Montana Barometer Issues

[yogazoo]

In test after test I've been experiencing the same result using the barometric pressure plot on the Montana 650 using software version 3.66 and 3.67.

 

What I'm finding is that if I leave my unit on in a stationary location the pressure refuses to change and you get the plot seen below. There is not only a lack of dynamic data but there is simply no change in pressure data period. Again the unit was on and battery save mode was off. Notice the time in the upper left of the plot images.

 

 

 

Using a second Montana unit I found similar results in "Save Always" mode and then turned OFF(below). From power down to power up you get a straight line (no data). Notice the time in the upper left.

 

 

These tests were conducted after a careful manual calibration of the altimeter. One important observation I noticed was that the only time the pressure changed was when I first powerd on the unit (first reading). After that i get a straight line in both scenarios.

Is anyone else experiencing similar results? Anyone care to set your unit up with the same settings for a few hours to see if you get anything different than what's below?

Edited December 16, 2011 by yogazoo

[+Subraid]

Yes, I've exactly the same problem with my Montana and FW 3.6x Beta.

The "always pressure saving" worked well with FW 3.60.

[+mpilchfamily]

I could be wrong but isn't that normal. If your not moving up and down in altitude its not going to show a change, right? It seems to me the unit will have a fair degree of margin in the amount of pressure difference it detects and what it plots. I don't know how much the barometric pressure will change over the course of a day or how big of a margin the unit works with. But it seems that whatever the difference is, over the course of a few hours while sitting in a stationary position, isn't enough to register on the unit.

 

have you tried moving up and down a couple hundred feet in elevation to see how it plots? Or is that not the kind of data your looking for? Are you trying to treat the GPSr like a weather instrument?

[yogazoo]

I could be wrong but...

 

Please forgive my candid retort but, yes, you are. Barometric Pressure recording is a recording of the altitude adjusted ambient pressure readings. It WILL fluctuate over any given time period at a given altitude. Look on Weather Underground for your towns data and take a look at the pressure trending, same thing, VERY dynamic data recorded at a static location (usually an airport).

 

No I have not tried moving up or down but then again the adjusted barometric pressure is a function of altitude but fluctuations in pressure (rising or falling barometer) are independant of altitude (resulting from changing weather patterns). Since I'm not seeing any changes it doesn't matter whether or not I move up or down, that's not what I'm after.

 

PLUS the adjusted barometric pressure (resulting from weather patterns) stays the same in the unit that remains ON constantly. In nature that would be an extreme anomaly and has never happened.

 

Are you trying to treat the GPSr like a weather instrument?

Yes

 

I've used pressure trending plots going all the way back to the 60C ("Save Always" wasn't a feature in the CSX) through all models of current units. I'm not conducting the test wrong or expecting unwarranted results, there is a problem with the plotting on my unit and I'm simply attempting to survey the scope of the issue to see how pervasive it really is. The entire point of the altitude adjusted barometric pressure plot is to observe weather trends so YES I'm attempting to use my unit as a weather instrument, which is the entire point of this feature as stated on Garmins own Website.

 

And I quote the Montana 650 page of their website: https://buy.garmin.com/shop/shop.do?pID=75227

 

"...and you even can use it to plot barometric pressure over time, which can help you keep an eye on changing weather conditions."

Edited December 16, 2011 by yogazoo

[yogazoo]

...same problem with my Montana and FW 3.6x Beta.

...worked well with FW 3.60.

 

Ahh, now we're getting somewhere. Garmin, you reading this? Something in the changes between these firmware versions have caused the issues we're experiencing.

[+splashy]

I had Barometer issues with Oregon, then it worked, after again issues, now I have the same with Montana.

They seem to forget about this because it happens too often.

 

Actually I gave up, just tried again because of this thread and surprise, it's not working (for now).

Edited December 16, 2011 by splashy

[WrongwayUK]

In test after test I've been experiencing the same result using the barometric pressure plot on the Montana 650 using software version 3.66 and 3.67.

 

What I'm finding is that if I leave my unit on in a stationary location the pressure refuses to change and you get the plot seen below. There is not only a lack of dynamic data but there is simply no change in pressure data period. Again the unit was on and battery save mode was off. Notice the time in the upper left of the plot images.

 

 

I notice you have the Barometer Mode set to Variable Elevation. I would have thought it should be set to fixed elevation as your in a fixed location monitoring a pressure trend. I think last time I tried the test I had the setting at Fixed Elevation and it seemed to work. I will try again. Incidentally if I set mine to Variable Elevation it shows an incorrect barometric pressure as I am inside the house, no decent sat fix as a reference of height. Thats why I think fixed elevation should be used.

Edited December 17, 2011 by WrongwayUK

[yogazoo]

WrongwayUK,

 

It may seem as though fixed elevation should be used and that I should set it to fixed elevation but that's not how this plot has worked since Garmin introduced the feature.

 

Think of it this way, in Variable Elevation mode the GPS takes the ambient pressure and calculates the adjusted sea-level barometric pressure using continuous GPS elevation data. It doesn't matter whether I'm standing still or climbing a mountain, all the calculation consists of is ambient pressure and the current elevation value from the satellites. That's it, pure and simple. The plot is a record of that data over time.

 

In Fixed Elevation mode, the barometer stops using continuos GPS elevation data to adjust to sea level. It's DOES adjust the pressure to sea level but instead of using continuous data is simply records the elevation at the start (when Fixed Mode is entered or another point in the process). SO it doesn't correct for elevation changes it's simply an identical plot as the ambient pressure only it's adjusted to sea level ONCE but not continuously like in Variable mode. The asumption is that you can get a better read on the barometric pressure if it's set to a constant elevation, like on a lake or at a basecamp or weather station where your elevation won't change. This mode does not subject the pressure reading to satellite error.

 

This is how it's worked in the past, with every unit since the early 60C. Now with every generation of new Garmin we have to struggle through this barometer issue, Colorado, then Oregon, then 62S, now the Montana.

Edited December 17, 2011 by yogazoo

[yogazoo]

Another issue regarding the barometer;

 

When using units of Hg (inches of mercury) for pressure readings, which is most of the US, you can only calibrate to a single digit after the decimal point. The unit of Hg is significant to TWO digits after the decimal point. Only calibrating Hg to a single digit equates to an elevation error of potantially over 100 feet making any kind of accuracy in calibration nearly impossible unless you get lucky and the observed current second digit is on or near zero.

 

You can calibrate to all the significant digits using the other pressure units, why not Hg (inches of mercury)? For example if you're using millibars, each consecutive number to the left of the decimal point equals about 30 feet and if you calibrate the Montana using these units it allows you to adjust to one digit after the decimal point (tenths) which would be about 3 feet difference for each subsequent number.

 

So in summary, if you're calibrating to a known pressure using inches of mercury (Hg), like most of America is, you can only adjust to a resolution of 100 feet in elevation. If you use millibars or Hpa you can calibrate to within 3 feet. It just doesn't make sense.

 

I've noticed this for a long time and kept looking for a fix because it's such an elementary ommission. It doesn't fill me with great deal of confidence that a whole lot of thought was placed behind the barometric altimeter function.

Edited December 17, 2011 by yogazoo

[WrongwayUK]

WrongwayUK,

 

It may seem as though fixed elevation should be used and that I should set it to fixed elevation but that's not how this plot has worked since Garmin introduced the feature.

 

 

When you did the test did you have a constant good satellite lock over the test period?

[yogazoo]

When you did the test did you have a constant good satellite lock over the test period?

 

Absolutely. I went to bed and counted 10 satellites with 15 ft EPE.

[WrongwayUK]

Mines sat on the window sill at the moment and has been for the last 3 hours using your settings. So far I can see a trace thats changing though the digital display of baro pressure at the top hasn't changed. So I am a bit confused now. I would have thought the digital baro field I have set up would match the trace.

Edited December 17, 2011 by WrongwayUK

[39_Steps]

Fix the fixed elevation feature when not using a satellite fix?

[yogazoo]

Mines sat on the window sill at the moment and has been for the last 3 hours using your settings. So far I can see a trace thats changing though the digital display of baro pressure at the top hasn't changed. So I am a bit confused now. I would have thought the digital baro field I have set up would match the trace.

 

Thanks for taking the time to test it out. So you ARE getting dynamic data being recorded? Wow, the 4 guys I know in town here who have a Montana get the same results I do, straight line.

[WrongwayUK]

Will post results later

[WrongwayUK]

These are the results from the Montana sitting on the window sill all afternoon. As you can see it tracked pressure on the graph.Ignore the lump at the beginning. Thats where I calibrated and set to variable elevation.

It's strange watching the graph but the digital reading was static.

 

Settings

Note Baro digital reading stayed at 1006 the whole time

[stebu]

These are the results from the Montana sitting on the window sill all afternoon. As you can see it tracked pressure on the graph.Ignore the lump at the beginning. Thats where I calibrated and set to variable elevation.

It's strange watching the graph but the digital reading was static.

On my Dakota 20 you can select "Ambient pressure", which seems to react swiftly to pressure changes.

[yogazoo]

These are the results from the Montana sitting on the window sill all afternoon. As you can see it tracked pressure on the graph.Ignore the lump at the beginning. Thats where I calibrated and set to variable elevation.

It's strange watching the graph but the digital reading was static.

On my Dakota 20 you can select "Ambient pressure", which seems to react swiftly to pressure changes.

Ambient Pressure is, for the most part meaningless. Yeah, it will show you the ambient trend but it's not adjusted for sea level and it's not adjusted for elevation.

[yogazoo]

These are the results from the Montana sitting on the window sill all afternoon. As you can see it tracked pressure on the graph.Ignore the lump at the beginning. Thats where I calibrated and set to variable elevation.

It's strange watching the graph but the digital reading was static.

 

Note Baro digital reading stayed at 1006 the whole time

 

WrongwayUK, your plot looks wierd but it's better than mine. It's wierder that your barometric pressure reading stayed the same the whole time.

 

I think we've collectively confirmed beyond a reasonable doubt that there IS an issue here.

 

I've reverted back to firmware version 3.60 so I can actually use this functionality. I'll wait for Garmin to issue a fix to this before upgrading further.

Edited December 17, 2011 by yogazoo

[+A.T.Hiker]

I have beta version 3.66 and I can tell you pressure trending while power off is toasted on my unit too. In fact, I get some really strange gaps in the data upon power-up where it seems to have briefly dropped to zero pressure before returning to the current reading. I am not tech savvy when it comes to posting screen shots, but it's definately not able to provide barometric or ambient pressure trending as advertised.

 

Only work around I could think of would be to leave it powered on with GPS in demo mode and battery saver switched to on. But it's not really supposed to have to be used that way.