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DRV425EVM: Use for Geophysical Surveys

Jim Major
Prodigy 10 points
Part Number: DRV425EVM
Other Parts Discussed in Thread: DRV425, TIDA-00463

I am researching methods for building a magnetometer for conducting geophysical surveys to detect buried ferrous objects such as pipes or cultural items such as iron tools.  These items can be detected using a conventional proton precession or fluxgate magnetometers and have field strengths which are typically greater than the earth magnetic field by 500 to 25,000 nano Teslas (i.e. 50,500 to 75,000 nT total). For conducting surveys, logging of the total magnetic field at around 50 to 200 readings per second would be ideal.  Also, averaging of readings measured at higher rates (i.e., 1000 Hz averaging 5 readings to arrive at 200 averaged readings per second) to hopefully reduce noise would be helpful.  The sensor would be placed around 2 feet above the ground surface for collecting measurements while moving the instrument around the areas of interest.  

Is the DRV425 sensor capable of sensing sizable ferrous objects 2 feet above the ground at total field magnetic field strengths of 50,500 nT and at 200 Hz sampling rate?

If I read the information correctly, the TIDA-00463 module would use 2 DRV425, and is equipped with instrument amplifiers and analog to digital converters (ADC).  Does TI plan to build a TIDA-00463 or similar item?  

If not, would the configuration of the TIDA-00463 work as a geophysical instrument sensor for use as described in my first question and are the specified amplifiers and ADCs sufficient to reduce noise and increase the sensitivity or are better components available?

Thanks

Jim Major

  • 0
    TI__Mastermind 30750 points

    Hello Jim,

    The DRV425 has a maximum full scale of ~2mT so it may be to small of a scale for what you are trying to measure.  But if you use the DRV425 for the lower range you will be limited by noise.  Assuming the 200Hz the noise will be about 200nT from the DRV425.  See this E2E post

    The TIDA-00463 does use 2 DRV425 but we do not plan on building the TIDA-00463.  You can download the design files if you would like.

    The noise will be limited by your filtering and the speed you are willing to measure.  The range of the field is the biggest issue in my opinion.  Unless you can live with the DRV425 only measuring below 2mT.  Then we can dig into the other components.

  • 0
    Prodigy 10 points

    Javier, thanks for the quick reply to my question.  The maximum measurement that I think that I would ever encounter using the magnetometer would be 1 milli Tesla.  Would the TIDA-0063 design lower the noise below 200 nano Teslas?

  • +1 in reply to Jim Major
    TI__Mastermind 30750 points

    Jim,

    From the noise analysis you would need to measure at 8Hz to get a peak to peak noise of 50nT.  The ADS124x can sample much less frequency so you could achieve this ideally. 

    For the differential measurement you now would have to measure the two DRV425 at the slow rate if you would like to measure a differential field as the TIDA-00463.  The noise will not be improved with differential measurements unless you are trying to remove external influence noise.  The noise I have been describing is noise from the sensor itself.  If you do need to do a differential measurement I would measure both sensors at a higher frequency and average the difference to avoid issues with the external interference.