### Author Topic: Barometer error  (Read 5727 times)

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#### nincehelser

• Forecaster
• Posts: 2907
##### Re: Barometer error
« Reply #25 on: February 19, 2016, 04:08:43 PM »

Also, in the limit where hm=0 (sea level, zero height), the Altimeter is the absolute pressure in mb - 0.3.  Is this correct?

In reality, no.  Altimeter is just an approximation based on assumptions of how the atmosphere works.  Even the concept of pressure at "sea level" has some assumptions built in.

#### waysta

• Contributor
• Posts: 148
##### Re: Barometer error
« Reply #26 on: February 19, 2016, 07:25:50 PM »
okay, just when I was about convinced the NOAA equation has some typo, I found this similar version:

http://www.allweatherinc.com/wp-content/uploads/7190-0011.pdf page 6: "Altimeter Setting Check Use the formula below to calculate Altimeter Setting from the barometric pressure measured using the Model 7101 pressure standard. Record the calculated altimeter setting and that reported by the AWOS on the annual data form."

Alt.Setting(inHg)=(BPα + SE ⋅1.313⋅10−5 )5.25486 )⋅100 where: α = 0.1903 SE = Sensor elevation above sea level in feet BP = Barometric pressure in inHg

This one gives values closer to the NOAA formula, although the last x100 looks wrong.  I need to check my math, it is not credible for the Davis equation and this variant to give such different results (if the equations are correct).
« Last Edit: February 19, 2016, 07:29:12 PM by waysta »

#### hankster

• Forecaster
• Posts: 479
##### Re: Barometer error
« Reply #27 on: February 19, 2016, 07:28:51 PM »

Bloom Sky error about  ~+.20 in Hg (to my RainWise)

Mine is also off ~+20

The Dashboard is only off 1
« Last Edit: February 19, 2016, 07:31:16 PM by hankster »

#### nincehelser

• Forecaster
• Posts: 2907
##### Re: Barometer error
« Reply #28 on: February 19, 2016, 11:11:25 PM »

Bloom Sky error about  ~+.20 in Hg (to my RainWise)

Mine is also off ~+20

The Dashboard is only off 1

If this ~+20inHg is widespread, it would lead me to believe that Bloomsky is not reading/computing the absolute pressure correctly from the sensor chip.

If true, that should be easily addressed with a firmware update, probably one that they can push from their end.

#### hankster

• Forecaster
• Posts: 479
##### Re: Barometer error
« Reply #29 on: February 20, 2016, 09:10:22 AM »

Bloom Sky error about  ~+.20 in Hg (to my RainWise)

Mine is also off ~+20

The Dashboard is only off 1

If this ~+20inHg is widespread, it would lead me to believe that Bloomsky is not reading/computing the absolute pressure correctly from the sensor chip.

If true, that should be easily addressed with a firmware update, probably one that they can push from their end.
Heck,  they may not even need a firmware update. Since all the raw data goes to the cloud they just need to change the software on their serves to compensate. Other then the WU info would be wrong, but AFAWK the station may not report directly to WU but goes through the BloomSky servers first and the servers report to WU (which is what I think happens).
« Last Edit: February 20, 2016, 09:13:57 AM by hankster »

#### nincehelser

• Forecaster
• Posts: 2907
##### Re: Barometer error
« Reply #30 on: February 20, 2016, 09:32:42 AM »
Heck,  they may not even need a firmware update. Since all the raw data goes to the cloud they just need to change the software on their serves to compensate. Other then the WU info would be wrong, but AFAWK the station may not report directly to WU but goes through the BloomSky servers first and the servers report to WU (which is what I think happens).

That's possible if they are reading the sensor data correctly and sending it correctly to Bloomsky.

Where the absolute pressure calculation is done is unclear, but I suspect it's on the servers.

The data does flow through Bloomsky first.  Bloomsky sends the data to WU via their portal, which is why WU is getting "absolute" pressure.

#### waysta

• Contributor
• Posts: 148
##### Re: Barometer error
« Reply #31 on: February 20, 2016, 05:24:58 PM »
My spot check this afternoon is "closer":

4:58 pm (EST) Bloom Sky iOS 29.78 -  RainWise WU 29.72
5:06 29.81 - 29.72
5:09 29.78 - 5:08 29.72
5:12 29.81 - 5:13 29.73
5:18 29.81 - 29.73

Still tracking (as realized by nincehelser sometime back, there are two very different reported Bloom Sky barometer values, this is the iOS data) 46 F (heatwave today, got in a walk to the village!)
8:02 pm 29.90 - 8:03 29.82

Barometer data this close is very new for me, previously my closest numbers (the iOS data) were about 0.2 in Hg apart.

aargh! Bloom Sky shows the new data with a current time, but the same picture on WU says it is 2 hours old.  I noticed because the moon is bright and high in the sky, but not on my sky image.
« Last Edit: February 20, 2016, 08:35:32 PM by waysta »

#### nincehelser

• Forecaster
• Posts: 2907
##### Re: Barometer error
« Reply #32 on: February 20, 2016, 05:51:58 PM »
Mine seems to be maintaining a consistent 8mb difference.

#### sacreyweather

• Echo Valley Weather
• Forecaster
• Posts: 1727
##### Re: Barometer error
« Reply #33 on: February 20, 2016, 06:27:01 PM »
Mine has been averaging about a -0.30 inHg difference from my Davis VP2 for the last 2 days. The temps and humidity have been real close.
CWOP: D2073, GR2AE, GR3, Cumulus, PWSweather,  CoCoRaHS: AR-SL-23

Blitzortung Station 1387

#### waysta

• Contributor
• Posts: 148
##### Re: Barometer error
« Reply #34 on: February 21, 2016, 10:24:55 AM »
My differences are changing now, makes no sense, unless maybe the BSky barometer (sensor and/or circuit) an/or BSky altimeter equation has a temperature sensitivity.  This morning at about 38F, the barometer (altimeter) difference (BSky iOS to RW) is +0.12

BSky  data portal: 10:11 1000 mb (29.53)
BSky  WU: 10:07 29.53 39.1F
http://www.wunderground.com/personal-weather-station/dashboard?ID=KNYWHITE25

BSky web: 10:06 1020 mb (30.12)
BSky  iOS:  10:11 30.12

RW: 10:08 30.00 38.3
http://www.wunderground.com/personal-weather-station/dashboard?ID=KNYWHITE24

My BSky picture is updating normally this am.  Otherwise, the BSky graphs and data tables, both BSky and WU show no interruption of data last night when the webcam stopped updating on iOS and the latest pic was getting hours old on WU.

The BSky FAQs seem to do ask folks to do a reset anytime there is an anomaly, however with the unit on a pole on the roof, pushing the buttons on the ball is not so easy for me.
« Last Edit: February 21, 2016, 10:38:19 AM by waysta »

#### RF Burns

• Member
• Posts: 4
##### Re: Barometer error
« Reply #35 on: March 03, 2016, 06:17:42 AM »
My station is reporting 30.24 and these local airports are way different.We are all at same elevation.No reply yet on support email submitted.

KAPF 031053Z 02005KT 10SM CLR 18/14 A3005 RMK AO2 SLP174 T01780144
KRSW 031053Z 02004KT 10SM CLR 16/11 A3006 RMK AO2 SLP176 T01610106

#### RF Burns

• Member
• Posts: 4
##### Re: Barometer error
« Reply #36 on: March 06, 2016, 06:40:42 AM »
My station is reporting 30.24 and these local airports are way different.We are all at same elevation.No reply yet on support email submitted.

KAPF 031053Z 02005KT 10SM CLR 18/14 A3005 RMK AO2 SLP174 T01780144
KRSW 031053Z 02004KT 10SM CLR 16/11 A3006 RMK AO2 SLP176 T01610106

The barometer reporting is now missing on the station, as to why, I would love to know. Any guesses? BTW yesterdays time lapse is stunning. Be sure to favorite if you like. https://map.bloomsky.com/weather-stations/gqBxp6apnJSnnJ6q

#### ocala

• Forecaster
• Posts: 3587
##### Re: Barometer error
« Reply #37 on: April 17, 2016, 09:32:19 AM »
Just got mine Friday and installed Saturday.
So far the readings are almost in line with my Davis.
As of this moment,
Davis Temp- 66  Bloomsky Temp- 66
Davis Humidity- 88%  Bloomsky Humidity-91%
Davis Pressure- 30.245  Bloomsky Pressure- 30.24

#### VaJim

• Virginia Beach Backyard Weather
• Forecaster
• Posts: 727
##### Re: Barometer error
« Reply #38 on: June 28, 2016, 08:03:48 AM »
Where is everyone seeing the correct pressure on their Bloomsky?

Most of the time I'm looking at mine through the website map and the pressure is still off.