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Optimal target choice

Bjornar
Prodigy 200 points

Hi

We are in the position to chose an optimal target for our distance sensing application.

For background please read my other two threads linked below.

We are testing different setups in the measureing in the range 1-15mm in sea water with custom coils ranging from 30-50mm with 2x115 to 2x125 turns.

We need to obtain the best resolution possible in our setup and we can also choose the target material as we please. We have been told that it is best to use the inductance measurement as it is less infected by temperature and that aluminium would be better to use than steel as it will give better results.

1) It is strange that the coil designer only has two types of stainless steel and copper as target alternatives when aluminium will give a better result. Do anyone have a good answer to this?

2) We need to have as good resolution as possible although space is a limitation so the coil and target cant be too big. What are your experiences with using different materials? I have calculated the skin depth of aluminium to be 38um, and I wonder if the rule of thimb when using copper also applies to aluminium, that one should at least have target thickness which is two times the skin depth? If so we would need appx. 76um or 0,076mm which is far thinner than what we would use.

Regards, Bjørnar

http://e2e.ti.com/support/data_converters/inductive-sensing/f/938/p/376492/1330500.aspx#1330500

http://e2e.ti.com/support/data_converters/inductive-sensing/f/938/p/377302/1329145.aspx#1329145

  • 0
    TI__Expert 6550 points

    Hello Bjonar,

    1. We are working on adding Al to the coil designer simulation tool. If you choose to use Al, you will get closer results simulating with Cu since Al and Cu have simular properties.

    2. In your mechanical setup, do you have anything placed behind your target? Skin depth follows Gaussian distibution. Thus, you will have better results if your target is 3 skin depth (or 3 sigma = 99.73% of total possible coverage). 1 skin depth would give you 68.27% coverage, and if there is nothing placed behind the target, I would not be very concerned about it.

    Best Regards,

    Natallia Holubeva