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Small coil for gear teeth count

Kumar
Intellectual 305 points

Hi, I am working on the prototype of Gear teeth count. My gear thickness is 2-3mm and the distance between consecutive teeth is 10mm. Is it possible to use a coil of diameter 6mm? If I use wire wound as a coil, what are the necessary settings I need to do other than RP_MAX and RP_Min. I mean any frequency settings in LDC is necessary? Can I use series Inductance if my wire wound have less Inductance? what is the normal range of Series Inductance?

Thanks,

Naveen

  • 0
    TI__Genius 14270 points

    Hi Naveen,

    The short answer is what you want to do looks reasonable, but let's make sure that you are good to go. First, what is the number of gear teeth per second? You will need to configure the LDC1000 sensor frequency so that it can support a sample rate >3x the number of gear teeth per second. 

    For example, if we have gear with18 teeth that rotates at 1000rpm, then there are 300 teeth per second, and we need to sample at least 0.9ksps to sample the gear teeth. 

    A higher oversample factor (5x or more is recommended), so for the example above 1.5ksps is recommended.

    There are two Analog Wire blog posts that should help you with the sensor characteristics:

    http://e2e.ti.com/blogs_/b/analogwire/archive/2014/06/10/inductive-sensing-how-to-use-a-tiny-2mm-pcb-inductor-as-a-sensor.aspx

    and

    http://e2e.ti.com/blogs_/b/analogwire/archive/2014/11/21/inductive-sensing-sensor-frequency-constraints.aspx

    Regards,

    Chris O

  • 0 in reply to Chris Oberhauser66
    Intellectual 305 points

    It is awesome for my application. Thanks Chris.

    Regards,

    Naveen

  • 0 in reply to Kumar
    TI__Genius 14270 points

    Glad to help. We're always here if you need us.

    Regards,

    Chris O

  • 0 in reply to Chris Oberhauser66
    Intellectual 305 points

    Thanks Chris,

    I have two more question. If I used coil in a stainless steel enclosure what will happen? If I am exposed coil up to 200 degree Celsius what happens to the proximity response?

    My observation is even Magnetic field lines won't cross the steel of thickness 2mm. So how can I make a coil which can work in High temperature or how can I shield the coil from high temperature. I am using a coil on ferrite core.

    Any suggestions are appreciated.

  • 0 in reply to Kumar
    TI__Genius 14270 points

    I assume that the enclosure is not moving relative to the sensor, and only the target is moving. If the sensor coil is inside a stainless steel enclosure, then the effect will usually be the effective RP (parasitic loss) of the sensor will be lower. As long as the RP is not below the minimum level of the LDC, you will be ok on that point.

    As for the high temperature, the 200degrees may be too high for your ferrite - the permeabilty may fall off below 200degrees. You will need to select an appropriate ferrite material.

    Also, make sure that the sensor capacitor can handle the temperature -  C0G grade caps are typically rated only up to 150C. You may need a Silicon capacitor to handle 200C. The capacitor should be near the inductor for best performance. The actual inductor will be fine.

    The LDC should be placed remotely to avoid exceeding its temperature rating.

    Regards,

    ChrisO

  • 0 in reply to Chris Oberhauser66
    Intellectual 305 points
    Hello Chris.
    your right. It is little tricky and hard to play with sensitivity and Rp if I start using steel plate cover to the sensor. Now I am thinking to use Epoxy which can cover the sensor. Epoxy resins can tolerate the temperature up to 500 degree Celsius. But, I am not sure Epoxy resins can withstand 250 bars of pressure? What is your opinion. Epoxy is a good Idea?


    Naveen
  • 0 in reply to Kumar
    TI__Genius 14270 points
    Hi Kumar,
    Unfortunately, I do not have an expertise in epoxy characteristics. Loctite manufactures something that may meet your needs at http://www.loctiteproducts.com/p/epxy_weld_t/overview/Loctite-Epoxy-Weld-Bonding-Compound.htm, although you will need to assess if it meets your requirements. Note that this is not an endorsement or based on any specific information we have on the Loctite product.
    Regards,ChrisO
  • 0 in reply to Chris Oberhauser66
    Intellectual 305 points
    Yeah I can Understand.

    Thanks for your help.

    Naveen
  • 0 in reply to Kumar
    TI__Expert 6550 points
    Naveen,

    Please let us know if you have any other questions.

    Best Regards,
    NatalliaH