compass maintenance

We have acquired an Aquadopp current profiler in 2004 . Since then we have used it just for a few times, and we never send the equipment to nortek for maintenance. In the last survey we have noticed a possible distortion in the velocities orientation. Do you think that this might be related malfunction of the internal compass? How long the internal compass can last without any distortion in the magnetic field?
thanks,
Ana

Dear Ana, the compass does not need recalibration.  Normal failure modes are of a kind where you get error messages (no data) so I doubt that this is the case.

I would recommend checking that the deployment frame you used is not magnetic.

Best regards,

Atle Lohrmann

Dear Atle,

Thanks for your reply. The equipment was deployed in a shallow water environment (seawater). After equipment retrieve, I have noticed that the sound speed was selected as fixed. the user specification for sound speed was by default 1525 m/s (equipment default). Following the suggestions in the nortek forum I had determined the true speed at each data point V_new = V_old * (c_new/c_old) . (variations are not significant).
Afterwards, when I plotted velocity east vs velocity north, the difference in magnitude between both velocities did not look ok (difference between north and east should be lower).Thus, I though that this could be related with any problem with the internal compass...

Meanwhile, I had performed another test with the adp, and the data look ok now. I am totally confused, because I cannot explain what happen with those data. I had already contact inquiry@nortek.no. I´ve been looking to the .hdr file containing the deployment description, in order to compare it to a previous survey, where data was fine. The only difference I had found was in the comments section. In the present survey to the System9 corresponds a 0 value, while in a previous survey to the System9 corresponds a 96 value. I am not familiar with the meaning of this system codes. Actually, I don’t know if this is this a problem and if is there any chance to solve it.

Best regards

Ana

    Hi Ana, I think that, when Atle was referring to deployment frame, he was trying to say that the solid base or structure on which you put and fixed the instrument do not generate a magnetic field. More information about this issue must be in 'Calibrating the Compass' in your User Manual.

Good luck.

Previously Ana Carrasco wrote:

Dear Atle,

Thanks for your reply. The equipment was deployed in a shallow water environment (seawater). After equipment retrieve, I have noticed that the sound speed was selected as fixed. the user specification for sound speed was by default 1525 m/s (equipment default). Following the suggestions in the nortek forum I had determined the true speed at each data point V_new = V_old * (c_new/c_old) . (variations are not significant).
Afterwards, when I plotted velocity east vs velocity north, the difference in magnitude between both velocities did not look ok (difference between north and east should be lower).Thus, I though that this could be related with any problem with the internal compass...

Meanwhile, I had performed another test with the adp, and the data look ok now. I am totally confused, because I cannot explain what happen with those data. I had already contact inquiry@nortek.no. I´ve been looking to the .hdr file containing the deployment description, in order to compare it to a previous survey, where data was fine. The only difference I had found was in the comments section. In the present survey to the System9 corresponds a 0 value, while in a previous survey to the System9 corresponds a 96 value. I am not familiar with the meaning of this system codes. Actually, I don’t know if this is this a problem and if is there any chance to solve it.

Best regards

Ana