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Measurement of material thickness and/or features

Ahmed Abasiry
Prodigy 45 points

Hello,

I was wondering if the LDC1000 is able to sense features (cutouts, channels) or irregularities (pits, holes, scale buildup) on the face of metal (mild steel). If so, what does the resolution depend on and what would be the maximum resolution that can be obtained?

I am looking to measure features with about 2 or 3mm in size. Is this possible?

Thanks and Regards,

  • 0
    TI__Genius 9300 points

    Hello,

    Just to make sure we are on the same page: you are going to scan the surface of the metal in search of these features, correct?

    I've run a few sims, presuming that the distance between the metal and the coil is constant. Here are the results.

    I've used 2mm dia coil (you will need small diameter coil to detect small features)

    With no surprise, it detects holes from ~1mm  an up. If a cutout is through, it acts just as a hole.

    It detects pits/channels, if the coil is sufficiently close to the metal (0.1mm in this case) or the pit is sufficiently large (2mm pit at 0.1mm away, or 4mm pit at 1mm away - it's a tradeoff.

    What kind of resolutions are you looking for?

  • 0 in reply to Evgeny Fomin
    TI__Intellectual 2065 points

    Please let us know if you still need help on this.

    Regards,
    Murali

  • 0 in reply to MS1291
    Prodigy 45 points

    Hello,
    I am resurrecting this thread again because a renewed interest in the project came up. I read your comment about the coil being physically small in size in order to detect small features. What about the inductance of the coil? Also, the type of coil (air core, PCB, ferrite..etc). Any suggestions?
    Thanks

  • 0 in reply to Ahmed Abasiry
    TI__Genius 13650 points

    Hi Ahmed,

    we now have an apps note that covers these topics in detail:   

  • 0 in reply to Ben Kasemsadeh
    Prodigy 45 points
    Hello Ben,
    Thanks for the reply. I did read this app note before, although useful, but it only seems to describe the behaviour of different types or inductors and calculating various other parameters. This is all assumes that the inductor has already been chosen, which is not the case. It does not, however, answer the very basic question of how to choose the physical size/type of the sensing inductor for a given target size. Or did I miss that?

    My application requires the measurement of:
    1- Features of ~ 2-3mm on a sheet of mild steel.
    2- The thickness of a sheet of mild steel up to ~22mm with a resolution of ~0.5mm

    Design criteria:
    1- It is not necessary that the same inductor be able to do both measurements, I could have two different sensors.
    2- I have the ability to keep the distance between the sensing coil and the target constant.

    Thanks..
  • 0 in reply to Ahmed Abasiry
    TI__Genius 13650 points
    Hi Ahmed,
    how would the coil be positioned? The LDC won't be able to see through 22mm steel, but if you are able to position the coil perpendicular to the steel plate, then you could use a stretched coil to sense thickness, as described in approach 2 of this apps note: www.ti.com/.../snoa931.pdf
    For prototype purpose, I think coil D or F from the reference coil EVM may work well for you: www.ti.com/.../ldccoilevm.
  • 0 in reply to Ben Kasemsadeh
    Prodigy 45 points

    Thank you Ben,

    I will order the coil EVM and try out the two you recommended.

    Cheers,

  • 0 in reply to Ahmed Abasiry
    TI__Genius 13650 points
    Hi Ahmed,
    great! Good luck with the evaluation.