Measuring magnetic field (-10000 to +5000 Gauss) using AD22151

I made a magnetic field module using the AD22151 sensor based on the bipolar configuration in the datasheet. The sensitivity S is determined by R3 and R2. Theoretically speaking, my sensor module should be able to measure -8000 to +8000 Gauss.

However, when I measured the magnetic field over a hard magnet, the output voltage easily got to 4.69 V which is the maximum output of the sensor. I measured the same magnet using a Gaussmeter, the reading is 3300 Gauss. Do I misunderstand the gain equation given by the datasheet?

Someone asked questions about AD22151 in the forum. The answer said the sensor could only measure -2500 to +2500 Gauss in bipolar configuration and 0 to +5000 Gauss in the unipolar configuration. If this is true, then it may answer my question. But the thing is that the datasheet shows that the magnetic flux density that can be measured is Unlimited which is different from what was answered in the forum.

If the sensor has a limitation on the measured flux density, is there any other magnetic field sensor that has a larger range of measurement?

AD22151.pdf
  • 0
    •  Analog Employees 
    on Jul 26, 2017 11:52 PM

    Hi,

    The gain equation is given in the data sheet as follows:


    Since you are in bipolar configuration, by measuring 3300 Gauss, the output was railed to Vcc.

    Unfortunately, as what you have read,  AD22151's minimum stable gain is 2 meaning the sensor could only measure -2500 to +2500 Gauss in bipolar configuration and 0 to 5000 Gauss in the unipolar configuration.

    I'll contact the product owner for the clarification in Abs. Max rating in the data sheet.

    You can review our Magnetic Field Sensors to see if any of these would suit your needs.

    Regards,
    Goz

  • 0
    •  Analog Employees 
    on Jul 27, 2017 7:08 PM

    Hello,

    The unlimited rating in the abs. max indicates that whatever the magnetic flux density value you subject the device, it will be still be functional but may not operate within the given specifications.

    Unfortunately, the device's limitation is it can only measure reliably at 5000 gauss range. Subjecting the device in absolute maximum rating conditions over time may affect its reliability. 

    Regards,
    Goz

  • Hi Gauzz,

    Thank you for replying and contacting the product owner. The word "unlimited" in the datasheet is misleading to me. I really hope that different combinations of R3&R2 could generate designated gains in a wider range.

    I appreciate that you can let me know when the product owner gives you any feedback.

    Regards,

    ,Peng

  • Hi Goz,

    Thank you! That is a good news to me. At least the sensor can work in a larger range of magnetic field.

    But as you saw in my schematic diagram and the gain equation, the new sensitivity is 0.2932 mV/G. The actual flux density measured by a Gaussmeter above the magnet surface is 3300 Gauss. That means the output voltage is supposed to be 3300*0.2932*0.001+2.5 = 0.96756V+2.5V = 3.46756V. However, the output quickly reaches 4.69 V even though the magnet has not touched the magnet surface. Do you have any suggestion for modifying the sensitivity (gain) of the sensor?

    Best Regards,

    Peng

  • Hi Goz,

    I checked the datasheet again. It says:

    If I want a sensitivity of 0.2 mV/G, then the gain required would be 0.2/0.4 (mV/G)=0.5.

    so we have:

    Gain-1=R3/R2*0.4mV/G=-0.5<0

    Does that mean the new gain should be always larger than 1, thus the new sensitivity should be always larger than 0.4 mV/G? 

    If this is true, then the maximum flux density is actually still limited.

    Could you confirm my conclusion, please? Or could you let me know the contact information of the product owner?

    Best Regards, 

    Peng Peng