• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 30 subscribers
  • Views 755 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMP91300: Coil Shape of the sensor

user4771603
Prodigy 75 points
Part Number: LMP91300


Hi, 

I have an area of 20x44mm  where I have to detect a target at 5mm distance.

The problem I have is when the target is present it will cover 40% of that area but cannot know the position due vibrations. I mean that the target could be anywhere in the area of detection.

In this situation what coil shape do you recommend?

- Racetrack spiral coil. (20x44mm)

- Rectangular coil. (20x44mm)

- 2 Circular coils in series drived by the same LMP91300. (2x 19mm diameter)

- 2 Circular coils drived by different LMP91300. I guess it would be difficult to make them work at different frequencies to avoid interferences between sensors (I have to work below 800KHz). Do you know any rule of thumb about the gap of frequency between sensors to avoid interferences. Also I think itwould be possible to have a "blind" spot between coils. 

- Any other suggestion?

  • 0
    TI__Genius 13335 points
    Hello,
    Typically when the target covers less than 100% of the coil we see a sensitivity decrease. For more info on this effect please refer to the following blog post: e2e.ti.com/.../inductive-sensing-target-size-matters
    If you split the area up into 2 coils driven by 2 LMP91300 devices then this could work, but you would want at least 1 coil diameter of separation between them or drive them alternately so that both are not on at the same time to avoid interference. The alternative is to operate them both at different frequencies of >10% difference. The concern you may see is that operating at such low frequencies to take advantage of the Rp shift outlined in the Target Design application note then having 2 different fundamental frequencies may result in a different frequency shift. If you are able to calibrate both devices at temperature then this may be ok. I just wanted to point this out if you decide to go this route.
    Regards,
    Luke