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Metal Target Considerations

Kyle Reid
Prodigy 30 points

Hi,

I want to measure linear displacement of a rack in a rotary to linear actuator.  The rack is made of PH13-8Mo SS and I want to put a raised triangular feature on the top of it as pictured below.

The question I have are:

1. Will the metal behind the red triangle interfere with the measurement? 

2. What material should the red triangle be made out of/ could it be made out of the same material as the rack?

3. If the answer to #1 is yes could the the red triangle protrude in the z direction enough to not have the metal behind it interfere with the measurement?

Thanks in advance for the help.

  • 0
    TI__Expert 6550 points

    Hello Kyle,

    1. Yes, it will. The question here is how much the interferance will be and if you are able to get decent data. I have produced something like that in the lab, but I separated the triangle from the metal via an acrilic block. What is the thickness of the triangle?

    2. Any conductive material such as aluminum, copper, or steel.

    3. The thickest part of the triangle can cover the metal completely if the thickness is 3 times the skin depth. In the thin part (leftmost corner) of the triangle, you will see the metal behind it. Is there a way you could separate the two via a non - conductive material (plastic, acrilic, anything that doesnt pass the magnetic field through)?

    Best Regards,

    Natallia Holubeva

  • 0 in reply to Natallia Holubeva1
    Prodigy 30 points

    Natallia,

    Thank you for the quick response.  It sounds like the protruding metal triangle from the metal block might be more trouble than it's worth.  What if we milled a rectangular hole in the rack and then epoxied in a piece of circuit board with the triangle as a "trace" on the top layer of the board?  Would we need to worry about the metal around the board?  Another concern might be the location of this rack, basically assume it is in a metal box i.e. surrounded on all sides by metal.  Would that metal interfere, or is the magnetic field generated by the coil concentrated enough that it only affect what it is pointed directly at?

    Thanks,

    Kyle

  • 0 in reply to Kyle Reid
    TI__Expert 6550 points

    Hello Kyle,

    Please note that the field is 3-directional. The rule of a thumb is to make the coil the same size as the target. If your target is a triange, you would choose the diameter of your coil close to the max width of the triangle. The concern is when the width of the triange gets narrow, you will see the metal behind it unless you isolate the two with a non-conductive material.

    Best Regards,

    Natallia Holubeva