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DRV5021: Can we distinguish between 4mm and 5mm

John Griffith
Mastermind 21769 points
Part Number: DRV5021

Hello,

I have a customer that is looking for a way to sense between two states (digital output), where one state the magnet is 4mm above the top of the device and the other state where the magnet is 5mm above the top of the state. Unfortunately the physical dimensions seem to be fairly set but both the magnet and the device are still to be determined. 

Watching the precision labs video on the topic you would want BOPmax<B(D1) and BRPmin>B(D2). Looking at the difference in distances and the spread of the thresholds this looks to not be possible. A couple questions:

  1. Is it possible to use any of the hall switches with set thresholds knowing that the magnet has not yet be decided on?
  2. If that is not possible, would something like an analog hall sensor with a comparator with a customer threshold work?
  3. Any other ideas for how to handle this situation?

Thanks!

John

  • 0
    TI__Mastermind 22385 points

    Hey John,

    Great to hear from you! 

    1. Possibly. Typically, the magnet is going to dictate the points at which you operate and release, but you could potentially look at some options for these sensitivities and try a variety of magnet grades and sizes to see if some combination could work. For such a tight spacing, you may want to look at some weaker alternatives, such as ferrite, as this will operate much higher on the B curve and the distance needed to release will be much smaller. There's some great information about this in this app note. That said, a 

    2. Yes, you should definitely be able to solve the problem using this method. 

    3. I need to understand the system a bit more to be able to help here.

    - Does the magnet have to approach the sensor head on? Is there a physical limitation on the size of the magnet?

    - Are the 4mm and 5mm designations tightly toleranced? Ie, is it okay if the device trips prior to 4mm, but by 4mm is a must, or do you need it to be precisely 4mm?

  • 0 in reply to Carolus Andrews
    TI__Mastermind 21769 points

    Hi Carolus,

    Thanks for the detailed response and sorry for the delay in following up. Since there are some customer details in the response I will take this offline via email. 

    John