Mismatch Between Hardware and weeWX Data

[Dan Blanchard]

I've been running my weather station on weeWX for 2 days now after switching from a PC based solution for the past several years.  I noticed this problem after noticing that my station is no longer showing on the WeatherUnderground (WU) maps.  The data is still showing for my site on WU though (https://www.wunderground.com/dashboard/pws/KIDPOSTF43)

Everything has been going fine except I am currently having a problem with data inaccuracies.  All the data seems correct except the barometer reading.  The reading on my hardware is currently 30.30 and weeWX is showing 33.093 which is what is reporting to WU.

Can anyone please shed some light on this issue?  I've attached the syslog for reference.  Please let me know if there is anything else I can provide to help with this situation. If the solution requires changes in the configuration file, please be specific as I am still learning the Linux stuff.

Thanks,

Dan

Hardware: Lacrosse WS-2813

[gjr80]

Hi,

I suspect this is a case of comparing apples to oranges. WU wants to receive barometric pressure which is pressure corrected for altitude and pressure (and frequently humidity), but judging by the WeeWX Hardware Guide I suspect your station displays station or gauge pressure which is the raw absolute pressure. You can read about the three different pressures used by WeeWX in the wiki.

I can't comment on what your previous software did in terms of which of the pressures it sent to WU but perhaps it did not sent barometric pressure or perhaps I am wrong about what your station displays :)

Gary

[Dan Blanchard]

Thanks Gary, I think I understand what you are saying but the information going to WU is the same as my file at /var/www/html/weewx/index.html.  Does that change your answer?

[gjr80]

Slightly, but still apples and oranges. By default WeeWX displays barometric pressure so WeeWX and WU displaying the same 'pressure' is expected behaviour. The 'pressure' displayed by WeeWX can be changed with a simple change to a template, unfortunately what cannot be changed is what WU expects and (usually) what your station hardware displays.

Gary

[Dan Blanchard]

My station labels it as 'Pressure inHg' which is currently 30.30 and matches others in the area.  So I am a bit confused between what you said about barometric pressure vs. raw pressure.

Ultimately, is there a fix for me?  Can I make some kind of adjustment?

[gjr80]

On Monday, 10 February 2020 10:35:37 UTC+10, Dan Blanchard wrote:

My station labels it as 'Pressure inHg' which is currently 30.30 and matches others in the area.

I presume you mean the station display. The use of 'Pressure' is consistent with it being station pressure but it could mean anything, would not be the first time weather station hardware manufacturers have been vague, liberal with the truth or just wrong.

So I am a bit confused between what you said about barometric pressure vs. raw pressure.

Did you read the wiki article about the three different pressures that WeeWX uses? Could you explain what it is that confuses you?

 

Ultimately, is there a fix for me?  Can I make some kind of adjustment?

Not sure what you are trying to fix, if the issue is that you want everything to display the same value then sure there are changes you can make. Since you can't change what the station hardware displays you need to change what WeeWX and WU displays. Changing what WeeWX displays is easy, as I said its a simple change to a template. Changing what WU displays is more complex and involves changing the WeeWX WU uploader to upload WeeWX field pressure instead of field barometer. If you go down this path you need to accept a few things. Firstly, your WU data will be inaccurate (it expects barometric pressure and you will be sending it station pressure). Secondly, your changes to the template will be safe but your changes to the WU uploader will likely be overwritten each time you upgrade WeeWX.

I am not familiar with the WS-2813 so do not know if there is any ability to change what pressure it displays, I suspect there will not be a means though.

At the end of the day you might be displaying a different value to a lot of other folks, doesn't make them right and you wrong though.

Gary

[Dan Blanchard]

OK, let me absorb this information a bit and see what I can figure out.

[Les Niles]

33” is clearly too high for the barometric pressure. It is within spitting distance of what you would get if the pressure is corrected for your 2300’ elevation twice. Maybe the station is giving the corrected pressure but weewx is configured to think it’s the uncorrected pressure?

  -Les

On Feb 9, 2020, at 6:00 PM, Dan Blanchard <dan.z...@gmail.com> wrote:



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[Dan Blanchard]

Agreed.  If this is the case, can I configure weewx to show a different pressure?  If so, how do I do that?

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[gjr80]

Sorry, only use hPa here so the obvious nonsense inHg value was lost on me.

WeeWX is flexible enough that you change whatever you want to display on your web page, you can use another field or recalculate using whatever you like, it's just a case of altering the appropriate template. Similarly, you can change what is sent to WU, WeeWX is coded to send field barometer, to change that you need to dig into the code and your changes would likely not be safe across an upgrade.

In terms of solutions, one obvious check is that you have your station altitude set correctly in weewx.conf. You are after the altitude setting under [Station]. If altitude is set correctly then the solution is in the driver. The WS-2813 driver emits pressure and WeeWX calculates barometer and altitude. Have you run WeeWX directly to see what pressures are being include in loop packet and archive records. You should see all three pressures included as the data sent to console is after WeeWX has augmented the packet/record with whatever derived fields it can.

Unfortunately it looks like the WS-2813 driver cannot be run stand alone which would be handy to see exactly what data is coming from the driver (as opposed to running WeeWX directly which include driver and WeeWX calculated fields). You can driver only data by disabling the WeeWX StdWXCalculate service that calculates the additional fields. To disable StdWXCalculate edit weewx.conf and locate the process_services setting under [Engine] [[Services]]. It should look something like this:

process_services = weewx.engine.StdConvert, weewx.engine.StdCalibrate, weewx.engine.StdQC, weewx.wxservices.StdWXCalculate

just put a # in front of the StdWXCalculate service as follows:

process_services = weewx.engine.StdConvert, weewx.engine.StdCalibrate, weewx.engine.StdQC #, weewx.wxservices.StdWXCalculate

save and stop WeeWX if running and then run directly again. This time you should see no derived fields added and what you see should be coming from the driver. What pressure field is provide and if it is pressure is it indeed station pressure? If this is the case then the issue lies elsewhere, if not then the driver needs some scrutiny.

Gary

[Dan Blanchard]

I have confirmed and to the best of my knowledge, the station altitude is set correctly (altitude = 2320 foot).

When I run weewx directly (sudo weewxd weewx.conf) I get the following:

Traceback (most recent call last):

  File "/usr/bin/weewxd", line 64, in <module>

    weewx.engine.main(options, args)

  File "/usr/share/weewx/weewx/engine.py", line 852, in main

    sane = os.stat(config_path).st_ctime

OSError: [Errno 2] No such file or directory: '/home/pi/weewx.conf'

I really do not understand what that means.  I went and looked at line 64 and 852 but don't know enough to see a problem.  I understand the last line because my config file is at /etc/weewx/weewx.conf.  Is there another way to run it directly?

Once I get past this step, I can try the other suggestions you had.

[Les Niles]

The link in Gary’s mail explains how to run it — just give the full path to the config file as an argument to weewxd. Something like:

    sudo weewxd /etc/weewx/weewx.conf

  -Les

On Feb 11, 2020, at 9:21 AM, Dan Blanchard <dan.z...@gmail.com> wrote:



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[Dan Blanchard]

First of all, thanks for sticking with me on this.  I apologize for my denseness on this matter.  I am apparently not running the proper weewxd; I've tried sudo weewxd /etc/weewx/weewx.conf and get nothing. I do not know how to see what pressures are being include in loop packet and archive records. A little more remedial help is appreciated.  Thanks

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[gjr80]

What is nothing? Does it just return to the command prompt? Can you post a screenshot of the exact command entered and the entire response.

Gary

[Dan Blanchard]

Screen shot attached

[gjr80]

That is bizarre, but sudo weewxd weewx.conf still gives a reaction and error. Nothing appears in the log?

Gary

[Dan Blanchard]

I've attached the latest log and new screenshot

[gjr80]

OK, and what happens if you shutdown/kill all running instances of WeeWX.

Gary

[Dan Blanchard]

Do you mean sudo /etc/init.d/weewx stop

[gjr80]

Yes, that will shutdown a well behaved WeeWX service. Try that to start with.

Gary

[Dan Blanchard]

OK, I shut down via sudo /etc/init.d/weewx stop then I ran sudo weewxd /etc/weewx/weewx.conf and it is continuing to produce data.  I see that the barometer and altimeter are both the 32.xx readings while pressure is the same as what is reading on my station 29.9x.

Can I ge weewx to read the pressure reading in lieu of the barometer altimeter reading that it is presumably doing?

----

[gjr80]

On Wednesday, 12 February 2020 10:16:47 UTC+10, Dan Blanchard wrote:

OK, I shut down via sudo /etc/init.d/weewx stop then I ran sudo weewxd /etc/weewx/weewx.conf and it is continuing to produce data.  I see that the barometer and altimeter are both the 32.xx readings while pressure is the same as what is reading on my station 29.9x.

Hang on, let's go through this a bit more carefully. So you have run WeeWX directly and are seeing all three WeeWX pressure fields. WeeWX field pressure is matching what is on your console exactly. Fields altitude and barometer are 'in the 32s'. By my rough calculations an absolute pressure of 29.9inHg at 2300ft gives a barometer value of about 32.5. So on the face of it it would appear that the driver is providing data (whether it is right or wrong) in field pressure and WeeWX is calculating fields barometer and altimeter as expected.

Can I ge weewx to read the pressure reading in lieu of the barometer altimeter reading that it is presumably doing?

Now I don't understand. The 28xx driver takes the pressure value displayed on the station hardware and feeds that to WeeWX as the WeeWX field named pressure (after which WeeWX calculates fields barometer and altitude). Do you want the driver to instead take that pressure value displayed on the station hardware and feed that to WeeWX as the WeeWX field named barometer (after which WeeWX calculates fields pressure and altitude)? That can be done but it requires modification of the driver code, I would not being doing that lightly, someone did not roll a dice and randomly decide to put the pressure value from the 2813 in field pressure, it was done for a reason.

I was looking for a 2813 manual and the only manual I could find was for a WS-2813U-IT weather station. On page 14 it talks about setting a 'Relative value pressure reference setting' based on a value from a weather service, airport etc. Is that your station and have you set that correctly or if not your station is there a similar setting?

Gary

[Dan Blanchard]

The further I go, the more complex it is getting.  First, yes I have a WS-2813U-IT and yes, I did set the relative pressure to match the local weather service.

I don't want to muddy the waters any more, but how is it that I stopped the wewx service but it is still reporting?  I'm still trying to understand this thing.

[gjr80]

sudo /etc/init.d/weewx stop will stop the current running service but if you have other instances running, for example WeeWX directly, sudo /etc/init.d/weewx stop will have no effect as WeeWX is not running as a service. When running WeeWX directly you need to stop the execution using a control key sequence (CTL-C) or list the running WeeWX processes with ps -aux|grep weewx and then use the Linux kill command to kill the process.

Whenever you do a lot of stop-starting, running services/running directly and odd things (apart from odd pressure values :) ) are happening it can be because there is more than one instance of WeeWX running. If you look at the log you can usually see it by there being more than one process ID number against WeeWX at any one time.

Well if your relative pressure is set correctly I am out of ideas on how to fix this. I am not convinced the driver is wrong but I guess it is possible. Really need someone who understands the driver operation and the 2813 to take that further.

Gary

[Andrew Milner]

check that the absolute pressure is correct - I have had a FO station which had a dodgy pressure sensor before now.  Calibrating pressure in weewx solved it.

[Dan Blanchard]

Andrew, how do I calibrate the pressure in weewx? Also, what's a FO station?

[Andrew Milner]

1. use stdcalibrate section of weewx.conf

http://weewx.com/docs/usersguide.htm#StdCalibrate

2. FO station = Fine Offset weather station

[Dan Blanchard]

Andrew, are you suggesting that I make a 'correction' entry under [StdCalibrate] such as barometer = barometer -2.8  assuming that I am getting a pressure reading of 30.13  and Barometer and ALtitude readings of 32.93?

(see attached screenshot)

[Andrew Milner]

If you have a LaCrosse WS28xx station then according to the hardware guide the station outputs PRESSURE in weewx terminology - regardless of what LaCrosse call it - and weewx should calculate barometer and altimeter settings.

If pressure is incorrect then it can be adjusted as you specified - by adjusting pressure (not barometer or altimeter)

Make sure pressure is set to use hardware and barometer and altimeter are set to use software.

I am surprised barometer and altimeter are the same values - have you set the station's altitude in weewx.conf, and have you specified software generation for the values?

[Dan Blanchard]

Hey Andrew, will you please look at the attached screen shots and let me know if this looks correct?

Do I need to restart (sudo /etc/init.d/weewx restart) after I make these changes?  I have and the changes don't seem to be taking effect.  Is there something else I need to do?

With regard to the barometer and altimeter having the same settings; I have probably misled.  They are not exactly the same but they were relatively close to each other compared to the pressure value.  Here are the current readings as of now when I run sudo weewxd /etc/weewx/weewx.conf.

pressure: 29.98

altimeter: 32.57

barometer: 32.74

[Kevin Davis]

Do you need a space between your minus sign and the adjustment value?

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[Dan Blanchard]

I don't know, but that makes sense so I did it.  I'm still not getting desired results though.

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[Andrew Milner]

I give up - looks correct to me.

have you run from the command line and seen the LOOP and REC data weewx is receiving?

what altitude is your station, and what values are you currently getting for pressure, barometer and altimeter?  

[Dan Blanchard]

Altitude is 2,320 ft. and the values are in the screen shot on the previous post.  Did you see that?

[Andrew Milner]

I am  not sure I understand what you think is wrong with the readings of

Pressure 29.89

Barometer 32.609

Altimeter 32.40
and why you believe something is wrong

[Dan Blanchard]

Andrew, that's a good questions; let me clarify.  

This issue started when Weather Underground (WU) stopped showing my station on the maps. I found out that was because I was reporting an incorrect barometric 'pressure.'  As I dug into the details I found that my station was displaying the correct pressure (29.xx) but by the time it got to WU, it was displaying the barometer reading (32.xx) from weewx.  This can also be demonstrated by looking at the data displayed at /var/www/html/weewx/index.html (see attachment) so I assume that weewx is taking the pressure from my station and somehow converting it or exchanging it for barometric pressure before it gets uploaded to WU.  I just want the pressure from my unit to be what is reported to WU.

Side note: I've been running this station for many years on a Windows based system and it has been working fine.  So I know the hardware side is working; just something different about how weewx reports pressure (or barometer, or altimiter).

Does that help clarify my issue?

[Andrew Milner]

I would expet you to be reporting barometer = sea level pressure which is pressure adjusted for temperature and altitudebecause weather stations always report sea level pressures.

Is what you call 'correct' pressure the raw pressure of the instrument or a pressure which you have set.  Does the station output the raw pressure or the manually adjusted pressure in the loop records?

[Dan Blanchard]

It is likely that I am mis-using the terms altimeter, barometer, and pressure.  I'll clarify what I mean here.  

What I previously defined as 'correct' pressure is that the pressure reported by my station (LaCrosse WS-2813U-IT) matches the National Weather Service barometer reading (https://forecast.weather.gov/MapClick.php?lat=47.715130000000045&lon=-116.94667999999996#.XkdkXDFKiUk). For example, right now my station is reading 30.06 pressure and the NWS site is reporting 30.0 barometer.  Ultimately I just want my WS-2813 pressure reading to match the WU pressure reading (https://www.wunderground.com/dashboard/pws/KIDPOSTF43).  Right now it appears that WU is reading the weewx barometer reading.  Is there a way to have weewx report the pressure reading to WU?

My WS-2813 outputs the manually adjusted pressure in the Loop records (see attachment).  I don't see a way to change that.  Here is a link to the manual (https://www.lacrossetechnology.com/media/catalog/product/w/s/ws-2813u-it.pdf).

On Friday, February 14, 2020 at 9:22:17 AM UTC-8, Andrew Milner wrote:

I would expect you to be reporting barometer = sea level pressure which is pressure adjusted for temperature and altitude because weather stations always report sea level pressures.

[Les Niles]

OK… The “pressure” that your station is displaying is what it should be displaying: the ambient air pressure, correct for your altitude.  In weewx, this is called “barometer” because that is what weather stations report for barometric pressure.  “Altimeter” is basically the same thing; there are differences in exactly how it is corrected, but those differences are minor and can be ignored for now.  The distinction between what weewx calls “barometer” and “pressure” is important, though, for anyone more than a few hundred feet above sea level.  

From the manual, it appears that the WS-2813 uses a simple method for correcting to sea level, by allowing the user to adjust a correction factor that is applied to the actual measured pressure until the reading matches some local reference barometric pressure report.  This automatically also corrects for any errors in the pressure sensor itself, a handy bonus. There’s not reference in the manual to any other kind of pressure being reported, so it only makes sense that what it transmits via the USB interface is also this corrected pressure, i.e., “barometer.”  But the WS28XX driver documentation, and as far as I can tell the code also, assume that the pressure reading fro the hardware is what weewx calls “pressure,” that is, the actual ambient pressure before correction for altitude.  As far as I can tell, all of the WS28XX LaCrosse stations work the same way as yours and actually send the corrected barometer reading. Maybe because the LaCrosse documentation calls it “pressure,” it was mistakenly interpreted as raw pressure reading in the driver. 

The bottom line is, I’m pretty sure the issue is that the driver is wrong.  I’m not familiar enough with that part of the weewx code to offer a fix, but it should be pretty simple for someone who is familiar with that code.  

  -Les

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[Andrew Milner]

if indeed, and i now tend to agree, the station displays and outputs a manually adjusted barometer which is set to a sea level reading from local weather stations and not pressure then barometer should be set to hardware and pressure and altimeter set to software, and not as i previously suggested.

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[gjr80]

As this thread has drawn on I agree the solution is in the driver. I found it had to believe that a driver could have been around for so long with an incorrect 'pressure' being used and the issue never having come up before. Sure enough, this thread from 2016 bears a remarkable similarity to the issue here. It also seems that Tom acknowledged that the WS2813 actually outputs altimeter not pressure as coded in the driver. Later in the thread there are suggested changes to the driver but it gets a bit murky around some corrections that are being applied within StdCaibrate. Seems no changes were ever made to the driver though. Might be worthwhile for Tom or Matthew to revisit this.

Gary

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[Thomas Keffer]

This is Matthew's baby. Matthew?

-tk

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[Dan Blanchard]

Andrew, I've set barometer = hardware and altimeter = software and pressure = software.  I've restarted weewx, but nothing has changed in the Loop.

[Dan Blanchard]

I don't know who Matthew is, but I am eagerly awaiting his input.  Thanks.

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[Andrew Milner]

pressure, barometer and altimeter look reasonable to me.  why are they wrong?

[gjr80]

Andrew,

I know Wikipedia has its issues but when you consider the pressures posted here and this I think it is pretty clear there is an issue with the OPs pressures.

Gary

[Les Niles]

Setting those that way won’t fix the problem.  Those settings are hints to weewx about what to use when the weather station hardware provides multiple values.  The WS28XX driver is hard-coded to interpret the data from the station as weewx “pressure,” and that is the only pressure-related datum sent by the WS28XX stations.  

  -Les

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[Andrew Milner]

well if it is hard coded for pressure then the station adjustment made by the OP should be to set his station to a known sea level pressure and subtract a correction for altitude (2.6 for 2300 ft I think) and all should then be ok

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[Les Niles]

That would work, other than having the station console reading uncorrected pressure.

Or, the OP could just move to some place at sea level. :)

  -Les

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[Dan Blanchard]

OK guys, thanks for all the help on this.  Jerry, I assume that the info below is in the driver for my WS-28xx and if that is the case, where is that driver located?  

Next, I want to clarify something... I have used the calculator at http://www.csgnetwork.com/barcorrecthcalc.html to set my altitude (2,320 ft.) and an observed pressure of 30.16 inHg as reported for my area (https://tinyurl.com/yx65ckcm).  This gives me an adjustment of -2.43 so I have set my station pressure to 27.73 inHg. This is now reporting 30.35 inHg barometer reading at Weather Underground (WU).  Although this is working, I feel as if it a work-around but maybe it is just a limitation of my station?  Thoughts...

On Sunday, February 16, 2020 at 9:44:46 PM UTC-8, J D wrote:

Hi,

I am using the ws23xx driver on ws2316 hardware and this driver sends absolute pressure to weewx in the packet as "pressure" ..

The ws28xx hardware sends relative pressure and the ws28xx driver also sends the reading to weewx in the packet as pressure. See below

packet['pressure']    = get_datum_diff(data._PressureRelative_hPa,

                                               CWeatherTraits.PressureNP(),

                                               CWeatherTraits.PressureOFL())

I suspect the code should read.

packet['barometer']    = get_datum_diff(data._PressureRelative_hPa,

                                               CWeatherTraits.PressureNP(),

                                               CWeatherTraits.PressureOFL())

Or you could just change the altitude of the station as Andrew suggest.

Jerry

On Sunday, February 9, 2020 at 4:36:51 PM UTC-7, Dan Blanchard wrote:

I've been running my weather station on weeWX for 2 days now after switching from a PC based solution for the past several years.  I noticed this problem after noticing that my station is no longer showing on the WeatherUnderground (WU) maps.  The data is still showing for my site on WU though (https://www.wunderground.com/dashboard/pws/KIDPOSTF43)

Everything has been going fine except I am currently having a problem with data inaccuracies.  All the data seems correct except the barometer reading.  The reading on my hardware is currently 30.30 and weeWX is showing 33.093 which is what is reporting to WU.

Can anyone please shed some light on this issue?  I've attached the syslog for reference.  Please let me know if there is anything else I can provide to help with this situation. If the solution requires changes in the configuration file, please be specific as I am still learning the Linux stuff.

Thanks,

Dan

Hardware: Lacrosse WS-2813

[Dan Blanchard]

Where did you all go?  I was hoping for some comments on my last post.  Does everything I state seem correct?

[Les Niles]

I thought your questions were answered: what you’ve done is a workaround. Fundamentally, it’s not a limitation of the LaCrosse hardware, it’s a bug in the driver.  

  -Les

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[Dan Blanchard]

I was under the impression that what JD wrote was a change I can make to the driver.  If so, how can I access the driver to modify it?

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[Les Niles]

JD said that he “suspects” that would be the right change.  It would help if you tested it, but be prepared for it not to work or break the driver.  Save the original version of the file, and restart weewx after changing it in order to load the new version.

The location of the driver can depend on the type of OS and how you installed weewx.  On my raspberry pi, it is /usr/share/weewx/weewx/drivers/ws28xx.py.

  -Les

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[Dan Blanchard]

Thanks Les, I will give this a go.  Will be a couple days though before I can get to it.  I'll report my findings.

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[mwall]

dan,

it is quite possible that the driver is coded incorrectly.  luc and i did the development and testing of the ws28xx driver, and all three locations were within 200 feet of sea level.  so it is quite possible that the device reports barometer, not pressure.  (if the device reports barometer, then it must have some way for a user to calibrate it, and i do not recall whether that is an explicit altitude or if it is an adjustment to the sensor output)

anyway, just change 'pressure' to 'barometer' in the driver, then restart weewx.  there are two places where this happens - one for loop data, one for historical data.

for loop data, change this:

        packet['pressure']    = get_datum_diff(data._PressureRelative_hPa,

to this:

        packet['barometer']    = get_datum_diff(data._PressureRelative_hPa,

for historical data, change this:

'pressure': self.PressureRelative,

to this:

'barometer': self.PressureRelative,

[mwall]

and now i see that JD made the same suggestion.  apologies for being late to the party.  i'm working my way through 300 weewx emails...