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Old 14-02-2019, 17:05   #1
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Barometric pressure calculations

For background I'm writing software to take barometric pressure readings from an on-boat sensor, then put both the current reading and the trend (increasing/decreasing/constant) up on a screen. I could take readings say as often as a few times a second, but, those reading would become basically noise. So I am thinking I take a barometric pressure reading every 1? 2? 3? other? minute(s) collect readings for the last 1? 2? 3? 4? other? hour(s) to calculate an average. If the current pressure reading is more than the average by 0.2? 0.5? 1? other? mB assume there is an upward trend, if the current reading is within 0.2? 0.5? 1? other? mB assume the trend is constant and if the pressure has dropped by more than whatever assume the trend is downwards.

In other words I am trying to figure out limits,

- How often should I sample pressure?
- Over what time frame should I track pressure averages?
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Old 14-02-2019, 21:49   #2
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Re: Barometric pressure calculations

Where are you planning to use it. You need to consider diurnal variation if looking for averages and whether there is a significant rise or fall.


In the tropics diurnal variation alone can be about 3 millibars over 6 hours
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Old 15-02-2019, 00:35   #3
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Re: Barometric pressure calculations

The trend should be mb/hr change.
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Old 15-02-2019, 02:43   #4
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Re: Barometric pressure calculations

The international unit of meteorological air pressure is hectopascals (hP), which is equivalent to millibars (mb).
Standard air pressure at sea level is 1013.25 mb. The highest air pressure recorded was 1084 mb in Siberia. The lowest air pressure, 870 mb, was recorded in a typhoon in the Pacific Ocean.
Air pressure rises and falls about 3 mb in daily cycles, regardless of weather. Meteorologists take these fluctuations into account when they analyze changes in air pressure to interpret if the changes are due to weather systems. A large drop of 7 mb or more, in 24 hours, may indicate a high-pressure system is moving out and/or a low-pressure system is moving in.

ASOS Pressure Algorithm ~ National Weather Service Training Center

Once every ten seconds the two digital barometers (Class I system) or three digital barometers (Class II system) provide pressure readings for the observing site.
If you have a Class I system with two barometers, the six readings taken every minute are sent to algorithms for processing and comparison. If you have a Class III system with three barometers, the same process occurs but here you have three readings to compare.
If one or more of the 6 pressure values obtained during a one-minute period are missing, the sensor is automatically logged as "inoperative". It can only be returned to "operational status" by a maintenance technician.
Once the sensor data has been determined, the further processing by the pressure algorithms takes place so as to provide additional pressure parameter information

Much more https://training.weather.gov/nwstc/D.../Pressure.HTML
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Old 15-02-2019, 02:58   #5
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Re: Barometric pressure calculations

I would like to see simple line graph for a historical period of 48hrs up to real time with sampling every 15 or 30 minutes. An adjustable notification for change/hours.

Is this going to be available or for your own use, do phones measure air pressure because a phone app would sell.
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Old 15-02-2019, 06:23   #6
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Re: Barometric pressure calculations

Many thanks for the comments. A bit more background, this comes out of a little project that I have been letting spiral out of control. Last August I bought a 1979 31' project boat (low price, lots of issues). Among the issues, incandescent bunk lights (reading lights mounted above each bunk). For several reasons I want those incandescent lights gone, so, current plan is to have LED based bunk lights mounted on top of a hollow plaque, with several devices hidden inside the plaque, including (among other things) an Anduino compatible controller, a small OLED display, and a BME280 temperature/pressure/humidity sensor. In other words, make sure everyone on-board can have some basic information about what is happening on the boat (including some weather related information) by just looking up at their bunk light (well the plaque behind the bunk light). All this to be done at a modest price...
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Old 15-02-2019, 15:47   #7
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Re: Barometric pressure calculations

Quote:
Originally Posted by Dave_S View Post
I would like to see simple line graph for a historical period of 48hrs up to real time with sampling every 15 or 30 minutes. An adjustable notification for change/hours.

Is this going to be available or for your own use, do phones measure air pressure because a phone app would sell.

Yes, a lot of phones have air pressure sensors and there are plenty of android apps.


I like "Barometer Altimeter Deskclock" by Aleksander Ciepela
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Old 15-02-2019, 23:57   #8
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Re: Barometric pressure calculations

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Originally Posted by StuM View Post
Yes, a lot of phones have air pressure sensors and there are plenty of android apps.


I like "Barometer Altimeter Deskclock" by Aleksander Ciepela

Thanks, I might have to drag myself into the modern world and get a smart phone.
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Old 17-02-2019, 22:40   #9
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Re: Barometric pressure calculations

See my posts in this thread: Good android barograph app?
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