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Dew Point readings from data logger

swyman18
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Joined: Fri Apr 24, 2009 5:27 am
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Dew Point readings from data logger

Postby swyman18 » Thu Dec 30, 2010 7:40 pm

Hi Steve,

Just wanted to run something by you, not sure if this is a known issue or not. Did a search and didn't find anything, but may have missed it or didn't phrase my search terms properly.

I just recently started to use the data logger on my WS2315 to have Cumulus pull in data each time I start up my computer. If I have the "Calculate Dew Point" option checked, it appears to be writing the dew point to the log file as celsius instead of fahrenheit. If I uncheck the "Calculate Dew Point" option, it seems to write the dew point in fahrenheit, except it is a couple of degrees higher than the value from the console. When Cumulus is running, it stores the dew point correctly. So, basically, I can't get Cumulus to store a dew point value from the data logger that is in sync with what it stores when it is running. I can't tell if the console is just sending bad values from the data logger, or if Cumulus is doing something to the values before it stores it.

By the way, love the new Spike Removal facility in the new beta! I hope to be able to send another donation soon.

Thanks,

-Scott

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steve
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Re: Dew Point readings from data logger

Postby steve » Thu Dec 30, 2010 8:18 pm

swyman18 wrote:If I have the "Calculate Dew Point" option checked, it appears to be writing the dew point to the log file as celsius instead of fahrenheit.
Oops. Fixed in the next build.

If I uncheck the "Calculate Dew Point" option, it seems to write the dew point in fahrenheit, except it is a couple of degrees higher than the value from the console.
The logger doesn't actually store the dew point, so for logger data, Cumulus always calculates the dew point. I have two different bits of code, though, depending on whether the 'Calculate Dew Point' option is set or not. They should come up with the same answer (allowing for the above bug). Are you saying that when reading data from the logger, the Fahrenheit equivalent of the value it is writing in Celsius with the option selected is different to the Fahrenheit value it writes with the option not selected?
Steve
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swyman18
Posts: 61
Joined: Fri Apr 24, 2009 5:27 am
Weather Station: Davis Vantage Pro2
Operating System: Ubuntu Server 14.04
Location: Honoka'a, HI

Re: Dew Point readings from data logger

Postby swyman18 » Thu Dec 30, 2010 8:58 pm

Hi Steve,

OK, I did a couple of additional tests with the calc dew point option turned on and off by pulling data from the data logger, and here is what I've found:

Test #1 with Calc Dew Point turned ON:

Dew point at 10:35am HT according to console (and from log file in Heavy Weather) = 64.5 F
Dew point at 10:35am HT written to log file after opening Cumulus = 17.9 C

The conversion appears to be pretty close, so I think once that bug is fixed, that should take care of my problem.

Test #2 with Calc Dew Point turned Off:

Dew point at 10:45am HT according to console (and from log file in Heavy Weather) = 65.4 F
Dew point at 10:45am HT written to log file after opening Cumulus = 69.7 F

I'm not quite sure where the 69.7 F is coming from.

However, I think that bug fix should take care of my problem, as I prefer to keep Calc Dew Point turned on anyway.

Thanks!

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steve
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Re: Dew Point readings from data logger

Postby steve » Fri Dec 31, 2010 8:56 am

Thanks. It looks like my 'option off' code has an error. I'll check it.
Steve
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steve
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Re: Dew Point readings from data logger

Postby steve » Fri Dec 31, 2010 9:52 am

It seems that the formula I use in the 'option off' case does produce values a couple of degrees lower than the 'option on' formula, which is the formula I use elsewhere in Cumulus. I have no idea where the formula came from, but I'll change it so it's the same as the other case.

Thanks for taking the time to point this out.
Steve
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Hosting available for Cumulus web sites. See http://sandaysoft.com/forum/viewtopic.php?f=2&t=11876

Please read the posts in the Announcements section about the current status of Cumulus development since I have retired from my day job

swyman18
Posts: 61
Joined: Fri Apr 24, 2009 5:27 am
Weather Station: Davis Vantage Pro2
Operating System: Ubuntu Server 14.04
Location: Honoka'a, HI

Re: Dew Point readings from data logger

Postby swyman18 » Fri Dec 31, 2010 4:10 pm

No problem, thanks for researching.


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