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LDC0851 how to get suitable design

na na78
Guru 16770 points
Other Parts Discussed in Thread: LDC0851EVM, LDCCOILEVM, LDC0851

Hi

We assume the following system.

CASE:1

CASE:2

The purpose of this system is just to detect the metal board.

Distance between target metal board and sensor is about 3cm ～5cm.

So, we need information how to design coil.  Could you please advise us?

1. What do you think which coil placement case is better, case1 or case2?

2. We have LDC0851EVM and LDCCOILEVM. So, we want to start evaluation.

What do you think which coil size and capacitance should be chosen?

3. We can use LDC calculation tool (excel sheet).
If possible, could you feedback how to design coils as example?

Best Regards

  • 0
    TI__Mastermind 41310 points
    na na78,

    I have moved your post to the Inductive sensing forum.
  • 0
    TI__Intellectual 2725 points
    Hello Na,
    Thank you for considering the LDC0851 for your application. Could you please provide me with the operating temperature range for the application?


    Regards,

    Varn Khanna,
    Applications Engineer, Sensor Signal Path,
    Silicon Valley Analog,
    Texas Instruments,
  • 0 in reply to Varn Khanna
    Guru 16770 points
    Hi Varn

    Thank you for your reply.

    The operating temp range is 25 degree to 40 degree (it is almost at room temperature).

    BestRegards
  • 0 in reply to na na78
    TI__Intellectual 2725 points

    Hello Na,

    That's perfect. This actually simplifies things a lot.

    Since you are already familiar with the LDC spreadsheet and Webench design tools, I can recommend the following configuration:

     

    You should design a spiral LSENSE sensor so it falls in the LDC0851’s design space, and calculate it’s inductance at the switching distance using the LDC Tools Spreadsheet, let’s call this value X.

    Once you have figured out X, design a much smaller coil with the inductance value of x which will be your LREF sensor. You can place the coils concentrically as in the picture above.

    Regards,

     

    Varn Khanna,

    Applications Engineer, Sensor Signal Path,

    Silicon Valley Analog,
    Texas Instruments,

  • 0 in reply to Varn Khanna
    Expert 1070 points
    Hi Varn,
    will this configuration really work? I believe that inductunces of those coils should be identical.

    Best regards,
    Igor Gorbounov
  • 0 in reply to Varn Khanna
    Guru 16770 points

    Hi Varn

    Thank you for your reply.

    Could you check our calculation results?

    ■For Lsense

    - Spiral inductor designer 

    -LDC0851 calc

    ■For Lreference

    - Spiral inductor designer 

    -LDC0851 calc

    BestRegards

  • 0 in reply to na na78
    TI__Intellectual 2725 points

    Hello Na,

    Please accept my sincere apologize for the delay in getting back to you. 

    Excellent work! I am glad you got good use out of our design tools.

    I think I didn't explain the reference sensor config well enough. You want the free space inductance of the REFERENCE sensor to be equal to the inductance of the SENSE sensor at the switching distance. So in this case, if you want to switch at 3cm away from a rough estimate you want the REFERENCE sensor inductance to be around 6uH. For 4 cm switching distance your reference inductance would be ~6.22uH.

    Could you also confirm how close does the metallic target get to the sensor?

    Regards,

    Varn.

  • 0 in reply to Varn Khanna
    Guru 16770 points
    Hi Varn

    Thank you for your reply.


    >Could you also confirm how close does the metallic target get to the sensor?
    I'm sorry I made a mistake. The answer for your question is 3cm-5cm. (It is closest target distance on spread sheet, isn't it?)
    So, we supposed that SENSE sensor switching distance is the closest distance between the sensor coil and the target.

    And I had additional question.
    If we start to design the configuration that you proposed in previous answer, how to get the design data?
    Can we use WEBENCH?

    BestRegards
  • 0 in reply to na na78
    TI__Genius 13650 points
    Hi Na Na,
    yes, you can use Webench coil designer to design the coils, such as the ones that Varn proposed: www.ti.com/.../inductive-sensing.page