• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 1239 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Analog front end design for electrochemical gas sensors

user5175262
Prodigy 10 points
Other Parts Discussed in Thread: LMP91000, ADS1226, LMP90100, ADS1120, ADS1220, ADS114S06, ADS124S06

Hello,

I was working for some months with electrochemical gas sensors typically from Alpha Sense company which require an analog front end to be designed. Until now I did some prototyping and I have created some AFE using operational amplifiers and other passive components. Lately I ran on the LMP91000 chip from TI and seems very nice especially for 3 pin electrochemical gas sensors. Until now I used the A4 sensors from alphasense and I did not considered this chip also from the fact that those sensors have 4 pins and an external operational amplifier was required in addition to the LMP. 

In this moment I need to use sensors from spec-sensors.com which are 3 pin and LMP91000 can be used, but those sensors also have a smaller output current typically 4.5-20 nA/ppm. I need to be able to measure tens of ppbs therefore I suppose I need a big amplification. Moreover I need to have 4 of them on a single board. Alongside with the 4  LMP91000s I want to use a 24 bit ADC to convert the output of the AFE into numerical form. I have found the following ADC from TI: ADS1226 which has 2 differential channels therefore for 4 sensors I will need to use 2 of them and LMP90100 which has 4 differential channels and also another PGA inside which, I think, will help with the amplification.

Last note that I want to mention is that I am not an electrical/electronic engineer, but a computer science one and therefore I have limited knowledge of analog design. 

My questions are: is the LMP91000 suitable for those sensors(from spec)? Is the LMP90100 ADC the better choice to go along with LMP91000 AFE or should I seek another one? Any other guidance when using such sensors is welcome.

Thank you!

  • 0
    TI__Expert 5695 points
    Hello user5175262,
    As an starting point to determine if the LMP91000 is a good fit for your 3 pins sensors I recommend to use a design tool called Webench(r). This tool can be launched going to the webpage with link listed below and is located in the middle-right portion of the page. The Webench(r) interface for LMP91000 will allow you to select on different sensors or load the key parameters (e.g. sensitivity nA/ppm, full scale range ppm, etc.) of yours if is not there. There is a nice tutorial before using the tool.
    www.ti.com/.../toolssoftware

    The ADS1226 looks a great ADC option due to an excellent dynamic range and programmable gain. We found that for majority of applications the ADCs inside most common micro controllers (typically 12-16 bits) are good enough. Please refer to the applications section (page 24 on the LMP91000data sheet).
    www.ti.com/.../lmp91000.pdf

    Hope this helps and let us know if you need another question.

    Regards,
    Jose
  • 0 in reply to Jose Arteaga4
    TI__Mastermind 22205 points
    Hello user5175262,

    I just wanted to comment on the potential ADC options. The LMP91000 provides a single-ended output. In that case you need an ADC that can measure 4 single-ended inputs.
    I would look at ADS1220 (24 bit) or ADS1120 (16 bit) or if better performance is required then ADS124S06 (24 bit) and ADS114S06 (16 bit).

    Regards,