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Co-axial position sensor design?

Peter Clark25
Prodigy 110 points

We want to incorporate a position sensor in a hydraulic clamp, with a travel of about 60mm. Our mechanical designer wants to have a fixed, wire-wound coil about 15mm diameter by 5mm long. A tapered rod, attached to the moving piston, would pass through the centre of the coil. Is such an arrangement feasible using an LDC?

Kind regards,

Peter Clark.

  • 0
    TI__Genius 14270 points
    Hello Peter,

    I assume that the tapered rod is a conductive material. If so, then yes, you have a feasible design, if your intention is to measure the travel of the rod into the coil.

    Would it be possible for you to post an image of your desired system, just in case I envisioned something different than you?

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Prodigy 110 points

    Hello Chris,

    Here's a draft clamp position sensor, proposed by our mechanical designer. Is it likely to work, with all the metal in the vicinity?

    Regards,

    Peter.

    Position Sensor Assembly - Rev DRAFT 1.pdf

  • 0 in reply to Peter Clark25
    TI__Genius 13650 points

    Hello Peter,

    Metal in the vicinity will present itself as a fixed offset and a reduction in dynamic range. It is often still possible to design systems with it as long as achieved system accuracy is sufficient and the interfering metal is in a known position, 

    However, your diagram suggests that you are trying to sense an object that is approximately 1 coil diameter away through a layer of 2mm bronze and 2mm SS316, while additional interfering metal surrounds the coil (please correct me if I misunderstood the drawing).

    Even  at low sensor oscillation frequencies that result in deeper metal penetration, I do not expect the ac magnetic field of the coil to change sufficiently during movement of the taper to detect its position. 

    Some information on sensing through metal is in the inductive sensing FAQ (question What are the general guidelines for sensing a target through metal?)