problem of direction
Hello David,
I have a problem of direction.
We are in a river so we know the direction of curents. the main current are along the river.
But the ADCP don't say that. you can sea the Eco255_20220225094920 datas. We have south north current but if you watch where is the position you will sea that's impossible.
You can sea all my datas and I think all are wrong.
we put 40kg of steel anchor. The anchor is at 1m below the ADCP. Do you think is this? In the FAQ you give the commonly used anchor materials and there is the steel.
can we do an calibration of the compass?
What do you think?
Thank you very much
best regards
Tanguy
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Official comment
Hi Tanguy
This does appear to be a matter of interference on the compass. A mass of 40 kg of regular steel (which is highly magnetic) so close to the Eco is a likely source of the directional bias you are seeing. Was the same anchor and distance used for both your recent deployments?
I understand you would like to keep the mooring line between the anchor and Eco buoy to be as short as possible (e.g. 1 m or less), so in this case our recommendation is for you to switch to a non-magnetic anchor, like lead.
The Eco does not provide a compass calibration routine. However, even if it did, it would likely not help you much here, as 40 kg of steel is a lot of mass.
Comment actions -
Hello David,
I may have found what wasn't working. As we are on rivers we know the direction of the currents. The difference between what we know and the results is about +40 deg. The magnetic declination is -18.45 deg. Nor will there be a sign problem in your algorithm? Because if the algorithm takes +18.46 then the results would be +37 deg and that would be good.
can you check if there is a problem.
thank you very much
best regards
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Hello Tanguy
I know it might seem to be an algorithm issue, because 37° is close to what you see as a directional bias, but that's just a coincidence. The algorithm is correct. It's a simple subtraction calculation, so not hard to get it right. If it was wrong, then while that might make your data seem more along what you'd expect, there would be hundreds of other Eco users whose deployments would be wrong :-)
Take care,
-Dave
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Hello David,
I took measurements in an estuary.
I put you the figure on google earth. in red they are the directions given by the ADCP and in blue the real directions. The three to the north have 27 kilo steel weights (ouestADCP, milieu ADCP est ADCP). the one to the south has a concrete weight (ADCP béton).
the difference between the real directions and the measured ones is between +30° +40°, even with concrete.
can you explain what's going on?
thank you very much
Tanguy
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