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Sensor AFE reading from O2-A2 & CO-AF

Natesan Palanivel72800
Prodigy 210 points

Other Parts Discussed in Thread: LMP91000EVM

Hello,

I have LMP91000EVM with CO-AF and connected via SPIO4 board. The readings at sensor AFE does not changes when I take close the diesel car exhaust(idle to acceleration). How to distinguish the presence of CO from a car in sensor AFE readings?. Similarly, how to distinguish the Oxygen levels from the sensor AFE readings?.

Best Regards

N Pal  

  • 0
    TI__Genius 16890 points
    Hello,

    The exhaust gasses of diesel are CO2 - 12%, H2O - 12%, O2 - 17%, N2 - about 59%. HC, CO, NOx, and PM are also present but in very low concentration, some tenths of one percent. (See www.dieselnet.com/.../emi_intro.php). Is the sensor able to detect such a low level of CO?

    Mike
  • 0 in reply to Michael Stout
    Prodigy 210 points
    Hello,
    Thank you for your reply. My query is towards Sensor AFE GUI.
    I hope the sensors are capable. CO-AF : Sensitivity: nA/ppm in 400ppm CO 55 to 90uA.
    Best Regards
    N Palanivel
  • 0 in reply to Natesan Palanivel72800
    TI__Genius 16890 points
    Hello,

    The CO sensor you selected is in the database that is in the GUI. You should be able to select it in the software and try it out. I am not sure what the CO ppm is the exhaust.

    Mike
  • 0
    TI__Guru 69646 points

    Hello Natesan,

    Make sure you click "Write to board" after first opening or making ANY changes (the little PCI board with arrow icon in menu bar).

    Also make sure, in the upper right corner, that the Vref_EXT is set to 2.5V and SUPPLY is 3.3V. These do not auto-update with the database selections.

    Make sure the board is working - Measure the VOUT test point on the board - it should match the "Output Voltage" graph in the GUI ("Output Format" pull-down => Output Voltage mV)

    it should read around 500mV. If it is reading too high (like 800mV) or too low, then the VREF entry above is incorrect (the VREF reference on the board is 2.5V).

    Remove the sensor and short CE to RE and measure CE to ground. It should be +500mV (20% of 2.5V). You should also see +500mV on the WE terminal - but this reading may be influenced by the DMM loading.

    With the sensor removed, you should read zero current or ppm. When you plug the sensor back in, you should see it "rail" for a few seconds then float back down to around zero.

    With the sensor removed, stick a 100K resistor between WE and GND2. You should read a current of +5000nA.

    A simple test of the sensor is the "shot glass" test.

    Get a small glass - a "shot glass" or small juice cup (not plastic or paper!) that fits over the sensor.

    Hold the glass upside down (mouth down) above the sensor and light a match under the glass so that the gasses and smoke rise into the glass.

    Then slowly and smoothly, without tipping the glass, lower the glass over the sensor.

    You should immediately see the concentration rise.

    BTW: Do not use a lighter, as the butane gas can cause erroneous readings and possibly contaminate the sensor.

    Be careful exposing the senor directly to exhaust gas - there are many other gases in the exhaust that can "blind" (cross-sensitivity) or even damage the sensor. Heat can also damage the sensor. Real exhaust monitors have filters before the CO sensor. It may take hours or days for the sensor to recover (assuming it was not damaged). Let the board run overnight so the sensor can recondition itself.

    Regards,

  • 0
    TI__Guru 69646 points
    Oh,... Also make sure that the "2-WIRE" jumper is REMOVED for the CO-AF sensor, and JUMPERED for the O2-A2 sensor.

    The O2-A2 is a "2 pin" sensor (no RE - should be a plastic RE pin), and the CO-AF is a "3-pin" sensor.

    Having the jumper in place will not damage the CO-AF sensor, but it just will not work.

    Regards,