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Original question:

[FAQ] Inductive sensing FAQ - Frequently asked questions

Inductive sensing - long distance

Pasquale De Sando1
Prodigy 50 points
Other Parts Discussed in Thread: LDC1612, LDC1614

Hi All,

I need to implement a contactless position sensor, to measure absolute linear position over a 45cm stroke, accuracy of ~1mm.

At first glance, an Inductive to Digital Converter (like the LDC1612) coupled with a rectangular streched coil looks a good candidate, however, looking at the "Inductive sensing FAQ" section in the E2E support forum this solution is not recommended for distances greather than 10cm.

I was wondering if the 10cm limitation can somehow be overcomed.

what's the rationale behind that maximum value and can it be overcomed, playing with the coil geometry?

is there any other technique more suitable for contactless linear position measurements over a such long distance (45-50cm) ?

Thanks in advance

  • 0
    TI__Expert 7589 points

    Hello,

    Thanks for taking the time to read the Inductive sensors FAQs. The 10 cm limitation is primarily due to the limitations of our devices. The inductive sensing devices are really meant for applications that can measure submicron to <10 cm. The primary reason being a larger distance would require a larger coil that would indicate larger inductance which implies lower frequency.  Our inductive sensing cannot drive lower frequencies and is designed to work with PCB coils this is the primary reason for not supporting large distances. 

    For longer distances range which is over 45cm I recommend our ultrasonic device or Hall sensor devices in our portfolio. Here is the link to the Ultrasonics FAQ https://e2e.ti.com/support/sensors/f/1023/t/640810 and Here is our link to Hall Sensing FAQs https://e2e.ti.com/support/sensors/f/1023/t/355909

  • 0 in reply to Arjun_Prakash
    TI__Expert 7589 points

    Hello User, 

    I haven't heard from you in a while and I am closing this thread. If you have more questions please do start another thread. 

  • 0 in reply to Arjun_Prakash
    Prodigy 50 points

    Hi Arjun,

    If the length is limited to approx 10cm, do you think it's feasible to take advantage of the multichannel configuration of the LDC1614 and split the 45cm coil into several smaller coils?

    In this case I would drive just one coil per time, so I shouldn't be too much concerned about the coupling between coils and the condition when the target is transitioning between two consecutive coils.

    Do you think this might be a fairly reasonable approach?

    Thanks

  • 0 in reply to Pasquale De Sando1
    TI__Expert 7589 points

    Hello User,

    Your idea sounds great! however the part is not designed to work with 1 large coil driven by 4 independent channels as the the characteristics of the part is to drive 4 independent coils. Based on your approach I am unable to tell you if this would work in your application. My recommendation would be to use an alternative technology like optical , Hall sensing or Ultrasonic.  

  • 0 in reply to Arjun_Prakash
    Prodigy 50 points

    Hi Arjun,

    I'm not saying that I want to drive one large coil using the four drivers.

    I'm saying that I want to replace one large coil (45cm long) with four independent coils (12.5cm), located along the axes where I have to sense the absolute position of the target.

    This means that I would need to drive four independent coils in multichannel configuration, with one coil at a time energized, and get the position of the target respect to the coils.

     

    I agree with the fact that I could consider an alternative technology; I'm already considering the AMR sensors however I would like to explore also this option before give up.

    Thanks

    Thanks

    Pasquale

  • 0 in reply to Pasquale De Sando1
    TI__Expert 7589 points

    Hi Pasquale,

    I understand. However one caution with driving 4 coils would be that care should be taken such that the 4 coils are isolated such that the eddy current dont get coupled into adjacent coils. As long as they are designed such that there is little to no interaction between coils. Take a look at our Inductive Sensing Faqs for more information on design tolls and target design.