TMAG5273EVM: magnetic sensor Range / sensitivity

Madhav,

Thank you for reaching out with this design question.  Our devices which currently operate over SPI are TMAG5273 and TMAG5170.  These devices have three integrated sensors capable of detecting the field component in each X,Y,and Z axis.  Typical position sensing with these devices uses a permanent magnet to provide the input magnetic field.  The magnetic field diminishes quickly as range to the magnet increases.  This typically requires that the sensor is placed near the path of the moving magnet.  If the presence of the vehicle is able to influence the magnetic field of a stationary magnet (due to ferromagnetic materials such as steel), then it might be possible to detect the presence of a vehicle, but at large ranges, this would be very difficult.

Thanks,

Scott

Madhav,

The vehicle by itself would not be detectable.  The sensor would require some magnetic field, which the vehicle would then interfere with.  We have a calculator tool which might help you understand and estimate the field from a permanent magnet available here:

https://www.ti.com/lit/zip/slyr071

As an example, if using a 12mm cube of strong Neodymium (grade 52), the field at 300 mm is only about 14 uT.  However at a close range of 5 mm the field is about 216 mT.  If the sensor were placed some distance from the magnet where the output of the sensor is not saturated and opposite from where the vehicle is, it might be possible to detect changes, but this is entirely dependent on how much the vehicle interacts with the magnetic field.  As the vehicle approaches, the field would be drawn away from the sensor, and you should experience a shift in magnitude.  This would require more direct testing to verify how practical a solution this might be.  I would recommend acquiring a reasonable magnet for your application and the TMAG5170UEVM or TMAG5273EVM to evaluate the range for various sizes and ranges of ferrous material.

Thanks,

Scott

Madhav,

Our magnetic sensors are currently all Hall-effect based devices which typically do require some magnetic field source, but the earth's magnetic field is generally too weak. A typical value for what you might measure is 30 uT, which is just above the input referred noise of some of our more sensitive Hall-effect devices.  With TMAG5170 at the highest averaging setting, for example, I am able to see some change on the output when I swipe a steel object past the sensor at close range.  I do not know how much deflection to expect from an object like a car at a different range.  

Thanks,

Scott

Madhav,

Inductive sensing is able to detect the proximity of conductive materials, but range is limited similar to the Hall-effect sensors.  For longer range sensing as a backup to mmWave sensing, you could consider using Ultrasound.  This would work from either above or below and would be able to provide information when an object enters the target area.

https://www.ti.com/sensors/specialty-sensors/ultrasonic/overview.html?DCMP=ultrasonicsensing&HQS=sva-psp-isc-ultrasonicsensing-vanity-lp-ultrasonic-en

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/748143/faq-ultrasonic-sensors

Thanks,

Scott