Davis™ CWOP pressure problem

[Old Tele man]

OK, I've been fighting the VP2 "barometer" problem ever since my station went "live" on CWOP, and that problem is:

• The VP2 Console generates and displays Sea Level Pressure (SLP) which is raw barometric (data from the sensor) pressure that's been compensated for altitude & temperature (and humidity?). I cannot find an option for displaying either altimeter pressure (ALT) or raw barometeric station pressure (SP).

• The WeatherLink (USB and IP) programs transmit SLP data to CWOP when they should be sending Altimeter (ALT) pressure (what CWOP expects).

So, what is the consensus solution to this Davis pressure problem?

Is the solution to just set the station elevation to zero-feet and "trick" the VP2 console into displaying (and the WL software concurrently transmitting) what amounts to a 100%-uncompensated pressure (SP)?

Or, should I just continually adjust the pressure "offset" to match the SLP pressure values that NOAA / NWS stations display? (seems to be needed almost monthly)?

Too many un-answered e-mails tells me that Davis is not interested in correcting this problem in their WL programs.

Any suggestions, recommendations, or comments?

[Weather Display]

you could use VVPlive or weather display to send the needed ALT pressure to CWOP

[Old Tele man]

Good idea, have somebody ELSE solve Davis's problem, except I have WL-IP -- and no computer -- for data transmittal to both CWOP and WU.

[Bushman]

What if you change the altitude?

[Old Tele man]

What if you change the altitude?

That's the first poll answer of the four selections above.

[Aardvark]

for some odd reason, I do not have that problem.   Initially I had used a variety of barometers, measured the pressure from the ground level outside and compensated for the height difference between where the console in question and where the ground level ( change in elevation)  eventually I was able to acertain what the correct barometric pressure was .  I then  set both the consoles and Envoy to that amount.

I have monitored that and compared it with NWS and the folks that live in the vicinity of this station who have Davis units.  we are in agreement with only difference of a couple of a hundreth of pressure.

My thought on the whole thing,  how do you know your pressure is off.  the exact pressure is not that important unless you are doing a scientific gas experiment that you have to compensate for the pressure difference between the storage device and the out of storage device.

For the rest of us humans (we are from the same planet, right????  )  I would be more concerned at the change in pressure and to the degree of change, rate of change and so forth.

I would do the math, make the elevation calculations and find a comparable device that you can sit on your desk by your console and make the measurement.  Then of course  the factor that your Davis is correct and your comparable device is wrong.... but I don't want that to bug you.

No, this is an interesting topic that I am planning on following and see what happens, what other recommendations come down the pike and what conclusions and solutions, should it need a real solution, is recommended.

Aardvark ( only 19 days and counting until I retire after 30 years of science teaching and research.)

[George Richardson]

"Good idea, have somebody ELSE solve Davis's problem, except I have WL-IP -- and no computer -- for data transmittal to both CWOP and WU."

The only problem is that this is CWOP's problem, not Davis'. Things that are FREE are usually worth what you pay for them. The answer to this problem is to not send data to CWOP.

Davis VP2 is a WEATHER station and Weather people (Meteorologists) use SLP rather than what airports use (altimeter pressure). Now there is a method to this madness. Airport pressures (altimeter) are available to the public FREE, so CWOP has a good base. In fact, the altimeter pressure at any place and at any time within the US can rather easily be calculated using Government provided instruments (not cheap!) We can't have airplanes thinking they are 100' above the mountain top when in fact they are 50' below, SPLAT.

[Old Tele man]

Yes, I am aware of the differences between station pressure SP (QFE), field altimeter ALT (QFE), sea level pressure SLP (QNE). The problem is, that WL-IP is marketed as being compatible with CWOP and WU...and, bluntly, it is NOT. The WL-IP program and ISP website is were the "correction(s)" could/should best be implemented, but isn't.

And, since when was WL-IP "free"? It's marketed and sold as a 'package' comprised of an ethernet-ready IP data logger WITH usage of/access to Davis's WeatherLink hosted website for further data distribution to CWOP, MADIS, WU, and other "end-user" internet sites.

I have NO problem with Davis displaying SLP on the console, but beyond that there's NO user-control or selection of the OTHER pressure formats that are "standard" across the CWOP, MesoWest, and other (WU, etc.) end users. In fact, my concern is centered upon the NOAA / NWS-TUC use and display of "my" weather data--I do not want to be contributing erroneous data!

Oh, and the *reason* why aircraft use 'standardized' ICAO ALT pressure rather than 'corrected' SLP (above 18K I believe) is so that ALL aircraft move UP/DOWN by the same amount (ie: separation distance) regardless of where they fly over. And, meterologists use SLP so that all the myriad pressure inputs from differing altitudes, areas of localized pressures, and differing atmospherics can be converted to "acceptable" rational equivalance. Pressures from Pikes Peak, CO, and San Diego, CA, as well as snowly New England and desert Arizona, have to be rationized to their local atmospheric variables to be comparable. So, they can not simply use a single, one-size fits all, standardized compensation (altitude-only) as aircraft need and use.

[Dr Obbins]

One option missing on the poll is to ignore CWOP quality ratings.

 This is how I look at it. Last summer I purchased an new VP2 console. Davis is a "reputable" company with calibration and it internal quality control systems in place. Using a GPS, I entered the altitude. Now using a local airport as a reference, my reading is with in 0.02 of what I would assume is more "professional" and regularly calibrated equipment (after all this is central KY where the one plane that lands per day relies on this equipment). So I am happy that my readings are as accurate as can be expected with the equipment in use. As Aardvark mentioned, change in the barometer reading is more useful than the actual reading it's self.

Now comparing your readings to the CWOP  is a little risky. Have you looked at the other stations that are close by? How "reputable" are these other stations? Are you comparing your readings with lesser calibrated equipment? Or are you one of the better calibrated stations helping to "clean up" a polluted data pool? Look at the bottom, of this page at some of the other stations in my control group. Currently there is variation from a positive 0.6 to a negative 1.8mb. I take CWOP's ratings with a grain of salt.

[George Richardson]

"Yes, I am aware of the differences between station pressure SP (QFE), field altimeter ALT (QFE), sea level pressure SLP (QNE). The problem is, that WL-IP is marketed as being compatible with CWOP and WU...and, bluntly, it is NOT. The WL-IP program and ISP website is were the "correction(s)" could/should best be implemented, but isn't."

Sorry for my sophomoric lecture to a Phd candidate. I find that very few people in this forum that are bitchin' about CWOP vs Davis are , in fact, aware of differences. I will also defend myself concerning the "free" statement. I thought it was obvious I was talking about the CWOP service (which is becoming quite spotty, at least for me). Finally, I notice that the high-end weather stations still use serial connections which is the way Davis VP started. Also, I thought the latest Davis consoles had a SLP vs Alt. option, maybe I was wrong.

"In fact, my concern is centered upon the NOAA / NWS-TUC use and display of "my" weather data"
I was not aware these people (NOAA / NWS-TUC) used data other than their own.

FWIW

George

[Old Tele man]

Have you looked at the other stations that are close by? How "reputable" are these other stations? Are you comparing your readings with lesser calibrated equipment? Or are you one of the better calibrated stations helping to "clean up" a polluted data pool?

An excellent point, because the CWOP 'average' of "...the good, the bad, and the ugly..." pressures from the surrounding stations has always been suspect to me. When these surrounding stations are compared to my "reference" sites, some are WAY off (the ugly), and others (mostly Davis units) are slightly off (the bad). My "gold-plated" reference sites are: KTUS (NOAA @ Tucson Airport, 2546'), KDMA (USAF @ Davis-Monthan AFB, 2703'), and KRYN (Ryan Airfield, 2417')...and, when I see number consistency like this (small variation) for them, I know they're good:

KDMA, 2703' -- SLP = 985mb, ALT = 997mb
KTUS, 2546' -- SLP = 984mb, ALT = 998mb
KRYN, 2417' -- SLP = 983mb, ALT = 996mb

Sorry for my sophomoric lecture to a Phd candidate. I find that very few people in this forum that are bitchin' about CWOP vs Davis are , in fact, aware of differences. I will also defend myself concerning the "free" statement. I thought it was obvious I was talking about the CWOP service (which is becoming quite spotty, at least for me). Finally, I notice that the high-end weather stations still use serial connections which is the way Davis VP started. Also, I thought the latest Davis consoles had a SLP vs Alt. option, maybe I was wrong.

Oops, first, let me categorically state that I am NOT a trained weather person (but, I do do my homework). I am just a retired electronics engineer who, once upon a time long ago, flew as radar operator through typhoons in the Pacific with USN squadron, VW-1, "The Typhoon Trackers" -- hence, the knowledge of aviation weather terms. The Aerographers were the trained 'weather guessers', we (radar electronics) were the 'scope dopes.' My interest in weather stations began when I wanted to know how well (or not) our evaporative cooler was working. Weather is merely a tertiary hobby for me, so I sincerely appologize if I come across otherwise.

"In fact, my concern is centered upon the NOAA / NWS-TUC use and display of "my" weather data" -- I was not aware these people (NOAA / NWS-TUC) used data other than their own.

Don't know about all NOAA/NWS weather sites, but our local NWS-TUC has an "observations" page that simultaneously displays local CWOP/MesoWest/Mesonet/MADIS (but not WU) weather stations as well as their own (KTUS, KDMA, KRYN, etc.) data ( http://www.wrh.noaa.gov/mesowest/gmap.php?map=twc ). The ONLY reason I became involved with CWOP is to provide another citizens' "rain gauge" to help them (NOAA/NWS-KTUS and Tucson water) obtain more/better data on rain amounts and patterns, because the rain amounts reported at the airport do NOT truly represent how much totally fell nor where it fell.

[LFWX]

One option missing on the poll is to ignore CWOP quality ratings.

 This is how I look at it. Last summer I purchased an new VP2 console. Davis is a "reputable" company with calibration and it internal quality control systems in place. Using a GPS, I entered the altitude. Now using a local airport as a reference, my reading is with in 0.02 of what I would assume is more "professional" and regularly calibrated equipment (after all this is central KY where the one plane that lands per day relies on this equipment). So I am happy that my readings are as accurate as can be expected with the equipment in use. As Aardvark mentioned, change in the barometer reading is more useful than the actual reading it's self.

Now comparing your readings to the CWOP  is a little risky. Have you looked at the other stations that are close by? How "reputable" are these other stations? Are you comparing your readings with lesser calibrated equipment? Or are you one of the better calibrated stations helping to "clean up" a polluted data pool? Look at the bottom, of this page at some of the other stations in my control group. Currently there is variation from a positive 0.6 to a negative 1.8mb. I take CWOP's ratings with a grain of salt.

I AGREE

...and I would imagine the NWS is more interested our temperature, wind speed & rainfall data...the pressure data from airports should be more than enough in most parts of the country.