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TMAG5173-Q1: Sensor Recommendation for 120-degree Rotary Motion

Egemen Aksoy
Intellectual 925 points
Part Number: TMAG5173-Q1
Other Parts Discussed in Thread: DRV5055, TMAG5253

Tool/software:

Hello,

I originally came across the TMAG5173-Q1 sensor while researching on the forum, but we are actually looking for a different sensor for another application. We need an absolute position sensor (preferably inductive, but Hall is also acceptable) for a 120-degree rotary motion.

Since we cannot place the IC exactly in the center, we are planning to implement an arc-shaped design similar to the one shown in the image. Could you recommend a suitable sensor for this purpose?

Due to mechanical constraints, the design should be in arc shape. The inner diameter is 20.5mm, outer diameter 29.5mm.

Additionally, for the arc structure, would it be possible to implement the mentioned application in this way?

Best regards.

  • 0
    TI__Mastermind 21250 points

    Egemen,

    If rotation is constrained to 120° then you have several options with magnetic sensing.  The most basic is to use a single 1D linear hall effect sensor, like DRV5055 or TMAG5253.  A rotating diametric magnet would produce a sinusoidal Z-component of the magnetic field when placed off-axis, like on the inductive sensing PCB shown above. Using less than 180° rotation means that careful installation of the source magnet would allow you to constrain the input to the most linear portion of the sine wave

    You should be able to normalize the output of the sensor and then use an arcsin or arccos calculation to resolve the absolute angle.

    Additionally, you could use TMAG5173, as you have referenced here.  In an off-axis position, you could pick one of the possible angle combinations XY,YZ, or ZX depending on placement and how well matched these components are.  Performing an arctangent function on the resulting sine and cosine outputs of the sensor would allow for absolute angle measurements without needing to give particular care to the magnet installation. If the magnet were installed at an arbitrary angle, you would still need to calibrate the zero position and store that angle offset in your MCU.

    Lastly, you have also correctly identified that inductive sensing is also capable of detecting the rotation angle using arc segment shaped coils. 

    I am happy to respond to any of your questions about implementing your design using magnetics, and I've looped in  to help you with particulars of the coil design if you prefer to investigate the inductive solution.

  • 0 in reply to Scott Bryson
    TI__Mastermind 44030 points

    Hi Egemen,

    The LDC5072 would be the inductive sensing device that could be used for this type of application.  Typically, customer applications use a full circle type of design, but an arc is also possible.  We have a tool that is able to help with designing the coils.  Unfortunately, I have seen that there is a bug with the tool where the arc designs are not generated properly, so you would need to do some manual design and layout for an arc coil.  You can find the tool below.

    https://www.ti.com/tool/LDC-DESIGN-TOOLS