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Detecting metal slug inside steel pipe.

cliven
Prodigy 70 points
Other Parts Discussed in Thread: LDC1612, LDC1101

I have an application that requires the ability to detect a moving ferrous metal slug as it moves past a cert point inside a ferromagnetic/steel pipe.  I have been attempting to solve this using a permanent magnet and coil as shown in the attachment but am having problems with the coil picking up the vibration of the slug against the inner wall of the pipe even when it is not in close proximity to the sensor (I'm assuming the PM is magnetizing the pipe). Also, there is not enough magnetic field inside the pipe to reliably detect the slug.  I would like to know if an inductive sensor would be a better option for this application.

drawing1.docx

  • 0
    TI__Genius 9300 points

    Hello,

    Could you please answer a few questions?

    1. slug dimensions?

    2. Slug speed?

    3. Thickness of the pipe walls?

    4. Can you wrap a coil around the pipe?

  • 0 in reply to Evgeny Fomin
    Prodigy 70 points

    Evgeny,

    Thanks for your reply.

    1. Slug dimensions can vary but generally are 1.9" diameter and 5" to 8" length.

    2. Speed also varies anywhere from 15 ft/s at the fastest to 0.5-1 ft/s at the slowest.

    3. Pipe walls are approximately 0.36" thick.

    4. Pipe diameter is 2.75"...could possibly wrap a coil around the pipe.

  • 0 in reply to cliven
    TI__Genius 14270 points
    You would need to design a sensor with a resonant frequency of 5kHz; the goal is to get the skin depth at the sensor frequency to be deeper than the pipe wall thickness. This frequency can be supported by the LDC1000 or LDC1612 (but not the LDC1101, which has a minimum sensor frequency of 500kHz).

    Regards,

    ChrisO