Duration for valid compass data  

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Edwin
(@edwin)
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21/12/2015 2:10 pm  

Hey!

I was wondering how long the GPSlogger would provide valid compass (and other) data without calibration and how sensitive is the compass for iron?
I have GPSlogger data from a month on a ship and the compass does not show reliable data (I checked it with log of the ship).
The values for the x, y and z axis for the compass are weird. We did do a calibration a couple of days ago, outside, after which the apparatus seemed to work, but afterwards we turned it of and again the data was incorrect.

Is it also normal that the device needs to be calibrated each time that you re-start it? That seems to be the case with ours.

I would be delighted if anyone could answer these questions!

Edwin


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21/12/2015 2:31 pm  

The digital compass that we use is similar to those of todays smart phones. So the "how to use" is simply the same:
It is affected by magnetic waves, radio waves and other stuff from the outside world. This may result in the compass not being accurate on different locations., because the conditions around you change.
Simply said, if you calibrate the compass before use, you get a more accurate result.
If you do not calibrate that often the compass may get less and less accurate, especially if you change locations alot.

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Edwin
(@edwin)
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21/12/2015 4:23 pm  

Would you recommend calibrating the GPS logger each day considering the fact that this GPS logger is on a ship with slow course corrections, radar and a lot of metal?
Or is the GPSlogger not suited for this task?
The problem is also that the compass does only deliver a heading between 340 and 360 degrees for headings of which we know that were completed different (170 and 050 degrees).


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22/12/2015 8:01 am  

In that case you should calibrate it as often as possible.
But i dont understand you heading problem, could you pleae tell us the problem more detailed?

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Edwin
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22/12/2015 9:02 am  

For the background information:
We mounted the GPSlogger on the railing of a ship, were it was send on a trip to Svalbard. It was send to monitor the heading and tilt in various directions.
The problem with the heading is that the compass only delivers headings between 340 and 360. I processed the raw data (the x-, y- and z-values) with the Aaronia GPS logger programming guide, which only yields the headings of 340 to 360 degrees, while we have headings from the ship own compass for certain time periods to check if our GPS logger worked. We know therefore that for a heading of 171 (ships compass) we find a heading of on average 350 for the GPS logger.
I checked the programming stuff again with a test run after calibration and it should be oke and the tiltfactor was incorporated.
Therefore, the x, y and z-values ought to be wrong. X-axis does only range between -50 and +50, the Y-axis does range between -300 and -600 and the z-axis ranges between -1000 and -1100.
Also, for certain headings, the offset shown in the x, y and z axis are not consistent.


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22/12/2015 9:24 am  

If you mount the unit to a massive iron railing it for sure will not work corectly. Keep it away from any iron parts as far as possible, DONT use iron made screws/mountings etc. to mount it.

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Edwin
(@edwin)
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22/12/2015 9:40 am  

Oke, that explains a lot. The GPSlogger was situated in a plastic box and placed several cm's above the railing, but on a ship it is hard to gain more distance than een meter from iron parts. So then for the future we should probably find a compass that is the least effected by interference from iron!


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22/12/2015 10:05 am  

With 1m distance it should work perfect (even far below that) but just some cm is a problem...
I dont think you we finde a better working digital unit. They all face this problem with near by iron.

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