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LDC1614: Relationship between inductance and measurement resolution

user6188424
Prodigy 160 points
Part Number: LDC1614

I have a question about LDC1614.

As the coil diameter increases (the number of turns increases), the inductance L increases,

but the detected frequency fsensor will decrease.

In that case, Is the measurement resolution lower as inductance increases?

In order to increase the measurement resolution,

should the inductance be as low as possible (with a smaller coil diameter) within the detection frequency range (up to 10 MHz)?

Also, could tell me the advantages of large inductance (large coil diameter)?

  • 0
    TI__Genius 17440 points

    Hello,

    The benefits of a larger sensing coil far outweigh any disadvantages of increased inductance. A larger sensor increases the sensing range and resolution. Further, a lower sensor frequency does not always translate to lower resolution. The optimal sensor frequency range is in the upper KHz to low MHz. 

    I recommend this application note for more information:Optimizing L Measurement Resolution for the LDC161x and LDC1101

    I also recommend reading through the FAQ linked below, especially LDC Sensor Design, which discusses the benefits of larger sensing coils.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 160 points

    thank you for your answer.

    Could you teach me with reference to your answer(“A larger sensor increases the sensing range and resolution.”).

    Is it correct with the following recognition?

    ・the detection range increases because of the absolute value of the magnetic field increases with the coil diameter is large.

    ・the resolution improved because of the magnetic field change is larger for a certain distance with the coil diameter is large.

    If the strength of the magnetic field affects the detection range and resolution, will it affect not only the coil diameter but also a number of turns and drive current?

    I want to know the parameters that affect the inductance for designing.

    Could teach me ｗhat is the equation for the inductance parameter due to changes in distance?

    Best regards.

  • 0 in reply to user6188424
    TI__Genius 17440 points

    Hello,

    It is not the strength of the magnetic field that affects the resolution and sensitivity; it is how far the magnetic field propagates in spaces, which is dependent upon the size of the coil. Because of this, the drive current also will not affect the sensing range (though there are optimal drive current settings, see here for more details).

    The number of turns will not affect the resolution nor the sensing distance, but the location of the turns can. The coil should have turns directly under the moving target. For example, in button applications the target movement is primarily at the center of the coil. In this case it is important to have turns extending all the way to the center of the coil, though we do not recommend using many inner turns for other applications.

    The equation for the changes in inductance is quite complicated. We use the LDC Tools Excel calculator to estimate it or an open source simulation tool called FEMM for more accurate calculations. However, all coils have extremely similar responses, so you should be able to use the graphs to guide general understanding. I recommend reading section 2.4 of LDC Sensor Design, which discusses many of your questions and includes the graphs I mentioned.

    Best Regards,