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DRV411: Accurate Magnetic Field sensing up to 15mT

Martijn de Boer
Prodigy 30 points
Part Number: DRV411
Other Parts Discussed in Thread: DRV425, DRV401, DRV421, DRV5013, DRV5055-Q1

Hello,

I need a solution to measure a static magnetic field up to 15mT. The challenge is to find a solution with a very low drift on the gain sensitivity. We are aiming for < 0.3% full scale long term gain drift (> 3 years). A Fluxgate technology would probably fit, but the DRV425 can only measure up to 2 mT. Is there a application note or can you give me some guidelines in solving this with the DRV411 and an external fluxgate coil? It needs to be very compact. Temperature stability will be solved in software and offset drift is not crucial by the way for our application.

Thanks,

Martijn de Boer

  • 0
    TI__Genius 14825 points
    Martijn,
    Due to the holiday weekend, our experts will be delayed with their response until Monday.

    Have you looked into Hall sensors? They have a wider range but are less accurate.
  • 0 in reply to Jason Bridgmon
    TI__Mastermind 26475 points

    Martijn,

    The DRV411 drives an external hall sensor.  The DRV401 drives and external fluxgate coil.  Both these sensor then drive a compensation coil to drive the flux at the sensor to zero.  This is a feedback closed loop system where the DRV device needs to compensate the magnetic field to zero.  It needs this feedback to operate correctly.  Let me explain.

    So the way these two devices work is they measure a magnetic field through the sensor (hall or fluxgate) and drives a compensation coil in the opposite direction to compensate the flux to zero.  The magnetic field which can be from any source but normally through a magnetic core which concentrates the flux.  Our device either the DRV401 or DRV411 then drives a compensation coil wrapped around the magnetic core to drive the flux to zero through the core.  So the magnetic field is sensed by measuring the current required to drive the field to zero by driving the compensation coil. 

    Normally because the magnetic core has the same magnetic gain for the compensation coil and the primary current to be measured the magnetic gain variation plays a lower role and we get the Compensation Coil coil* Number of Turns = Primary Current.  If you are not measuring a current the device will still need to compensate the magnetic field and the magnetic gain plays a bigger role.  

    With typical magnetic core permeability having a large drift I am not sure if you can create a similar situation that your measuring a current where the magnetic gain or your magnetic field you are sensing and the compensation coil have the same magnetic gain.  Also the DRV401 and the DRV411 are both designed for current measurements.  

    Can you please provide details on how you were planing to compensate the sensor.  Also if you would like to experiment will less effort of getting an external flux gate you can attempt using the DRV421 which is similar to the DRV401 with an integrated fluxgate sensor.

  • 0 in reply to Javier Contreras4
    Prodigy 30 points

    Hi Javier,

    Thanks for you reply and explaining the scope of applications of these chips so well. I understand that by using this closed loop and driving the flux to zero the offset of the flux measurement plays a much bigger role and not the gain. Currently there are magnetic field sensors using fluxgate coils available with much higher gain accuracy than hall-effect sensors. They probably use an very well designed coil with special magnetic core material and there probably is no easy way of implementing this by using a combination of these coils + DRV401.

    Are there any statistics or expected tolerances about the Sensitivity Drift Over Lifetime of the hall-effect sensor of TI?

    Best regards,

    Martijn

  • 0 in reply to Martijn de Boer
    TI__Mastermind 26475 points
    Martijn,

    Please excuse my delay. I will contact one of my hall-effect experts and let you know.
  • 0 in reply to Martijn de Boer
    TI__Mastermind 20985 points

    Martijn, the DRV5013 has shown no measurable shift in accelerated lifetime testing.

    Best regards,
    RE

  • 0
    TI__Mastermind 20985 points
    Martijn, in response to your first post, please check out the DRV5055-Q1. The "A1" version has a ±21 mT range. Initial lifetime data shows Sensitivity drift to be <0.5%.

    Best regards,
    RE