76csx Altitude/barometer Problem

[toddm]

Not sure if anyone has ran across this one but I was playing with the elevation plot today, for giggles to compare it to my suunto advisor.

 

I notice that if I set the 76csx to plot elevation, and calibrate it to a known altitude, in a few minutes the barometer goes to 0.00 and the unit quits reading elevation. Ambient pressure is still registering.

 

I'm not sure if this is a factor of the unit not being moving, so it's turnning the sensors off to conserve battery if the unit is not moving, or some other glitch, but I seem to remember my 76s would do this with no problems.

 

I'm running another test with the auto calibration off to see if that may be the issue.

[toddm]

It does appear to be related to the barometer. If I use the elevation plot with the auto calibration turned off, it appears to work fine. However the display still shows a barometer reading that is way way off.

 

For the first few minutes the barometer reads fine, but after that it tanks, right now it's readin 54.75pa (it seems to always tank at this value and will not change unless the unit is turned off and on) while ambient pressure is reading 980pa.

Edited April 2, 2006 by toddm

[+dhbaird]

It does appear to be related to the barometer. If I use the elevation plot with the auto calibration turned off, it appears to work fine. However the display still shows a barometer reading that is way way off.

 

For the first few minutes the barometer reads fine, but after that it tanks, right now it's readin 54.75pa (it seems to always tank at this value and will not change unless the unit is turned off and on) while ambient pressure is reading 980pa.

 

Can not tell you much from the limited experience with my 5 days of owning a 76csx, but so far the altimeter has been not as reliable as the one in my 76cs. Even after calibration it seems to be off by more than I would like.

 

Here's my recent tests. I walked to a local benchmark that has been recoverd and position adjusted both vertically and horizontally. I calibrated for altitude and then walked to the next benchmark (10 minute walk away) and checked it against my charts for the 5 benchmarks on my walking route. Even after just 10 minutes the new 76csx was off elevation by more than 8 feet. One time it was 26 feet.

 

With my prior 76cs, without calibration it was never more than 6-8 feet off on my initial BM and then after calibration was 2 - 3 feet or less. 10 minute walk to the next BM was within 2 feet. One time it was right on the money and stayed that way for all 5 BM's. I took readings on a defined point at my home right after calibration and when ever I turned on the 76cs as I was heading to the car for a geocaching outing I would check to see how close it was ... if it was more than 8 feet I would recalibrate. Only had to recal 2-3 times. Now with the new 76csx, each time I go out the door the elevation is off by 14 to 20 minimum.

 

This tells me that the sensor in the 76CSX has been changed somehow... or the algorithem for correcting the altitude in the auto-calibration mode is off.

 

I have yet to try the same test while shutting off the auto-calibration function on the altimeter. Will keep you posted.