wind chill for Vantage Pro 2

[brisguy foo]

Hello all,

I have been using weewx (3.9.2.1 with standard skin) successfully for several months now and just noticed that the wind chill graph does not reflect the values reported by my VP2. It always matches the outside temp values. I have seen that weewx can calculate wind chill on its own, but since the VP2 provides this data, I was expecting weewx to use it. Does it?

Thanks

[Tom Keffer]

The service StdWXCalculate sets where wind chill (and other derived types) comes from. If you set it to "prefer_hardware", it should come from the VP2, if it's available. 

Also, please note that wind chill does not kick in unless the wind is over 3 mph, and the temperature is below 50F.

The online documentation is for V4.1, but the semantics are the same for your version. See the section [[Calculations]].

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[brisguy foo]

Thanks for the reply. I did check the weewx.conf file and and found that wind chill should be coming from the VP2. See below. I believe your comment about when wind chill applies is only for the case where weewx calculates the result. The VP2 does not have the restriction of being below 50deg. Note that if I use the software supplied by Davis (WeatherLink), it will display the wind chill data that matches what is displayed on the console. Is there something else I may be missing?

[StdWXCalculate]
   
    [[Calculations]]
        # How to calculate derived quantities.  Possible values are:
        #  hardware        - use the value provided by hardware
        #  software        - use the value calculated by weewx
        #  prefer_hardware - use value provide by hardware if available,
        #                      otherwise use value calculated by weewx
       
        pressure = prefer_hardware
        barometer = prefer_hardware
        altimeter = prefer_hardware
        windchill = prefer_hardware
        heatindex = prefer_hardware
        dewpoint = prefer_hardware
        inDewpoint = prefer_hardware
        rainRate = prefer_hardware

[Tom Keffer]

Davis has a publication Calculations of Derived Variables, that shows the formula they use. It's the same formula used by WeeWX. From the publication, it appears that they do not apply the 3 mph and 50F limits. Nevertheless, if you go to the NOAA source, those restrictions do apply. So, we apply them when calculating windchill in software.

But, that's not your question. 

The VP2 emits windchill only in its LOOP packets, not the archive records coming off the logger. So, when it comes time to put something in the database, WeeWX has to synthesize something. By default, it uses the average windchill seen during the archive interval. This is why you see something different from what is on the console. So, it's coming from hardware, just not the way you think it does.

Alternatively, you can have WeeWX save only the last value seen in the archive interval by adding the following to weewx.conf:

[Accumulator]

  [[windchill]]

    extractor = last

That may bring it closer to what you're seeing on the console.

-tk

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[Tom Keffer]

Geez, Gary, you're right! So, you would also have to specify LOOP2 packets. See the section [Vantage] in the User's Guide.

[Vantage]

  loop_request = 2

-tk

On Fri, Jul 24, 2020 at 5:13 PM gjr80 <gjrod...@gmail.com> wrote:

Windchill is only in included in the Davis LOOP2 packet, it’s not in the LOOP packet or archive record (the defaults) from the console. So unless you have set WeeWX to use the LOOP2 packet WeeWX will never see windchill from the console, irrespective of StdWXCalculate settings.

Gary

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[gjr80]

Ha, shouldn’t have been in such a rush and should have read your reply thoroughly, thought I was repeating what you had said. But yes LOOP2 only, some gems in there but nothing that has convinced me to change.

Gary

[brisguy foo]

Thanks for the replies guys!

I did update my conf file as suggested, however I am confused by the comment that wind chill "is not in the LOOP or archive record from the console".

I know I was able to see wind chill in historical data downloaded from the console logger and displayed using WeatherLink. If you are referring to the weewx archive, then I am concerned that the not all LOOP 2 data is being stored.

Please help me understand if you don't mind. I should be able to see the result in a few days anyway, but I'd like to know how this works.

Thanks!

On Friday, July 24, 2020 at 5:21:48 PM UTC-7, Tom Keffer wrote:

Geez, Gary, you're right! So, you would also have to specify LOOP2 packets. See the section [Vantage] in the User's Guide.

[Vantage]

  loop_request = 2

-tk

On Fri, Jul 24, 2020 at 5:13 PM gjr80 <gjrod...@gmail.com> wrote:

Windchill is only in included in the Davis LOOP2 packet, it’s not in the LOOP packet or archive record (the defaults) from the console. So unless you have set WeeWX to use the LOOP2 packet WeeWX will never see windchill from the console, irrespective of StdWXCalculate settings.

Gary

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[Tom Keffer]

I think Gary was referring to "LOOP" packets as opposed to "LOOP2" packets. They are two different kinds of packets the Vantage series is capable of emitting. Only the latter, LOOP2, has windchill.

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[brisguy foo]

UPDATE:

Changed by weewx,conf file to read:

[Vantage]

...

# Use LOOP2 data in order to get access to wind_chill
    loop_request = 2

Restarted weewx

After only an hour or so, I saw that my console was reporting wind-chill that was 2 to 3 degrees lower than outside temp, but the weewx graph showed no difference.

Checked the syslog file today, and at the time of the restart found the following odd statement:

16:40:18 raspberrypi weewx[30378]: wxcalculate: The following values will be calculated: barometer=prefer_hardware, windchill=prefer_hardware, dewpoint=prefer_hardware, appTemp=prefer_hardware, rainRate=prefer_hardware, windrun=prefer_hardware, heatindex=prefer_hardware, maxSolarRad=prefer_hardware, humidex=prefer_hardware, pressure=prefer_hardware, inDewpoint=prefer_hardware, ET=prefer_hardware, altimeter=prefer_hardware, cloudbase=prefer_hardware

It seems odd that weewx would report it is calculating values that have been set to 'prefer_hardware', plus I only used that for five parameters, and weewx is reporting it has been set for several more.

So now I have two issues:

1. How can I tell whether LOOP2 packets ate being used (the graph indicates they are not)

2. Why is weewx reporting it is calculating values that have been set to 'prefer_hardware'?

Thanks,  Stan

[gjr80]

On Wednesday, 29 July 2020 10:00:01 UTC+10, brisguy foo wrote:

UPDATE:

Changed by weewx,conf file to read:

[Vantage]

...

# Use LOOP2 data in order to get access to wind_chill
    loop_request = 2

Restarted weewx

After only an hour or so, I saw that my console was reporting wind-chill that was 2 to 3 degrees lower than outside temp, but the weewx graph showed no difference.

Using the plots to check what is happening can give misleading results; not saying that is the case here but some plots are not generated every cycle and there can be caching issues. Best evidence is to look at what is in the database or loop packets/archive records or look at the database.

 

Checked the syslog file today, and at the time of the restart found the following odd statement:

16:40:18 raspberrypi weewx[30378]: wxcalculate: The following values will be calculated: barometer=prefer_hardware, windchill=prefer_hardware, dewpoint=prefer_hardware, appTemp=prefer_hardware, rainRate=prefer_hardware, windrun=prefer_hardware, heatindex=prefer_hardware, maxSolarRad=prefer_hardware, humidex=prefer_hardware, pressure=prefer_hardware, inDewpoint=prefer_hardware, ET=prefer_hardware, altimeter=prefer_hardware, cloudbase=prefer_hardware

It seems odd that weewx would report it is calculating values that have been set to 'prefer_hardware', plus I only used that for five parameters, and weewx is reporting it has been set for several more.

So now I have two issues:

1. How can I tell whether LOOP2 packets ate being used (the graph indicates they are not)

There is no direct way that I know of. I would stop WeeWX and then run it directly so you see the loop packets and archive records on the console. What do you see in the loop packets (lines starting with LOOP:) and archive records (lines starting REC:) on the console? How does windchill compare to outTemp? If you are seeing THSW in the loop packets then WeeWX is receiving the LOOP2 format loop packet, if THSW is not there then I suspect you are still using the LOOP format loop packets.

 

2. Why is weewx reporting it is calculating values that have been set to 'prefer_hardware'?

If WeeWX is calculating windchill it is most likely because windchill is not being received by WeeWX. Change 'prefer_hardware' to 'hardware' for windchill and restart/reload WeeWX. If windchill disappears it will be because WeeWX is not receiving windchill which implies you are still using LOOP format loop packets.

@tkeffer. Tom, I see the vantage driver does not log what format loop packet is being used, perhaps it should?

Gary

[Tom Keffer]

@tkeffer. Tom, I see the vantage driver does not log what format loop packet is being used, perhaps it should?

I was just thinking the same. Commit bb12695.

-tk

[brisguy foo]

OK, I tried stopping the daemon and running directly. The LOOP data shows no difference between outTemp and windchill although the console shows a 4 degree difference. I have attached my conf file in case I messed up something. I see that when the change to support LOOP2 was submitted, a request was made for testers. Was it ever tested?

On a side note, when I tried running weewx directly without a config file argument, it would not run, even though my config file is located at /etc/weewx/weewx.conf. Is that a bug?

Thanks!

[Tom Keffer]

On a side note, when I tried running weewx directly without a config file argument, it would not run, even though my config file is located at /etc/weewx/weewx.conf. Is that a bug?

No, but it suggests that you may not be editing the weewx.conf file that weewxd is actually using.

At this point, I have to ask for a log. Restart weewx, let it run through the first reporting cycle. Post the resultant log.

-tk

[brisguy foo]

I suppose that is possible, but remember, I started the program directly, using the /etc/weewx/weewx.conf as the conf file. That is the file I sent to this thread.

Here is the syslog file. Sorry, it is a bit busy since I found that the daemon did not restart yesterday when I thought it did (still don't know why - no error message and the terminal indicated success) and would not start from the command line today so when I ran it directly again, there were lots of records to catch up.

[Tom Keffer]

Found the problem. You're using V3.9.2, but support for the LOOP2 format was not introduced until V4.0.0. You'll need to upgrade to do this.

I was misled because the change log (wrongly) said that support for LOOP2 packets was introduced in V3.7.0, so I assumed support was there --- I never bothered to check the actual code base. The log was fixed in commit 56ebe96

Sorry for the confusion.

-tk

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[brisguy foo]

I was about to for that anyway. However, now that I am ready, I am not sure how to proceed. I see some info on installing and some on removing but none on upgrading. Do I need to uninstall first? Or is there an apt-get upgrade command?

Thanks again.

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[Tom Keffer]

See the Upgrade Guide. http://www.weewx.com/docs/upgrading.htm

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[brisguy foo]

Ah, thanks for that. Should have been able to figure that out myself. 

However, I just tried to upgrade using these commands:

sudo apt-get upgrade

sudo apt-get install weewx

And was informed that 3.9.2 is the latest version!

Does this mean I have to download the .tar and do it manually? I'm not too confident I can pull that off...

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[Kevin Davis]

Do an “apt-get update” first to update the package manager so it’s aware of the newest version numbers. 

On Jul 30, 2020, at 6:04 PM, brisguy foo <iams...@gmail.com> wrote:



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[brisguy foo]

Sorry, that was a typo. I did run apt-get update (not upgrade). It seemed to run successfully but I just now noticed the following:

E: Repository 'http://weewx.com/apt squeeze InRelease' changed its 'Origin' value from '. squeeze' to 'python2 squeeze'
E: Repository 'http://weewx.com/apt squeeze InRelease' changed its 'Label' value from '. squeeze' to 'python2 squeeze'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.

Turns out there was an error when I tried to do the update. I got around this by rerunning the commands to trust weewx repository and configure python 3. Did not do this before because the user's guide says you only need to do it once upon first install.

Anyway, during the weewx install it told me it was going to replace skins.conf and allowed me the D option to see the differences, but I could not figure out how to get out of it. After trying several things, I used CTL-Z which stopped the install process (I knew I would screw it up !). Tried running install afterwards, but it won't run - saying the process is locked.

E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?

Is there any was to recover from this?

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[Graham Eddy]

ctl-Z stop just means you have paused the command and placed it in background - it is still there, waiting, but paused (and holding the lock). bring it back to foreground to resume and interact with it by      $ fg      

then kill it with ctl-C

(or use some other method to kill it gently such as    $ kill %1    )

then try the command again.

cheers

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[brisguy foo]

Thanks Graham. I read that killing the install process will mess up the install at a minimum and possibly corrupt the system. Is there a way to get back to the install script from the D option?

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[Praveen Chandrasekaran]

I see an issue where graph doesn't match the lowest wind chill in stats. That's because of averaging?

[Andrew Milner]

probably. Try and plot min wind chill instead of avg and for heat index plot max and you may get what you expect.

[Praveen Chandrasekaran]

And how do I do that?

[Andrew Milner]

set aggregate_type in the appropriate graph section(s) of skin.conf

[Praveen Chandrasekaran]

That didnt help. I dont see the min windchill i see in stats in 5min archive records either. 

I think since I set record_augmentation to true, it picked high/low from loop packet. But since archive packets dont have windchill, the 5 min records have the average.

I see this above:

[Accumulator]

  [[windchill]]

    extractor = last

However this would only make it take last value and put in db. IS there a way to put 5 min min/max into the archives?

[Praveen Chandrasekaran]

https://github.com/weewx/weewx/wiki/Accumulators

Ok this has some info. I think this is what I need to do.

Need to set extractor to max/min