LMP91000: Oxygen measurement with the LMP 91000

Esteban Lasa

Part Number: LMP91000

Hello everyone,

We designed a circuit using the LMP91000 for measuring oxygen with the S+40XLF sensor. This sensor needs a bias voltage of -600mV.

Im using the Arduino IDE for testing the circuit and the results are not being the expected ones. With a 21% of oxygen concentration in the air, the output singal of the sensor must be of 100 microAmps. However, my output signal is of 235 microAmps since the value of the signal in the C2 pin is 0.001875V, (3.3-0.001875)/14000=0.000235 A

The output singal in C2 and the temperature signal in Vout are connected with a ADS115.

The configuration of the LMP is the next one:

Rload = 100 R

Rtia = 14K R

Vbias = 18% of the external reference (3.3V) = 600mV

Bias sing = negative (-600mV)

Mode = 5 (3 lead)

Internal zero = bypass (3.3V in the non inverting pin of the TIA)

I woudl appreciate if you could send me some help with this issue.

over 5 years ago

0 Gordon Varney over 5 years ago

TI__Genius 9380 points

Lasa,

I am not familiar with your sensor, however most 40x oxygen sensors are for a 2 wire configuration. You are in 3 wire mode.

Please check with the manufacture of your sensor to make sure you have it in the correct mode. Let me know if this doesn't fix your issue.

0 Esteban Lasa over 5 years ago in reply to Gordon Varney

Prodigy 200 points

Thanks for your reply Gordon.

Unfortunately, I think thats not the real problem since in the reccomended circuitry for my sensor a 3 lead configuration is used.

I attach the schematic provided by DD Scientific, the supplier of our oxgen sensor.

PastedGraphic-4.pdf

0 Esteban Lasa over 5 years ago in reply to Esteban Lasa

Prodigy 200 points

Sorry, this is the right one.PastedGraphic-5.tiff

0 Josh Wyatt over 5 years ago in reply to Esteban Lasa

TI__Guru* 91206 points

you may want to use the settings from the EVM in this case, with the LMP91000, you would use the 3 terminal sensor in 2 terminal mode, as the individual circuit components you see in the reference that came from the manufacturer, are more or less built into the LMP91000.

you would also possibly set Vbias offset to 0% and or choose a sensor from what is known to work - see the EVM GUI, screen shots below

this is with 4OX-2 sensor, probably very similar to the one you are using.

Sensors

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LMP91000: Oxygen measurement with the LMP 91000