Topic: Is a wired anemometer better than wireless.......

[BeaverMeadow]

...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).

[Bushman]

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.

[CW2274]

It makes no difference, the update interval is 2.5 to 3 seconds either way.

[johnd]

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.

[CW2274]

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?

[BeaverMeadow]

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?

[CW2274]

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.

[Mattk]

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.   

[ValentineWeather]

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.

[johnd]

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.

[PaulMy]

(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

[ValentineWeather]

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? 

[mcrossley]

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.

[CW2274]

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.

[cpufrost]

Wired is going to have a continuous connection and in theory should provide a continuous stream of data.
It's still up to the designer on how this data is captured and displayed, however.

It IS possible to have gusts/max speed values displayed or recorded with low interval (transmit) rates.  The instrument itself must store and forward values.
Also if you want the absolute max wind value (which is always higher than the standard three second gust) an ultrasonic or other zero inertia instrument is required.  Three cup anemometers do accelerate pretty quickly but in specialized environments they will lag and overhang (overspeed) true wind speeds.  None of that is really relevant to a home user though.

[Garth Bock]

Real time wind speed....old school......
https://www.worthpoint.com/worthopedia/heathkit-vintage-weather-station-id-428744589

Real time wind speed....new school....
https://www.scientificsales.com/Maestro-Brass-Wind-Speed-and-Wind-Direction-Set-p/maestro.htm

[johnd]

Wired is going to have a continuous connection and in theory should provide a continuous stream of data.
It's still up to the designer on how this data is captured and displayed, however.

No, there's really no difference between wired and wireless, at least not down to timescales of one revolution of the wind cups (say 22ms at 100mph wind).

To measure wind speed this relatively simple design of anemometer still has to count the number of revolutions of cups in a finite period and that period is what limits exactly how 'real-time' any reading might be. Of course there are other, more sophisticated anemometer designs, but it's difficult to imagine any non-specialist design for which a wireless signal wouldn't perform just as well as wired.

[Mattk]

Some appear to be getting confused with the blurb, like instantaneous wind speed, wind speed is always something in the past, there is no other way as the principles of motion have not changed as velocity is related to distance and time, no time then there is no velocity. Time remains a variable even with Ultrasonic and most conform to WMO standards.

Like in the case of some Ultrasonic sensors, wind Gust is the highest 3 second average of the wind speed within the last 10 minutes with the 3 second averages based over 250ms values with the values updated/outputted as some additional time interval. This thinking that somehow anemometers measures instantaneous wind speed somehow in real time is totally false ... again and always will be     

[cpufrost]

No, there's really no difference between wired and wireless, at least not down to timescales of one revolution of the wind cups (say 22ms at 100mph wind).

To measure wind speed this relatively simple design of anemometer still has to count the number of revolutions of cups in a finite period and that period is what limits exactly how 'real-time' any reading might be. Of course there are other, more sophisticated anemometer designs, but it's difficult to imagine any non-specialist design for which a wireless signal wouldn't perform just as well as wired.

Typically though it's done for power limits.  I mean true wireless designs have VERY limited power available so the sensor isn't going to post often and only take a reading at said interval.  That's horrible for accuracy with something as dynamic as wind.

With a wire this limit is effectively removed, the instrument is getting mains power and can sample/report in real time.

The compromise is to still sample continuously and then post results and it's perfectly acceptable to have relatively long times between posts as gusts/max values will still be captured.  The downside is the operator cannot see them happen in real time.  This still needs more power as the sensor (whether optical disc driven by anemometer cups or an ultrasonic device) has to be running all the time.

The ideal solution is to have the telemetry near the base of the tower with solar array capable of providing enough power to maintain the batteries through the darkest periods and enough battery capacity to provide full power for 30 days (of insufficient or zero solar production) or so.  Instruments wired to this hub and it transmits to a land based logger.  All online and with direct outputs for continuous monitoring as needed.  In this way, I agree there is no distinction between wired and wireless.  It's just not practical to do for hobbyist/prosumer stations due to cost reasons.  A dedicated DIY'r can do it of course.

[galfert]

Mattk thank you that excellent post. The same response ran through my head before I read your post. You are a good science minded person. Great explanation for a concept which is sometimes a difficult thing to try and teach.

[cpufrost]

I do miss my Heathkit hardware.

If anything, a wireless station cannot bring harmful DC currents inside during lightning storms.

Here are my observations regarding time vs. wind:

With my autonomous station (link in sig), I can go right to the biggest gust/peak and watch recorded video (we have 12 security cameras around the property) and the wind noise heard matches the data displayed.  Practically to the second.  That's what I expect.

Now the TEMPEST system, while its points are five minutes apart and generally useless for this comparison, shows "live" data updated every 3 seconds.  It looks similar to watching a Davis console.  HOWEVER, if I'm actually watching another anemometer via video (the video feed is live with less than 50ms latency) it certainly does NOT match up.  I suppose this is to be expected.  But I don't like it.  I was at a business that has a (Davis) 6163 and during a wind storm you could hear the steel roof panels rattling, trash cans flying around, etc.  And the wind was 57 and gusted to 86 (mph!) just a second later.  Kind of scary as one would expect.

I'm moving the TEMPEST soon and plan to actually test the anemometer with some ALNOR gear not really for accuracy but to see how much of a delay there is.  They don't publish this stuff.  And sadly, I'm sure the delay is dynamic which makes things even worse.

Hope this makes sense.