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LMP7721: Electro-chemical sensor can not work with LMP7721

jianxin ma
Prodigy 10 points
Part Number: LMP7721

Tool/software:

Electro-chemical oxygen sensor output connect to LMP7721, the output of LMP7721 is not right. (output is very high)

Connect a current source to LMP7721, the output of LMP7721 is right.

The output of electro-chemical sensor and current source are same(about 1nA to 1000nA). 

The strange thing is, if I connect an old sensor(worked after a long time) which output is several nA, the output of LMP7721 is right.

I guess it is something about impedance.

  • 0
    TI__Guru 60566 points

    Hello Jianxin,

    Are you sure the sensor is not damaged? If two out of the three test cases are working, that seems to point to a bad, or stressed, sensor.

    Oxygen sensors can become damaged if the terminals are allowed to float. They can build up a voltage across the membrane with open pins, which causes damage.

    If they were shipped with a shorting pin, then the shorting pin should be placed across the sensor pins whenever the sensor is not being used.

    It can take minutes to days for a stressed sensor to recover.

    The circuit should also contain a shorting FET to make sure the input pins are shorted while the power is off.