Topic: Moved Davis VP2 Station and need to calibrate barometer

[lightmaster]

It's been at least 5 years since I've had to bother with calibrating pressure and I don't remember how to do it. I cleared all the data on the VP2 console after moving to a new location, so its essentially a new station, and currently the barometer is set to what the KBHC airport's barometer is. It is 3 miles from my house and both are conveniently located within a foot of each other above sea level (200ft and 201ft).

What do I need to do to get it ready to report to CWOP and other sites?

[CW2274]

If you're comparing SLP to SLP, nothing. Just try to have the height of your console within ten feet or so and SLP selected. If you're comparing your SLP to the altimeter, that's a different story.

[gszlag]

It's been at least 5 years since I've had to bother with calibrating pressure and I don't remember how to do it. I cleared all the data on the VP2 console after moving to a new location, so its essentially a new station, and currently the barometer is set to what the KBHC airport's barometer is. It is 3 miles from my house and both are conveniently located within a foot of each other above sea level (200ft and 201ft).

What do I need to do to get it ready to report to CWOP and other sites?

Although I don't own a Davis weather station the advice is the same for all weather stations.
If you are at the same elevation as the reference calibrated barometer (KBHC) then set your station pressure to be the same. Done.

Station pressure (mesowest calls this "Pressure") can be found here:
https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?stn=KBHC

Once you match KBHC station pressure, you should be matching KAMG SLP (a little further away) on your console.

Since CWOP is expecting Altimeter, you would need to use some other hardware device or software to translate station pressure to Altimeter.

Or alternatively, if you are using the original VP2 console, you will need to forget about SLP and set your elevation to zero and calibrate your console to match KBHC Altimeter. This method would be close but not quite as accurate.

[lightmaster]

What do you mean by "original VP2 Console"?

And I guess I'm more asking does the VP2 console use altimeter or SLP? If it makes a difference,  it's product number 6312.

[gszlag]

What do you mean by "original VP2 Console"?

And I guess I'm more asking does the VP2 console use altimeter or SLP? If it makes a difference,  it's product number 6312.

..the original console meaning the one that came with your kit when you bought it. Some Davis owners upgrade to the Vantage Vue console as that particular model calculates SLP and Altimeter.
..you might want to check out this thread and note CW2274's answer regarding consoles: https://www.wxforum.net/index.php?topic=43164.msg447301#msg447301

[lightmaster]

Will probably end up getting a Vue console later on then. According to https://www.manula.com/manuals/pws/davis-kb/1/en/topic/barometric-pressure-issues, VP2 console uses "standard method" of averaging 12 hours of temperature to calculate the SLP. The actual manual for the VP2 Console says "*Barometric pressure readings are standardized to sea level."

[gszlag]

... the VP2 Console says "*Barometric pressure readings are standardized to sea level."

..not a bad explanation but we need to expand it (Altimeter or SLP) a bit more:

"..represents what the atmospheric pressure would indicate if your station was theoretically located at sea level. This is done because it provides a common barometric reference for all weather stations regardless of their elevation."

[TomD]

I'm assuming you need to know how to adjust the numbers to match a known good source.
Use the arrow keys to select the Barometer field
Press 2nd
Press and hold SET (ALARM). Barometer field will blink three times. Release SET. LSD will blink.
Adjust up or down with arrow buttons.
Arrow button left to next field, etc.
Press DONE.

 

[Randall Kayfes]

Since following CW2274's advice and substituting the Vue console, my quality checks for barometer have been two thumbs up ever since - Davis firmware update for VP2 is long overdue to correct this problem...🤣

[CW2274]

Davis firmware update for VP2 is long overdue to correct this problem...🤣

Well, it's not a problem for those that don't care about the altimeter setting. As far as "correcting" it, not gonna happen. I rattled a supervisor's chain at Davis a good six years ago about making the altimeter setting available for the VP2 console, it ain't here yet, nor will it be. Marketing 101 in effect, if you want it badly enough, you'll buy it. Got me twice. 

[lightmaster]

So if the nearest airport's "pressure" is 29.63inHg and my station is reporting SLP as 29.63inHg after 24 hours since I adjusted it, then my station is "good enough" until I buy the Vue Console?

[gszlag]

So if the nearest airport's "pressure" is 29.63inHg and my station is reporting SLP as 29.63inHg after 24 hours since I adjusted it, then my station is "good enough" until I buy the Vue Console?

How did you end up calibrating? Did you match your station pressure with the mesowest pressure for Baxley?
If so, you should be closely matching SLP with Alma [Baxley doesn't report SLP].
Since your current console only calculates SLP you should be matching Alma's SLP (KAMG) at 6:53 AM EST like so:

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Your console should be showing 29.83 inHg.

[lightmaster]

So if the nearest airport's "pressure" is 29.63inHg and my station is reporting SLP as 29.63inHg after 24 hours since I adjusted it, then my station is "good enough" until I buy the Vue Console?

How did you end up calibrating? Did you match your station pressure with the mesowest pressure for Baxley?
If so, you should be closely matching SLP with Alma [Baxley doesn't report SLP].
Since your current console only calculates SLP you should be matching Alma's SLP (KAMG) at 6:53 AM EST like so:

Your console should be showing 29.83 inHg.

When I added my station to Ambient Weather's site, they gave a relative pressure for Baxley's Airport and I used that to calibrate mine. Just looked and the relative pressure for both KBHC and KAMG are within 0.01 inHg of each other.

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[gszlag]

So if the nearest airport's "pressure" is 29.63inHg and my station is reporting SLP as 29.63inHg after 24 hours since I adjusted it, then my station is "good enough" until I buy the Vue Console?

How did you end up calibrating? Did you match your station pressure with the mesowest pressure for Baxley?
If so, you should be closely matching SLP with Alma [Baxley doesn't report SLP].
Since your current console only calculates SLP you should be matching Alma's SLP (KAMG) at 6:53 AM EST like so:

Your console should be showing 29.83 inHg.

When I added my station to Ambient Weather's site, they gave a relative pressure for Baxley's Airport and I used that to calibrate mine. Just looked and the relative pressure for both KBHC and KAMG are within 0.01 inHg of each other.

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Well, how about that!.Ambient is correct! Baxley does have a SLP reading.

Curiously, Baxley does not show SLP in their METAR - just Altimeter but I took another look at Baxley mesowest and darn - there it is. You have both Altimeter and SLP...at least on mesowest.

Obviously this makes things a bit easier as you can better match the closer Baxley SLP instead of the farther Alma SLP.

Yeah, definitely more than good enough until you decide to by the Vantage Vue console.

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[Jim_49]

After reading this thread and other threads and the VP2 console User Manual my brain is all wrapped in knots over the different pressures that are discussed.  The pressures discussed in these sources are atmospheric pressure, SLP, barometric pressure, altimeter and pressure as reported by MesoWest.  The VP2 console User Manual states in Appendix A that the console measures atmospheric pressure and converts it to barometric pressure.  It also states in the Weather Data Specifications that barometric pressure readings are standardized to sea level.  I live just outside Ottawa, Kansas.  The local airport is Ottawa Municipal Airport, ID KOWI.  MesoWest reports Pressure and Altimeter.  I have the following questions:

1.  Is the value that the VP2 console displays and reports the same as SLP?
2.  Is what the VP2 console User Manual calls barometric pressure the same as SLP?  (Probably the same question as question 1.)
3.  Is the Pressure value that MesoWest reports the same as what the VP2 console User Manual calls atmospheric pressure?
4.  When following the Calibrating Barometric Pressure instructions in the VP2 console User Manual are you entering what the manual refers to as atmospheric pressure or barometric pressure (SLP?)?
5.  The distance between my location and the airport is approximately 11 miles and the difference in elevation is approximately 25 to 30 feet.  Can I use the data in the MesoWest report to calibrate the pressure in my console?

Thanks in advance.

[gszlag]

After reading this thread and other threads and the VP2 console User Manual my brain is all wrapped in knots over the different pressures that are discussed.  The pressures discussed in these sources are atmospheric pressure, SLP, barometric pressure, altimeter and pressure as reported by MesoWest.  The VP2 console User Manual states in Appendix A that the console measures atmospheric pressure and converts it to barometric pressure.  It also states in the Weather Data Specifications that barometric pressure readings are standardized to sea level.  I live just outside Ottawa, Kansas.  The local airport is Ottawa Municipal Airport, ID KOWI.  MesoWest reports Pressure and Altimeter.  I have the following questions:

1.  Is the value that the VP2 console displays and reports the same as SLP?
2.  Is what the VP2 console User Manual calls barometric pressure the same as SLP?  (Probably the same question as question 1.)
3.  Is the Pressure value that MesoWest reports the same as what the VP2 console User Manual calls atmospheric pressure?
4.  When following the Calibrating Barometric Pressure instructions in the VP2 console User Manual are you entering what the manual refers to as atmospheric pressure or barometric pressure (SLP?)?
5.  The distance between my location and the airport is approximately 11 miles and the difference in elevation is approximately 25 to 30 feet.  Can I use the data in the MesoWest report to calibrate the pressure in my console?

Thanks in advance.

I feel your pain. I do.

re: definition of barometric presure:

Wikipedia: Atmospheric pressure, also known as barometric pressure
NOAA & NWS : Barometric Pressure - the pressure of the atmosphere as indicated by a barometer.

As you can see, the use of the term “barometric pressure” is somewhat ambiguous. So is the term “SLP”. In the U.S. it appears that barometric pressure can refer to either atmospheric pressure or SLP. In academia, SLP can refer to either Altimeter( setting)/QNH or QFF.

Although personal preferences and common/popular usage can be different, once you add regional and country differences you have a Tower of Babel scenario. In Europe, SLP and Altimeter are not used in METAR(some military airfields excepted). It is just QNH over there but in Europe, “air pressure” is commonly used.

I think the aviation world is far more clear. They use the "Q"codes. No confusion with QFE, QNH and QFF.

For meteorological purposes for our personal weather stations (pws), I prefer the following terminology. Note the absence(intended) of barometric pressure, atmospheric pressure and air pressure.

Pressure/Station pressure = calibrated station pressure at your sensor elevation. Unlike airports, we assume that sensor pressure = station pressure.

Altimeter/QNH = station pressure that is elevation corrected.

SLP/MSLP/QFF = station pressure that is elevation and temperature corrected (sometimes there are additional corrections for humidity and plateau effect)

Your Davis console (unless you have the Vue console) calculates SLP only so I suspect your manual's "barometric pressure" is probably referring to SLP.

"Atmospheric pressure" is reported as "Pressure" in Mesowest.

I do not own a Davis weather station but I believe when you are in "adjust barometer mode" you are adjusting atmospheric pressure/station pressure.
Perhaps a Davis owner can confirm this.

The elevation difference between you and your airport is immaterial as SLP normalizes all pressures down to sea level elevation. SLP is a calculated value - calculated by your console.

[gszlag]

Could be that I am wrong about what the VP2 console buttons do?

From the Davis VP2 manual:

Calibrating Barometric Pressure

Before calibrating the barometric pressure, be sure the station is set to the correct elevation. See “Screen 10: Elevation” on page 16 for more information.

1. Press BAR to select barometric pressure.
2. Press and release 2ND, then press and hold SET.
The pressure variable blinks.
3. Continue holding the key until the ticker reads “set barometer . . . ”.
4. Press the < and > keys to select digits in the variable.
5. Press + and - keys to add to or subtract from the digit’s value.
6. Press DONE to exit calibration.

It looks like you can adjust SLP value directly?

[lightmaster]

Here's what I did:

First, found that my town's airport is about 3 miles away and their sensor is within a few feet of mine, so all of my pressure numbers should conveniently be the same. I set on my console the correct altitude above sea level that my console sits. On a decent day where I expect the pressure to be pretty consistent all day, I looked at the MesoWest page for the airports "pressure in" and once it updated again (updated every 20 mins) I set my console to show the same pressure as the "pressure in" as MesoWest shows for the airport. 24 hours later, I tweaked it again to make sure it was still the same. Even now it still shows almost the exact same pressure (within 0.01 inHg) for both stations' "pressure in" and "altimeter in" and CWOP shows 2 thumbs up for the barometer graph.

[gszlag]

Here's what I did:

First, found that my town's airport is about 3 miles away and their sensor is within a few feet of mine, so all of my pressure numbers should conveniently be the same. I set on my console the correct altitude above sea level that my console sits. On a decent day where I expect the pressure to be pretty consistent all day, I looked at the MesoWest page for the airports "pressure in" and once it updated again (updated every 20 mins) I set my console to show the same pressure as the "pressure in" as MesoWest shows for the airport. 24 hours later, I tweaked it again to make sure it was still the same. Even now it still shows almost the exact same pressure (within 0.01 inHg) for both stations' "pressure in" and "altimeter in" and CWOP shows 2 thumbs up for the barometer graph.

You have a a great advantage. You can just set your station pressure to be the same as the airport because you are at the same elevation. Very nice.

However for the OP, the elevations are different so he can't directly match his airport's station pressure. I will reply to the OP for some additional things he can try.

[gszlag]

@Jim_49

SLP(Sea Level Pressure) is not available for KOWI METAR or KOWI Mesowest.

The closest METAR SLP is KEMP and one could  calibrate to that SLP value when you and KEMP are in the same pressure zone.

Can you calibrate to Altimeter? Yes, but your console doesn't calculate Altimeter directly so you have to use a fixed offset(set elevation to zero) to approximate its value. You would have to purchase a Davis Vue console to calculate Altimeter with greater accuracy.

I guess the question is - what pressure do you want to track? Altimeter or SLP? Or both?

[CW2274]

@Jim_49

SLP(Sea Level Pressure) is not available for KOWI METAR or KOWI Mesowest.

The closest METAR SLP is KEMP and one could  calibrate to that SLP value when you and KEMP are in the same pressure zone.

Here's the AirNav for KOWI. Under "Airport Communications", you find this.. WX AWOS-2 at K68 (16 nm S):122.8 (785-448-3254) (freq. & phone # for the AWOS)

https://www.airnav.com/airport/KOWI

And here's K68, which is 16 nm away vs 50 nm from KEMP.

https://www.airnav.com/airport/K68

[Jim_49]

Thanks for everyone's help.  I now understand that atmospheric pressure (Davis term), station pressure and pressure as reported by MesoWest are the same thing.  I also now understand that what Davis calls barometric pressure and SLP are the same thing.  I contacted Davis concerning their calibration instructions.  What is entered is atmospheric pressure.  The console then calculates and displays barometric pressure (SLP) based on the altitude previously entered.