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LDC1612: Using a ferrite target for linear position sensing

Matthias Meier1
Prodigy 180 points
Part Number: LDC1612

Hi,

I've simulated a linear position sensing configuration consisting of a stretched PCB sensor coil and a longitudinally moving target (as described in the app notes) in a 3D field solver and found that I get a significantly greater change of inductance over the length of displacement when I use a ferrite material for the target than with a highly conductive (non-ferrous) solid metal alloy like brass.  I do understand the different causes for the inductance change (high permeability in case of the ferrite vs. mutual inductance due to eddy currents).  As long as I don't mind what's causing the inductance change and all I want is to maximize resolution for the same size coil and target, the ferrite would be the more attractive choice.  Any reasons not to use a ferrite target?

Thanks!

Matthias 

  • 0
    TI__Genius 13335 points
    Hello Maathias,
    Which 3D field solver are you using? Does it have the ability to simulate temperature effects? I would be cautious about using ferrite targets instead of a conductive target for two main reasons. The first is that the ferrite material will likely have a temperature dependent magnetic properties. This means that if the target is stationary and the temperature if fluctuating in the room, then you could potentially see a difference in response. You would need a way to monitor the temperature in the room or have an additional sensor for calibration. The second is that the part-to-part consistency on ferrites is not well matched and the magnetic properties are not uniformly distributed across the material. This would again point towards some sort of calibration. If possible I would try to stick to a traditional conductive target and/or add additional sensor channels to the design to add some sort of compensation/correction factor.
    Regards,
    Luke