Repetitive of current data fr AWAC

Hi,

Anyone ever encounter this problem of repetitive of current data collected in the AWAC 600kHz? Please view the attached pdf for more details. It seems like at every hour interval, the first and second readings for speed and direction appeared to be the same. Please advice.

Harum_s

Hi Harum,

What you are seeing here is that one current profile (the second of the two) is not being made.  This is because the AWAC does not perform a current profile if it is scheduled to make a wave burst measurement.  Since the AWAC does not perform both measurements at the same time the data from the first profile is output to file so that there is a uniform measurement interval in the file.

There is another case in the forum under Waves covering this point:
Wave and profile intervals

If the results that you are showing are generated by the AWAC software's data conversion function, then you will see that there is a check box that says "interpolate profiles" you may want to consider using this also.  Choice is your of course.

regards,
Torstein

Torstein,

Thanks for the information. Kindly have a look at the attached snapshot picture of the compass calibration for the AWAC 1MHz (N5024). Is the compass still in working condition since it didn't formed a perfect circle during the test? Should I update it? Thanks.

Harum_s

Torstein,

Thanks for the information. Kindly have a look at the attached snapshot picture of the compass calibration for the AWAC 1MHz (N5024). Is the compass still in working condition since it didn't formed a perfect circle? Should I update it? Thanks.

Harum_s

Hi Harum,

Torstein is away this week.  Your compass calibration looks fine.  The shape of the circle is controlled by the magnetic field near the AWAC.  This is what the calibration routine corrects for.  

Best regards,
Eric
eric@nortekusa.com

Hi Harum,

I would like to elaborate a little on what Eric wrote.

The compass is in working condition, the reason why it did not form a perfect circle is that the data is distorted due to a soft iron effect. Soft iron effects come from interaction between the earth's magnetic field and magnetically soft materials near the compass.

Hard iron effect on the other hand, come from permanent magnets or magnetised iron or steel that have a fixed position relative to the compass. Hard iron effect will offset the calibration data but the shape will still be circular. Our compass calibration routine fully corrects for hard iron effects as it centers the compass data around origin.

In your case, centering the data will improve the accuracy, hence it is a good idea to choose update. Ideally, you should try to reduce soft iron effect if you want the best accuracy. It is hard to say what kind of errors you can expect when looking at your calibration data but with some quick simulations my guess would be an error around 5 degrees (maximum). This assumes that you chose update so that the data was centered around origin.

Best regards,
Sven Nylund