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LMP91002: Configure the H2S sensor using Sensor AFE Software.

abhay bellale
Prodigy 80 points
Part Number: LMP91002

Hi team 

We have using LMP91002 on project, we have referred same reference design which is recommended by TI and we are getting 500mv when no gas applied at sensor.

 

 can we assumed  500mV as 0 ppm /100 ppm /1000 ppm gas ?

 

We need one help how to convert mv to ppm ? P

Thanks

Abhay 

  • 0
    TI__Guru* 91146 points

    Dear Abhay - 

    1. Did you by chance use the LMP91xxx EVM and GUI, and one of the sensors listed in that database for your project? If not, please have a look. 

    Here, with this first H2S sensor choice as an example, you can see Vref is external, Vref divider is 20%, TIA gain is set with 35kOhms

    and here, if you are using the EVM and GUI with your sensor, you can convert mV to ppm in that tool (see above)

  • 0 in reply to Josh Wyatt
    Prodigy 10 points

    Thank you Josh for the reply.

    However, we want to know how this tool is converting mV to ppm for H2S-B4 sensor.  Does this use a formula or any look up atble etc?

    Because we need to implement that in to our system code.

    Thanks in advance

  • 0 in reply to balakrishna reddy1
    TI__Mastermind 38985 points

    Hi balakrishna,

    The H2S-B4 specifies a typical sensitivity of about 2025nA per ppm. If this current is passed through LMP91002's RTIA, it would develop (2025nA*RTIA) volts per ppm.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 80 points

    Hi Ren, 

    If i have same sensor H2S-B4 and it support upto 2ppm, as per your above formula 2025nA * RTIA is my calculations are correct  ?

    ppm Sensor Min-Sensitivity=nA/ppm  Max-Sensitivity=nA/ppm RTIA(ohm) min mV=Sensitivity * RTIA Max mV=Sensitivity * RTIA
    1 H2s-B4 1450 2150 2750 3.9875 5.9125
    1   1450 2150 3500 5.075 7.525
    1   1450 2150 7500 10.875 16.125
    1   1450 2150 14000 20.3 30.1
    ppm Sensor Min-Sensitivity=nA/ppm  Max-Sensitivity=nA/ppm RTIA(ohm) min mV=Sensitivity * RTIA Max mV=Sensitivity * RTIA
    2 H2s-B4 1450 2150 2750 7.975 11.825
    2   1450 2150 3500 10.15 15.05
    2   1450 2150 7500 21.75 32.25
    2   1450 2150 14000 40.6 60.2
    2   1450 2150 35000 101.5 150.5
  • 0 in reply to abhay bellale
    TI__Mastermind 38985 points

    Hi abhay,

    It looks reasonable to me.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 80 points

    Hi Ren, 

    Thanks for reply, I have some concern reading when connected H2B4 to EVK.

    I have not applied the gas even though I am getting 500mv as output and its not matching with table i shared last communication (you seen below as well). 

    surprisingly i am getting out of range output voltage if you see below tables for 2ppm is can get 100-150mv voltage for H2S-B4 sensor. 

    And H2S B4 is 4 lead sensor, we connecting onlt CE, WE and RE, we are ignoring Ax (pulling down to GND)

    For getting Voltage to ppm formula, if I need to sign NDA so I can do it. 

    Thanks,

    Abhay 

  • 0 in reply to abhay bellale
    TI__Mastermind 38985 points

    Hi Abhay,

    I don't have further information on the H2S-B4 device which is not sold by TI. There's no need for NDA. The H2S-B4 datasheet which is available on the web shows 1450-2600 nA/ppm, which is what I reported previously as a typical value.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 80 points

    Hi Ren, 

    Thanks for your reply. 

    Leave about h2S-b4 sensor. you take any sensor which you have tested on your EVL kit and share us result for our reference. 

    Also I observed Vout I am getting 500mV, without any senor connected to your EVK  is this correct? 

    Thanks

    Abhay

  • 0 in reply to abhay bellale
    TI__Mastermind 38985 points

    Hi Abhay,

    How are you configuring the LMP9 device? There are several settings which change behavior. With no input, it could float at that level. By default, the amplifier is not on. 

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 80 points

    Hi Ren, 

    Is it possible to have one quick online support tomorrow, please suggest your suitable time, so I can setup team meeting 

    Thanks

    Abhay 

  • 0 in reply to abhay bellale
    TI__Guru* 91146 points

    Abhay - 

    Hopefully we can resolve this, here in this forum.

    I would go ahead and connect your sensor, and here in this case, you might want to consider choosing (to start with) the settings shown in the GUI for the CityTech 7HH sensor as it is closest from the choices, to the sensor you are using.