Davis vue

[cfr301@gmail.com]

I hope this is a new topic didn't see any other on it.

We have a Davis vue up and running and works great with the software but...CWOP reporting is way off. Were using the altimeter setting. Both are the same in cumulus and on the console of 889 ft. We have the latest software. Rain gauge set to .01 in the .ini

We are set up identical to another station 20 miles away except of course for long/lat and elevation . Those are both correct and identical to what CWOP display says they should be.

My station is CWOP 7240. Or C7240.

We used a tweak to lower the barometer to the correct reading for CWOP but it through everything else way off such as PWS and weather underground.

CWOP is telling us it's the cumulus software we are out of ideas do you have any.

Rick Rohrbaugh

[steve]

CWOP requires 'altimeter' pressure rather than the MSLP that everyone else uses; MSLP is supplied by the station. The station uses various factors to calculate MSLP from the station pressure, but the altimeter pressure calculation just depends on altitude.

To calculate altimeter pressure, once a minute Cumulus reads the required data from the console (temperature, elevation etc) to allow it to reverse engineer the station pressure from the MSLP value, and from that it can then calculate altimeter pressure.

If your turn on the debug log, Cumulus will log to the debug.log file the data that it is getting from the station that it uses in the calculation, so you will then be able to see where it's getting the figure from.

[cfr301@gmail.com]

Absolute is coming back 29.07 which is what CWOP is seeing we are using the alt setting should we tweak the absolute? I am afraid doing that will throw the rest of the stuff way off?

[steve]

If CWOP is getting your absolute station pressure, unadjusted for your altitude, have you set your elevation correctly in the console? What do you mean by the 'alt setting'?

[steve]

Hold on - I think I see what you mean. You're using the altimeter setting on the console? Unfortunately this will send the Cumulus calculation off, as it doesn't know you're using that, and it affects the data that it receives.

[cfr301@gmail.com]

If we set the bar to Noaa it drops cwop only slightly other stuff doesnt change do you want us to put the wx console on altimeter or Noaa ?

[steve]

If NOAA is the same as the Vantage Pro2 setting (i.e. calculate MSLP using altitude, temperature, humidity etc) then that setting should make the altimeter pressure calculation work as it does on a VP2. I'm pretty sure that when this has come up before on the forum, changing to that setting has corrected the problem. If that doesn't help in your case, then I'm out of ideas without seeing those figures from the debug log that I mentioned.

Note that the MSLP calculation in the console is based on the historic values of some items, e.g. temperature, so perhaps the change in the setting takes some time to take effect.

[steve]

While you're getting me the debug.log file, can you please confirm that you haven't put any offsets on the Cumulus calibration screen for "Pressure" or "Davis Altitude"?

[glarsen]

Steve, another wierdness related to CWOP/APRS and altimeter pressure. On my station the pressure Cumulus delivers to APRS/CWOP via internet is significantly different that what is shown in the "wxnow.txt" file. Shouldn't they both be the same? For instance, right now wxnow.txt shows 1019.4 and the string sent to CWOP/APRS is 1016.7. If I enable WX transmission on my aprs station, the packets make it back to CWOP/APRS and cause a bad display of pressure. ie http://www.findu.com/cgi-bin/wxpage.cgi ... its=metric.

Thanks.
G

[steve]

Yes, the wxnow.txt file has MSLP in it, and it really should be Altimeter like CWOP. I'll fix that while I'm doing the other change.

[glarsen]

Post deleted.

[mdulrich]

We have a Davis vue up and running and works great with the software but...CWOP reporting is way off.

Steve, I wanted to let you know that I will be travelling down to the location of this weather station Friday afternoon to troubleshoot their setup and settings in the Vue and Cumulus. Hopefully I will see something that can correct the situation with CWOP. If not I will send you the debug file.

Mike

[mdulrich]

OK Steve I've check their setup, nothing seems abnormal.

Vantage Vue Console is set for NOAA barometer, elevation is correct and units are correctly set.

In Cumulus (with the 1097 version) station type is correctly set, elevation is correct and units are correct, calibration offset for barometer is zero.

Everything I can see is correct.

All sites are correctly receiving barometric pressure, except for CWOP who seems to be getting a pressure reading about 1" (about 30mb) too high.

I'm attaching the debug file.

I'm at a loss to what is whacky.

Mike

[steve]

The elevation used in the altimeter pressure calculation is 1778 feet, which is double the altitude stated above. Could you please confirm that the 'Davis Altitude' offset on the calibration setting screen is zero?

[mdulrich]

The elevation used in the altimeter pressure calculation is 1778 feet, which is double the altitude stated above. Could you please confirm that the 'Davis Altitude' offset on the calibration setting screen is zero?

Pressure Offset is 0.000 Davis Altitude is 889.000 in the Calibration screen

I've removed the Davis Altitude and set it to 0. It looks like in the debug file it is now reporting 889.

I don't know how I missed that.

CWOP likes the data much better

Mike