Garmin 60CSx Altimeter problem

[kenny_lex]

I has a Garmin GPSmap 60CSx and I bought it to get a better hight/elevation reading, but when I start my GPS it often show wrong elevation. I know that I must calibrate the altimeter, but if I calibrate it to (let say) 62 meter it dose change without the GPS is moving.

 

I did a test today and calibrated the altimeter to 62m, but after one hour the revelation eading was 68m. when I did the first test the altimeter setup was set to, "Auto Calibration = off" and "Variable Elevation". Same thing happens with the configuration set to, "Auto Calibration = off" and "Fixed Elevation", but when I had "fixed elevation" it just jumps around 59 to 65 meter.

 

So how shall I calibrate the altimeter to get a god relation reading and what dose the "fixed elevation" settings do? It maybe sounds like a dumb question, but my elevation is changing even I´m not move the GPS and the the altimeter seting is set to Fixed Elevation.

 

P.S Sorry for my bad spelling.

 

EDIT: Also, if I calibrate the altimeter to 62 meter and then go in to look at the compass the altimeter jumps to 66 meter when I return. Can it be so that my GPS is broken?

Edited April 17, 2008 by kenny_lex

[+Team CowboyPapa]

If you are referring to your barometric altimeter which actually reads atmospheric pressure and converts that to altitude, don't worry about calibrating it. They are not much good, so spending a lot of time calibrating them is pretty much a waste of that time.

 

They are better used for weather predictions as when they show increasing altitude (lower pressure) a storm, or inclement weather, is coming; if they show decreasing altitude (higher pressure), the weather will become more fair. Additionally, they will show changes in altitude in response to temperature fluctuations, even if the local pressure is constant.

 

Outside of that, I find them highly useful.

[roybassist]

if I calibrate it to (let say) 62 meter it dose change without the GPS is moving.

The sensor is very sensitive, and the elevation reading will normally fluctuate a little even if you are not moving. A variation of 3m in a short time would be within Garmin’s specification (10 ft).

 

I did a test today and calibrated the altimeter to 62m, but after one hour the revelation eading was 68m. when I did the first test the altimeter setup was set to, "Auto Calibration = off" and "Variable Elevation". Same thing happens with the configuration set to, "Auto Calibration = off" and "Fixed Elevation", but when I had "fixed elevation" it just jumps around 59 to 65 meter.

An hour is long enough for your local barometric pressure to change enough to make a difference of 6m. That may not be what happened, but it is one possible explanation for the first instance. I haven’t ever used “Fixed Elevation” mode, so I can’t comment on the second instance.

 

Also, if I calibrate the altimeter to 62 meter and then go in to look at the compass the altimeter jumps to 66 meter when I return.

I have found that pressing the buttons on the unit will momentarily change the pressure reading. I believe this is because it changes the pressure inside the unit faster than the unit can equalize. But it should return to a value near what it was previously soon after you stop pressing the buttons. Give it a minute or so and see if it settles back to something closer to what it was before you pressed the buttons.

 

Can it be so that my GPS is broken?

Of course it’s one possibility; but I wouldn’t jump to that conclusion just yet.

[OGBO]

I has a Garmin GPSmap 60CSx and I bought it to get a better hight/elevation reading, but when I start my GPS it often show wrong elevation. I know that I must calibrate the altimeter, but if I calibrate it to (let say) 62 meter it dose change without the GPS is moving.....

 

If I understand what you are saying, you are worried about variations in the displayed altitude on your 60CSx when it is in a fixed location. The other posters have basically answered your question, but not very clearly.

 

First, the 60CSx (and other Garmin "S" GPSRs) has a barometric altimeter. "Barometric" means that it uses the pressure of the air to measure the altitude. As you probably know from watching the TV weather reports, air pressure changes with the weather. It also changes on a daily cycle, and even from minute to minute. To get a moderately accurate altitude reading from a barometric altimeter, you have to calibrate it at known locations (places that are well-surveyed reference points, determined by the government surveying office, such as the US Geological Survey or US Coast and Geodetic Survey, or similar organizations in other countries).

 

The 60CSx displays only the barometric altitude, and not the GPS-derived altitude. It uses the ICAO Standard Atmosphere Table to relate the pressure measured by the barometer sensor (the "S" in 60CSx) to the altitude, plus the calibration you feed in. There are 3 ways of calibrating, as you have discovered - a known altitude, a known current barometer reading (get this from the local airport or weather office), or use the GPS-derived altitude (easiest to use in the field, and sufficiently accurate for almost any use).

 

Barometric sensors are generally only accurate to 0.01 inch Hg (originally barometers used a column of mercury, Hg is the chemical symbol for mercury, in a tube to measure air pressure, with sea level air pressure supporting a column of mercury about 30 inches tall). As a rough rule of thumb, air pressure drops by 1 inch per 1000 feet of altitude. So, barometric altimeters are generally good only to the nearest 10 feet or 3 meters (the number Garmin specifies). Since the numbers are rounded off, you will see the reading flickering up and down by 10-20 feet (3-6 meters), all the time.

 

There is no way with Garmin's "S" GPSRs to make them display the GPS-derived altitude in the display all the time. You can see the GPS value in the data window by pressing "menu" and selecting "Show GPS altitude", or when calibrating the altimeter. Otherwise, it is only the barometric altitude, and all the fluctuations that will show.

 

In short, what you are seeing is normal. Don't worry about it.

[kenny_lex]

Thank you for all the answers, but now I have another question.

 

My old eTrex Venture did use the GPS signals from the satellites to calculate the elevation, and it gave me a track profile that was okay for me. Can 60SCx also use the GPS signals to calculate the elevation, is there any way to disable the barometric altimeter?

 

I must say that the 60CSx is a accurate and great GPS, often when I calibrate it and take a long walk the statr elevation and end elevation (same position) just differ with some few meter. Good to make great track profiles.

 

What I´we learn today is that the barometer is also a cool thing to use to see (and maybe predict) weather changes :-)

 

So once more; Thank you for the answers and sorry for my spelling.

[Fschwep]

Thank you for all the answers, but now I have another question.

 

My old eTrex Venture did use the GPS signals from the satellites to calculate the elevation, and it gave me a track profile that was okay for me. Can 60SCx also use the GPS signals to calculate the elevation, is there any way to disable the barometric altimeter?

 

I must say that the 60CSx is a accurate and great GPS, often when I calibrate it and take a long walk the statr elevation and end elevation (same position) just differ with some few meter. Good to make great track profiles.

 

What I´we learn today is that the barometer is also a cool thing to use to see (and maybe predict) weather changes :-)

 

So once more; Thank you for the answers and sorry for my spelling.

 

I found that the 60CSx self-calibrates when you switch it on. It uses the GPS 3D position to reset the barometric pressure altimeter. Just saw it do that: switched it on, it showed 780 m when it got a first fix on satellites. Our house is at 640 m, I was on the first floor so closer to 644. True, a weather depression had passed so pressure had dropped, hence the higher altitude showing. A minute later the Elevation counter on the trip comp screen started counting down, finishing at 649 metres. About 5 metres off the true altitude/elevation is quite good - a normal pressure altimeter will be a lot further off if the weather changes. Also, topo maps usually show elevation lines spaced at 10 or 20 metres, so greater accuracy is not of much use during a hike or, like with me, in the air.

Do realize that determining a position within 10 metres horizontally and and vertically on the scale of the PLANET is in fact awesome. It is within the size of a pencil dot on a military 1:50.000 scale map. People are getting too spoiled by car GPSes used as address seekers, while we are talking about the Global Positioning System originally designed for marine and military use.

[+julianh]

I has a Garmin GPSmap 60CSx and I bought it to get a better hight/elevation reading, but when I start my GPS it often show wrong elevation. I know that I must calibrate the altimeter, but if I calibrate it to (let say) 62 meter it dose change without the GPS is moving.

 

I did a test today and calibrated the altimeter to 62m, but after one hour the revelation eading was 68m. when I did the first test the altimeter setup was set to, "Auto Calibration = off" and "Variable Elevation". Same thing happens with the configuration set to, "Auto Calibration = off" and "Fixed Elevation", but when I had "fixed elevation" it just jumps around 59 to 65 meter.

 

So how shall I calibrate the altimeter to get a god relation reading and what dose the "fixed elevation" settings do? It maybe sounds like a dumb question, but my elevation is changing even I´m not move the GPS and the the altimeter seting is set to Fixed Elevation.

 

P.S Sorry for my bad spelling.

 

EDIT: Also, if I calibrate the altimeter to 62 meter and then go in to look at the compass the altimeter jumps to 66 meter when I return. Can it be so that my GPS is broken?

1. Turn Auto-Calibration ON (NOT off), and set to "Variable Elevation" for normal use.

 

2. At the start of each day, manually calibrate the barometric elevation. Preferably, enter the known elevation (if you know your current elevation - most of my days start at home, at 50 metres above sea level - or by reading off a topo map, or similar), or enter the known barometer pressure (the local met bureau might have real-time barometer pressure for your location on the internet), or if all else fails, calibrate to the GPS elevation if you have no other means of identifying your current elevation (but get a GOOD 3D fix first!)

 

3. With auto-calibration turned on, and your GPSr left on all day, you should get a good quality elevation reading all day long. I usually get plus or minus 5 metres all day on my Summit HC, plus or minus 10 metres under the worst conditions. I don't know of any consumer GPSr which will match that performance using GPS elevation alone.

 

No you can't get the elevation profile to show you the GPS elevation. You can only get an instantaneous reading of GPS elevation on the satellite page. (Yes, it would be nice if Garmin would give you the option, but they don't. Please don't blame me, or imply that I am apologist for Garmin! )

 

Once you have calibrated the barometric altimeter, and have auto-calibration turned on, you may see the apparent elevation drift slowly even when you are standing still, as it continuously re-calibrates itself against the GPS elevation. However, this effect should be very slow - maybe 2 or 3 metres in an hour or so, but after and hour or so, it will typically start drifting back in the other direction, so the displayed elevation will generally oscillate around the true elevation with an amplitude of just a couple of metres, and a period of a couple of hours. (Actual drift amplitude and period you will see will depend on the ever-changing satellite configuration at your current location.)

 

"Fixed Elevation" mode lets you use the unit as a very sensitive barometer at a fixed location. In this mode, the unit assumes your elevation stays fixed, so all pressure changes it sees must be due to barometer pressure changes. For normal "roaming" use, you use "Variable Elevation" mode, and the unit assumes that the primary driver of pressure changes is due to changes in your elevation. With Auto-Calibration turned on, the unit will use the GPS elevation as a tool to continuously recalibrate the barometer to allow for changes in both elevation and barometer pressure. (Yes, I know it sounds like Black Magic, and there are forum users who will tell you it is, but I don't believe most of them have actually used a properly set-up Garmin HS series GPSr. It really does work!)

 

Hope this helps.

 

(Sorry, Team CowboyPapa - you didn't think I would let you get the last word, did you? )

Edited April 18, 2008 by julianh