Topic: Trying to choose...

[stego]

I've been looking at the Davis and Peet lines (but wouldn't rule out others).

I'm interested, primarily, in logging peak wind gusts at a remote tower site.  So I'm not keen on a system that logs data at fixed intervals (where the interval might miss a peak gust).

I'd like a wired system, as I'm a ham, and am leery of RFI.

I'd like the anemometer to be mountable separately from the rest of the sensors (e.g., the rain gauge).  I'd like to position the anemometer near the top of a 150' tower, so the cable run will be something over 200' to get it indoors.  (And, obviously, I'd like the anemometer to be durable...)

(I'd also like the current data to be internet-accessible.  But I gather there are lots of options - at least for the most common stations.)

Advice?

Thanks,

/Bill
Portland, OR

[SlowModem]

Davis has an anemometer transmitter accessory, so you could put your anemometer anywhere and have your other sensors on the ground. (of course, it would be wireless).

[kray1000]

I'm interested, primarily, in logging peak wind gusts at a remote tower site.  I'm not keen on a system that logs data at fixed intervals (where the interval might miss a peak gust).

I'd like a wired system, as I'm a ham, and am leery of RFI.

I'd like the anemometer to be mountable separately from the rest of the sensors (e.g., the rain gauge).  I'd like to position the anemometer near the top of a 150' tower, so the cable run will be something over 200' to get it indoors.  (And, obviously, I'd like the anemometer to be durable...)

(I'd also like the current data to be internet-accessible.  But I gather there are lots of options - at least for the most common stations.)  Advice?

Bill
Portland, OR

I don't believe the wireless Vantage Pro 2 units have many issues with RFI.  Given that length of cable run, the maximum wind speed you would actually record with a wired system would be reduced.  That far above ground, you won't miss many gusts.  And although you probably don't get many lightning storms, running a wire from the top of a 150' tower inside the cottage would be "asking for it" if a storm ever did pass through.

Personally, I'd get a wireless Vantage Pro 2 (6152) and the anemometer transmitter kit (6332).  Depending on how you are able to get the data to the Internet, you would also need either the WeatherLink for APRS (6540) or the WeatherLinkIP (6555) datalogger.

[SLOweather]

Questions:

While you want to see the gusts, which implies a short sampling period, how rapidly do you want that data to appear on a web site? Is seeing the gust in near-real time important, or is seeing a graph of the gusts for the last X minutes OK?

Is there Internet available at the transmitter site?
 
As a ham, have you considered sending the data out via APRS? APRS would preclude rapid Internet uploads or you'll overload the local network. But, it does show gust info.

My KD6DSI weather....

[stego]

Thanks for the helpful posts.

A novice question - why would a long anemometer cable run reduce the actual wind speed I could record?

(I’ve got bigger lightning-attractors than the anemometer, so that’s way down on my worry list.)

There is internet available at the transmitter site.  And I don’t need to see the gust data in real-time, but I want peaks captured so I can review the data later.  (I’m a ham, but haven’t really considered sending the data out via APRS.)

Is the ability to catch gust measurements more a function of software capabilities than hardware instrumentation?

Tnx,

/Bill

[kray1000]

A novice question - why would a long anemometer cable run reduce the actual wind speed I could record?

Someone else could explain the technical reasons better than I could, but just to prove I'm not making it up, here's something I found at Davis:

Use Standard 4-Conductor Extension Cable.  Maximum wind speed reading decreases as length of cable from anemometer to console (including junction box cable) increases.  At 140' (42m), maximum speed is 175mph (78m/s).  At 240' (73m), maximum is 140 mph (62m/s).  At 340' (103m), maximum is 70mph (31m/s).  The accuracy of the reading below the maximum is not affected.

So at 200 feet, you should be able to record 150 mph or better... higher than I thought originally.  At those speeds, you'd have bigger problems than whether the anemometer still works.

Is the ability to catch gust measurements more a function of software capabilities than hardware instrumentation?

I would say hardware.  The wireless Davis would transmit the real-time speed about every 2.5 seconds, but again, at 150' you won't miss many gusts.

[SLOweather]

Thanks for the helpful posts.

A novice question - why would a long anemometer cable run reduce the actual wind speed I could record?

It probably has to do with the frequency of the reed switch closure at high MPH, and the impedance/transmission line characteristics of the line itself. As I recall, if you exceed the max wind speed for a given line length, the measured speed won't just level off there, it will become lower and more random...

There is internet available at the transmitter site. 

How fast do you want Internet updates? How reliable is the site power? Solar/mains/back-up gennie? How often do you get up there?

And I don’t need to see the gust data in real-time, but I want peaks captured so I can review the data later.  (I’m a ham, but haven’t really considered sending the data out via APRS.)

Is the ability to catch gust measurements more a function of software capabilities than hardware instrumentation?

Hardware/firmware, rather than software...

An analog system like a cup-driven generator and a voltmeter readout, will have minor lags in measuring speed due to cup/generator inertia and needle lag on the meter.

OTOH, any digital system will have some sampling period over which it measures the wind speed by counting either pulses over time, or counting cycles of an oscillator between switch closures. Most are the former.  They may also have a time delay between sampling periods.

As previously noted, Davis samples and sends wind speed every 2.5 seconds, so the wind speed is "averaged" over that time.

I believe the NWS criteria for gust is the highest wind recorded in a 10 minute period. That's what most of the programs seem to do. They bang on the Davis console every 2.5 seconds or less looking for the wind speed, to extract the highest as the gust. It's also what we have our WeatherElement data hub do.