Author Topic: Is a wired anemometer better than wireless.......  (Read 1139 times)

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Offline BeaverMeadow

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Is a wired anemometer better than wireless.......
« on: May 20, 2018, 03:02:15 PM »
...because the display of wind speed would be real-time and not just a sampling every x seconds?

I couldn't find an answer to this question. I know Davis has wired and wireless anemometers (being discussed currently on the Davis forum) but no mention of this possible difference.

I don't like missing gusts or getting inaccurate averages from my wireless entry level cheap pws and would consider a wired anemometer (if financially feasible).


Online Bushman

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Re: Is a wired anemometer better than wireless.......
« Reply #1 on: May 20, 2018, 03:35:07 PM »
I could be wrong, but IIRC the Davis anemometer is just the connection to the ISS.  And IMO a wired would be truly real-time; not sure if that is better or not.  Inspeed makes some wired ones that show realt-time wind.

Offline CW2274

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Re: Is a wired anemometer better than wireless.......
« Reply #2 on: May 20, 2018, 03:49:14 PM »
It makes no difference, the update interval is 2.5 to 3 seconds either way.

Offline johnd

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Re: Is a wired anemometer better than wireless.......
« Reply #3 on: May 20, 2018, 04:44:10 PM »
There's no difference between wired and wireless in the Davis systems - they all measure the mean wind speed over 2.25 seconds, ie a gust speed. This fits in with what the WMO define as a gust speed and so to all intents and purposes all Davis anemometers measure real-time wind speed.

There's maybe a separate discussion to be had about measuring instantaneous wind speed; that's not a reading that is commonly used but could be estimated by eg timing one rotation of the wind cups.
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Offline CW2274

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Re: Is a wired anemometer better than wireless.......
« Reply #4 on: May 20, 2018, 04:54:47 PM »
they all measure the mean wind speed over 2.25 seconds, ie a gust speed. This fits in with what the WMO define as a gust speed and so to all intents and purposes all Davis anemometers measure real-time wind speed.
Thanks for the clarification. If I understand right, the sample is taken over a 2.25 second stretch then broadcast every 2.5 to 3 seconds?

Offline BeaverMeadow

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Re: Is a wired anemometer better than wireless.......
« Reply #5 on: May 20, 2018, 06:25:06 PM »
If the Davis reporting time is 2.5 seconds regardless of wired or wireless that would be acceptable to me even if not an instantaneous (real-time) response. My Acurite 5 in 1 gives 18 second updates which is what annoys me especially during high wind and gust events.

Does Davis update the display's wind speed every 2.5 seconds or is this just the sampling rate with a longer lag time for the display?

Offline CW2274

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Re: Is a wired anemometer better than wireless.......
« Reply #6 on: May 20, 2018, 06:35:39 PM »
Does Davis update the display's wind speed every 2.5 seconds or is this just the sampling rate with a longer lag time for the display?
It transmits every 2.5 to 3 seconds, per the manual. For instance, if you hear a gust, it's visible on the console, WL, ect. after it's sampled and transmitted, which is about 5 seconds at most.

Online Mattk

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Re: Is a wired anemometer better than wireless.......
« Reply #7 on: May 20, 2018, 07:16:06 PM »
We know what most mean when they state they want "real-time" or "instantaneous" but put in perspective the wind speed at an instantaneous point in time is really zero, as for there to be wind speed the wind speed and wind run has to be measured over a period of time, similar with real-time, speed is based over a period of time in the past, similar with gust, it is measured over a period of time, it simply has to be.   

Online ValentineWeather

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Re: Is a wired anemometer better than wireless.......
« Reply #8 on: May 20, 2018, 07:25:20 PM »
I've always liked the slight delay myself and never understood the thinking of needing realtime to the exact second. The registered speed doesn't change but as mentioned hearing big gust allows time to watch console.
Randy

Offline johnd

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Re: Is a wired anemometer better than wireless.......
« Reply #9 on: May 21, 2018, 09:41:54 AM »
Thanks for the clarification. If I understand right, the sample is taken over a 2.25 second stretch then broadcast every 2.5 to 3 seconds?

Yes that seems to be the picture. When you really start to look at the detail then one or two wrinkles appear like the difference you've highlighted between the 2.25sec and the 3sec (if you had an anemometer on ID #8) periods. AFAIK these aren't explained in any technical documentation that I'm aware of.

Presumably the ISS data packet contains the latest available gust speed, but if the previous gust window closed eg  0.4 sec into the data cycle then I suppose that previous gust speed value would be missed. (Which is maybe a good reason for always having the anemometer on ID #1 to minimise this loss.)  And it's never quite clear how timing of each new LOOP packet ties in with reception of the wind packets - I suspect that the two aren't directly synchronised.
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Offline PaulMy

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Re: Is a wired anemometer better than wireless.......
« Reply #10 on: May 21, 2018, 10:14:48 AM »
Quote
(Which is maybe a good reason for always having the anemometer on ID #1 to minimise this loss.)
I have heard that each higher station ID number is 1/16th seconds longer interval - i.e. station #2 1/16 longer than #1, station #4, 3/16 seconds longer.

Enjoy,
Paul

Online ValentineWeather

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Re: Is a wired anemometer better than wireless.......
« Reply #11 on: May 21, 2018, 01:29:01 PM »
This has something to do with wind and using separate ISS issue developed with wind dash out.
At my residence station I'm running 3 ISS's with temp/hum/rainfall setups only 2 with tipping buckets, 1 ISS with soil temps and 1 ISS strictly wind. Recently added solar to primary ISS ID #1.

This wind issue started dashing out for about hour daily almost immediately after adding solar to system. 
I think the console was so busy it sometimes skips the #6 transmitter, let me explain why.
I have two different VP2 consoles the issue only occurred packet loss with which ever console had the data logger running. The other console would never lose the wind transmitter and kept 97% packets throughout day.  (Both had updated latest firmware) I switched consoles back and forth twice and got the exact repeat every morning.

After moving wind from #6 transmitter ID to #2 transmitter ID it hasn't reoccurred and its been about 5 days now with wind on the #2 transmitter.

Wondering if anyone else has experienced /heard anything like this, where the transmitters at top are getting priority over the lower? 
« Last Edit: May 21, 2018, 06:41:40 PM by ValentineWeather »
Randy

Offline mcrossley

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Re: Is a wired anemometer better than wireless.......
« Reply #12 on: May 21, 2018, 06:23:34 PM »
We know what most mean when they state they want "real-time" or "instantaneous" but put in perspective the wind speed at an instantaneous point in time is really zero, as for there to be wind speed the wind speed and wind run has to be measured over a period of time, similar with real-time, speed is based over a period of time in the past, similar with gust, it is measured over a period of time, it simply has to be.   
Not necessarily ;) Only if you use a measuring device that relies on counting intermittent signals. If you use another type of mechanism such as a hot wire, or an analogue voltage from a rotating cup sensor, or pressure in a pitot tube etc.1 Or even rotating cups with a high number of counts per revolution.

1 Though you could argue there is still a response time, for our purposes it is instantaneous.
Mark

Offline CW2274

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Re: Is a wired anemometer better than wireless.......
« Reply #13 on: May 21, 2018, 06:37:12 PM »
Wondering if anyone else has experienced /heard anything like this, where the transmitters at top are getting priority over the lower?
My anny's been on #2 from day 1 (about 6 years now) and I've never knowingly had a drop, ever.

 

anything