Topic: How does automatic barometric pressure calibration work?

[SnowHiker]

It must not be meant for mobile applications for people who like to travel from high to low elevations and such.  Seems that would be another disadvantage to not being able to adjust it manually for each location you may be at for a few days or so.

I guess storm chasers, or people who use barometric pressure to tune equipment or such, probably don't use Acurite.

[Neil_O]

I don't how their algorithm actually works, but after 30 days it is pretty close.  If I compare between my Davis and Local METAR, the console is only +/-0.02 off. I think that is pretty good.

I have found that the agreement is better near the "mean" of 29.92 than at barometric pressures far away from that (e.g., 29.40, 30.40).  The algorithm that AcuRite uses seems to attenuate the reported pressure at the extremes.

The attached description of the algorithm was posted about six months ago.  The simple math used would explain the attenuation of the pressure adjustment as the pressure moves further from the mean of 29.92.

[Jim_S]

The attached description of the algorithm was posted about six months ago.  The simple math used would explain the attenuation of the pressure adjustment as the pressure moves further from the mean of 29.92.

Great catch! Where was that posted? I couldn't find it on Acurite's site.

[Neil_O]

The attached description of the algorithm was posted about six months ago.  The simple math used would explain the attenuation of the pressure adjustment as the pressure moves further from the mean of 29.92.

Great catch! Where was that posted? I couldn't find it on Acurite's site.

I was wrong about the timing - it was about 18 months ago that nincehelser posted this information in this thread:

https://www.wxforum.net/index.php?topic=35771.msg366605#msg366605

[Jim_S]

I was wrong about the timing - it was about 18 months ago that nincehelser posted this information in this thread:

Thanks! If I understand correctly this is only used during the learning period...or is it continuous?

[Neil_O]

I was wrong about the timing - it was about 18 months ago that nincehelser posted this information in this thread:

Thanks! If I understand correctly this is only used during the learning period...or is it continuous?

Nope, that algorithm is used for all measurements.  I had assumed that the AcuRite method calculated an elevation during learning mode, but that's not the case.  If you look one message earlier in the thread that I posted, there's a statement clarifying this:

"The "learning method" doesn't actually estimate an elevation.  It learns your average pressure through sampling for a month, then uses that average scaled against 29.92 to adjust the current absolute pressure reading.

It doesn't have any interaction with the Access.  The displays use their own internal baro sensors for the calculation.

The actual equation is printed in an early 5n1 spec sheet . . ."

[Jim_S]

Nope, that algorithm is used for all measurements.  I had assumed that the AcuRite method calculated an elevation during learning mode, but that's not the case.  If you look one message earlier in the thread that I posted, there's a statement clarifying this:

"The "learning method" doesn't actually estimate an elevation.  It learns your average pressure through sampling for a month, then uses that average scaled against 29.92 to adjust the current absolute pressure reading.

It doesn't have any interaction with the Access.  The displays use their own internal baro sensors for the calculation.

The actual equation is printed in an early 5n1 spec sheet . . ."

Thanks! Like you I assumed it calculated an altitude or offset and then used that after the learning mode.

Right now my Access is reading 30.19, my upstairs display is reading 30.18 and downstairs 30.17 so they are staying pretty close.

[Neil_O]

Nope, that algorithm is used for all measurements.  I had assumed that the AcuRite method calculated an elevation during learning mode, but that's not the case.  If you look one message earlier in the thread that I posted, there's a statement clarifying this:

"The "learning method" doesn't actually estimate an elevation.  It learns your average pressure through sampling for a month, then uses that average scaled against 29.92 to adjust the current absolute pressure reading.

It doesn't have any interaction with the Access.  The displays use their own internal baro sensors for the calculation.

The actual equation is printed in an early 5n1 spec sheet . . ."

Thanks! Like you I assumed it calculated an altitude or offset and then used that after the learning mode.

Right now my Access is reading 30.19, my upstairs display is reading 30.18 and downstairs 30.17 so they are staying pretty close.

Keep checking the readings.  It will be interesting to see if they agree as well with Access at low pressures.  I have found that the difference between the displays and Access varies depending on the pressure.

[Jim_S]

Keep checking the readings.  It will be interesting to see if they agree as well with Access at low pressures.  I have found that the difference between the displays and Access varies depending on the pressure.

Thanks! I will keep an eye on it. Gives me something to do between hand washing and looking out the window.