DIY Barometer (was barograph)

[nigelmercier]

... So I'm back to the idea of making a compact device which will show:
[1] Current absolute pressure with barograph display
[2] Current pressure with trend display and alarm...

Coming back to this again, I'm beginning to think that a barograph display won't be as useful to me as a set of symbols denoting the pressure change and some kind of indication of the trend. I would prefer to stick with one screen, so my options are limited.

The current prototype looks like this:

The first two lines are self explanatory. The third shows the pressure change since the last reading (one hour ago, so Pa/hr) and a symbol showing the pressure is steady. The fourth line will eventually show a horizontal bar-graph (not a barograph) that steps through the last eight readings, pausing on the last.

I have a number of symbols: Fast rise, show rise, steady, slow fall, fast fall; the latter will raise an alarm.

I welcome suggestions on suitable values in Pa/hr for these symbols, and any comments.

 

[Deleted member 36384]

On some heart beat readouts on training watches you get a symbol, heart for example, with bars above it or below it depending on training zone and heart rate change. In your case you could have say an apex up triangle for rising pressure and then bars e.g. 1 bar for a certain rate of change, then 2 bars for the faster rate of change, 3 bars for the rate of change that indicates 'imminent', maybe in this case the 3 bars could also flash.

I like the idea you have, simple and easy.

The met office has a page on rates of pressure change associated with expected timing of wind strengths: -

Pressure tendency in station reportsRising (or falling) more slowly


Pressure rising (or falling) at a progressively slower rate through the preceding three hours


Rising (or falling) slowly


Pressure change of 0.1 to 1.5 hPa in the preceding three hours


Rising (or falling)


Pressure change of 1.6 to 3.5 hPa in the preceding three hours


Rising (or falling) quickly


Pressure change of 3.6 to 6.0 hPa in the preceding three hours


Rising (or falling) v. rapidly


Pressure change of more than 6.0 hPa in the preceding three hours


Now rising (or falling)


Pressure has been falling (rising) or steady in the preceding three hours, but at the time of observation was definitely rising (falling)


Note: For those more familiar with the millibar, 1 hPa = 1 mb

From here: http://www.metoffice.gov.uk/guide/weather/marine/glossary

See table 47 in the link below which has simple plotting symbols for pressure change: -

http://www.metoffice.gov.uk/media/pdf/a/t/No._11_-_Weather_Charts.pdf

 

[nigelmercier]

Thanks for info, now all working. So given that the forecast says:

Slow: Pressure change of 0.1 to 1.5 hPa in the preceding three hours (< 50Pa/h)
Unspecified: Pressure change of 1.6 to 3.5 hPa in the preceding three hours (< 116 Pa/h)
Quickly: Pressure change of 3.6 to 6.0 hPa in the preceding three hours (< 200 PA/h)
Very rapidly: Pressure change of more than 6.0 hPa in the preceding three hours (>200 Pa/h)

I'm taking my measurements every hour, hence the figures in brackets converted to Pa/h

At what pressure drop should I sound an alarm?

 

[rogerthebodger]

At what pressure drop should I sound an alarm?

Why don't you make the rate of pressure drop user adjustable.

 

[Deleted member 36384]

I would suggest that the alarm should be set for "Very Rapidly" as this is the warning that we look for imminent strong to gale force winds. I think that "quickly' is likely to forecast strong winds; say 170 Pa/h alarm point.

Email Dr Simon whats his name, he would very much understand the reality of wind strengths and pressure drop and could advise.

This links give expected wind strength in Beaufort for pressure change rates: http://www.bohlken.net/airpressure2.htm

 

[nigelmercier]

My current version of my DIY Barometer screen display, with rather phallic looking arrow! (see new arrows below)

Line 1 is the ambient temperature, line 2 is the absolute calibrated pressure.
Line 3 is now showing the trend arrow and the rate from the last reading in Pa/h
Ignore the 60 far right, just debug info.
The last line shows the last 8 hourly values (they appear one at a time) and a marker showing the current value as a reference. Not as good as a barograph perhaps, but better than the average weather station.

My new arrows*:
Falling Very Rapidly (>200 Pa/h), Falling Quickly (116 - 200 Pa/h), Falling (50 - 116 Pa/h)
Slow (< 50 Pa/h Steady)
Rising (50 - 116 Pa/h), Rising Quickly (116 - 200 Pa/h), Rising Very Rapidly (>200 Pa/h)

The logic behind these is that the solid arrows represent a warning. I also have the option of sounding an alarm independent of the arrow, so opinions are welcome.

*They look a bit clunky here, but the screen width is only 32mm with 128 pixels, so each pixel is 0.25mm

 

[Deleted member 36384]

Top Banana Mr Mercier.

 

[simonjk]

Hi Nigel,

Love it!

I think the definition you are using for tendency are okay. Much would depend on where you are sailing, but I think those that you have are certainly acceptable.

Look fabulous though....well done! At Weather School I am always going on about the value of barometers/barographs so this is a real useful tool, especially as it is calibrated to 1/10ths hPa.

Keep up the good wrk!
Simon