updating data : 1 Hz per second ...
250 ms, Internal sampling rate 60Hz / Output rate 1-10 seconds user definable
Quote
Wind module dynamic : 0,13-40 m/s ...
0 - 90m/s (324 km/h)
Quote
Wind module resolution : 0,05m/s ...
0.01m/s
Quote
Direction resolution : 1° ...
0.1°

Question might be is it the lack of Air Pressure (quality/price ratio) that restricts the LCJ's accuracy/performance in general and especially in higher wind speeds?

Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #43 on: October 01, 2022, 08:14:42 PM »
Good info and good question - certainly seems possible that deficits in the performance of the LCJ compared to the Lufft could be due lack of integration of pressure data into the output.

I've only been running the 6415 for about a week in benign, if unseasonably warm, weather in northwest Washington state so I can't say much definitively about it's performance compared to the 6410/mechanical anemometer; I'll need a year of side by side comparison before I can give a decent accounting of the relative strengths and weaknesses of the two.

So far, though, the 6415 is clearly more sensitive to lighter winds than the 6410 and its output seems to be quite accurate especially given that the 6410 has a superior exposure at the top of a ~12' mast mounted at one end of the crest of my roof which is ~13' above ground while the 6415 is mounted about ~12' above the ground on a mast ~10m away from the house. The 6410 should be working about as well as it ever has as it was installed new during spring of this year - a replacement of the original installed in fall of 2015.

My initial feeling about the 6415 is that I'm pretty impressed with it and if it continues to perform as well as it has throughout our long, dark rainy season during which my location is exposed to gusts of 40-50mph and occasionally higher on a fairly regular basis, I would consider replacing the 6410 with a 6415...time will tell.
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Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #44 on: October 01, 2022, 08:18:12 PM »
PS: I also inquired about what temp sensor the LCJ uses and was informed that specifics about the hardware are proprietary/confidential. Again, hats off to LCJ customer service!
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Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #45 on: October 01, 2022, 08:24:51 PM »
If anyone has been running a 6415 and a 6410 simultaneously for at least a season I'd be interested in learning about their impressions of how the two compare. I'm happy to post updates here about my experience in doing so if it would be useful/of interest.
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Online DaleReid

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #46 on: October 01, 2022, 09:48:11 PM »
"PS: I also inquired about what temp sensor the LCJ uses and was informed that specifics about the hardware are proprietary/confidential."

Nothing a screwdriver and a sharp knife can't help an inquiring mind find out about!

Just teasing.  I know designs and all, especially circuit design using known commercial components, is costly and reverse engineering is always a concern.

But knowing if the sensor was a precision item or just a guess ball park value would be of legitimate interest for a user.

I think that universities and the government equipment has to or is expected to let the buyer know what's inside so costly evaluation of precision and accuracy doesn't need to be done, and to have some degree of robust function implied.  This isn't always the case, but a couple projects I am aware of (decades ago) the sensors used were very completely described in a response to a request for use bid the U put out.

Anyway, different world, different pocketbook.  I'd venture a guess that the stuff used internally is off the shelf from some major supplier.  Dale
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Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #47 on: October 01, 2022, 10:10:25 PM »
I wouldn't have a problem disassembling one if I had an extra/consumable one! Maybe after I win the lottery...
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Offline Buick

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #48 on: October 24, 2022, 05:29:14 PM »
This is probably not the right thread for this question but I'm going ahead and asking anyway since there's been recent activity here. I found another thread (https://www.wxforum.net/index.php?topic=39485.new#new) from a couple of years ago to which I've also posted this in case someone there happens to respond.

So here goes: I'm running a WLL and 2 Davis VP2 consoles, both of which are updated to firmware version 3.88. I have a 6410 anemometer on channel 2 which is the anemometer that one of the consoles receives from and a recently installed 6415 anemometer on channel 5 which is what the other console receives from. WLL is receiving all data from all transmitters including both anemometers. I have multiple Pro+ subscriptions and can compare data at 1-min intervals between the WLL and the consoles. It appears that the WLL consistently reports higher wind speeds for the 6415 anemometer compared to the console that the 6415 transmits to by about 1mph. The daily maximum wind speed that the WLL has reported for the 6415 is 1mph greater than what the console reported every day since 10/11/22 except for today where the WLL reported a daily max wind speed 2mph greater than the console. During the same period of time, the daily max wind speed reported by the WLL for the 6410 is identical to that reported by the 6410 to the console it transmits to. Had I not come across this thread and also checked to see if there was a discrepancy between the WLL and the console that the 6410 transmits to I probably wouldn't have thought much more about the issue but seeing that others have had somewhat similar experiences the consistency of the discrepancy makes me think that something, while relatively minor, isn't quite right. Why should this oddly consistent, if small, discrepancy exist between the WLL and the console for the 6415 but not between the WLL and the 6410? If anyone has any suggestions or ideas I'm all ears.
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Offline WheatonRon

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Re: Anyone currently using the new Davis Sonic Anemometer?
« Reply #49 on: October 24, 2022, 05:45:38 PM »
Sounds like the perfect question for Davis support. Call them. They are very responsive to calls and know the product, as they should. Email support takes awhile.
« Last Edit: October 24, 2022, 05:50:25 PM by WheatonRon »
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