Max wind gust

[ilan72]

sorry if i am repeating someone else's question. i tried to find an answer here ..

i have a VANTAGE VUE weather station. sometimes i see that the max wind gust for the day shown in Cumulus is a bit different than the one recorded in the Davis console.The time of the max point, however, is the same.

what can be the reason? do i have to change anything in my Cumulus settings so i will get the same results?


thanks!

[steve]

Yes, this gets asked a lot, I should really do a FAQ.

Cumulus can never guarantee to catch every reading from the station, because it relies on the Davis DLL to fetch the data, and even though Cumulus polls the DLL quickly enough, sometimes it takes the DLL a little bit too long to fetch the data, so a reading is missed. You can watch the 'last data read' time in the bottom right hand corner to see how often it's getting the data; the wind data updates every 2 to 3 seconds or so (it may be 2.5 seconds?) so if you see that Cumulus quite often doesn't get the data that often it may be missing readings. It's the average time that you need to watch, over a period of time it needs to be about 2 to 3 seconds between each reading.

I've noticed that the DLL takes a long time to read the pressure data that Cumulus reads once a minute, which Cumulus uses to calculate Altimeter Pressure for CWOP. I should really make that an option for people who don't upload to CWOP and don't want the altimeter pressure for other reasons. I did change the code and that seemed to make it work quicker, but I can't remember what build that was in (and you haven't said what build you're using anyway). But in any case, I've just checked mine, and it still seems to be taking 5-10 seconds to do it (it does it on the minute) unfortunately. At some point I need to try the latest Davis DLL to see if they've improved things.

The only other thing to check is in cumulus.ini; if you have a VP2SleepInterval setting, make sure it's zero.

[neondesertweather]

I've noticed that the DLL takes a long time to read the pressure data that Cumulus reads once a minute, which Cumulus uses to calculate Altimeter Pressure for CWOP. I should really make that an option for people who don't upload to CWOP and don't want the altimeter pressure for other reasons. I did change the code and that seemed to make it work quicker, but I can't remember what build that was in (and you haven't said what build you're using anyway). But in any case, I've just checked mine, and it still seems to be taking 5-10 seconds to do it (it does it on the minute) unfortunately. At some point I need to try the latest Davis DLL to see if they've improved things.

Steve, I'm running v1.9.3 Build 1034 and it takes about 8 seconds (on the minute) to update and 2 seconds otherwise. About 2 days ago I noticed Cumulus recorded a high gust of 17mph, when in
reality it was 21mph. I am not using Cumulus to upload to CWOP and I like your idea of making the calculation of Altimeter Pressure option if this would reduce some of the missed high gusts.
Would this change require that a formal enhancement request be made?

The only other thing to check is in cumulus.ini; if you have a VP2SleepInterval setting, make sure it's zero.

Should those of us running VirtualVP still be using a VP2SleepInterval setting of 1100?

[steve]

I am not using Cumulus to upload to CWOP and I like your idea of making the calculation of Altimeter Pressure option if this would reduce some of the missed high gusts.
Would this change require that a formal enhancement request be made?

No, I'll just add it as an ini-file option along with the changes I'm making at the moment.

Should those of us running VirtualVP still be using a VP2SleepInterval setting of 1100?

You need to be using something higher than zero, yes, otherwise Cumulus will sit in a tight loop using 100% CPU. If you're getting updates at around 2 second intervals then it sounds like it's a reasonable setting, and you shouldn't miss any readings (assuming Virtual VP doesn't miss them in the first place). It's interesting that there is still a delay reading the barometer data even when using Virtual VP; it must not have the data to hand and has to read it from the console.

[neondesertweather]

I am not using Cumulus to upload to CWOP and I like your idea of making the calculation of Altimeter Pressure option if this would reduce some of the missed high gusts.
Would this change require that a formal enhancement request be made?

No, I'll just add it as an ini-file option along with the changes I'm making at the moment.

Excellent. I'll watch for the change and let you know if it seems to make a difference.

[ilan72]

thanks for your reply! it's , anyway, not so crucial, normaly i get the same max point in the console and in cumulus and when it's not the same the difference is really minor. For exact statistical purposes i can always use the NOAA report.
i am using the latest version of Cumulus.

[steve]

I've noticed that getting the reception stats (which is also done on the minute) also takes three seconds. Perhaps it shouldn't read them so often, maybe every 15 minutes or so?

[neondesertweather]

I've noticed that getting the reception stats (which is also done on the minute) also takes three seconds. Perhaps it shouldn't read them so often, maybe every 15 minutes or so?

Agreed. Unless you're trying to diagnose a reception issue, once every 15-30 minutes is probably all that's really necessary.