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TMAG5170-Q1: Hall sensor unstable raw magnetic values

Aditya Barve
Prodigy 60 points
Part Number: TMAG5170-Q1

Hello, 

We are currently using TMAG5170-Q1 for an automotive application. 

1. We observe that though the magnet is placed steady over the sensor, the x, y, and z magnetic field readings fluctuate. 

     Attached is the snapshot of the configuration of the sensor . 

2. Also, when there is no magnet placed in the vicinity of the sensor, the x, y, z sensor values fluctuate over the full range starting from 0 - 65536 (both negative and positive data is interpreted)

   

Please let us know how these readings can be stabilized to get steady magnetic field values. 

Magnet Details:

Material: N35H

Shape: Rectangle

Thank you,

Aditya

  • 0
    TI__Genius 15290 points

    Aditya,

    There is some input referred noise which is expected in any measurement. 

    You can reduce the observed noise by increasing the averaging setting in DEVICE_CONFIG.  Currently you have 2x averaging enabled, but the device will support up to 32x.

    Thanks,

    Scott

  • 0 in reply to Scott Bryson
    Prodigy 60 points

    Hi Scott,

    We observe the fluctuations in x, y, z mT raw values, with constant magnetic field with averaging set to 32x. 

    Though we see variations in x, y z raw values, the angle value read from the sensor is stable. 

    We need to understand the reason for this behavior, and also suggest some way where we can test the raw values of the sensor against a reference so that the actual mT value can be related with sensor x, y z, readings.

    Pleas also have a look at the magnet details,

    Magnet material: N35H

    Magnet shape: Rectangle.

    Thank you

    -Aditya

  • 0 in reply to Aditya Barve
    TI__Mastermind 19640 points

    Hello Aditya,

    Scott is currently out of office due to a holiday in the US, he will be back in office on Wednesday and review your response then. We appreciate your patience!

    Best,

    Isaac

  • 0 in reply to Aditya Barve
    TI__Genius 15290 points

    Aditya, 

    Can you quantify or otherwise provide some description of the fluctuations you observe?  Even at 32x averaging, there will be some input referred noise that will be observed.  Can you also describe the motion you are tracking?  Is it rotation with a rectangular magnet?

  • 0 in reply to Scott Bryson
    Prodigy 60 points

    Hi Scott, 

    Sorry for the delay. 

    Below are the x,y and z mT values read from the sensor, when the magnet was kept stationary over it. 

    Configuration: CONV_AVG set to 32x

    x, t, z ranges set to 100mT. Formula used for calculation as per data sheet. 

    (xRaw/65536)*(2*magnetic range) ==> (xRaw/65536)*(2*100)

    x axis (min: 42  max: 112)

    mT: min0.128mT  and max: 0.341mT

    y axis (min:-7800 max: -7780)

    mT: (-23.8mT min and -23.74mT max)

    z axis (min:1979  max:1997 )

    mT : (6.039 mT min and 6.094 mT max)

     .

    Please let me know, if any other details are required.

    Thank you,

    Aditya

  • 0 in reply to Aditya Barve
    TI__Genius 15290 points

    Aditya,

    Thank you for providing this data.  This looks like it is primarily just the input referred noise of the device.  In your data, the X axis appears to have the largest variance of about 213 uT peak to peak.  The specified value for noise is in RMS, which represents a 1 sigma value.  The datasheet reports this for the +/-50 mT range at room temperature and 32x averaging to have a maximum value of 34 uT.  Multiplying by 6.6 will give us a 99.9% peak to peak value for noise at approximately 224.4 uT.  While I would have anticipated this to fall closer in line with the result measured on the Y axis, this does appear to be within specification.  I would anticipate though if you tried with another device you would likely see lower noise in this axis, since the typical RMS value for noise in either X or Y is 24 uT (158.4 mT peak to peak).

    Thanks,

    Scott