• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 250 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LMP91000: LMP91000SD application issue

Cherry Zhou
Mastermind 22235 points
Part Number: LMP91000

Hi team,

Project: Carbon dioxide gas detector project, using LMP91000SD, which currently has the following problems:

1) When gas concentration is 0 to 30PPM, the ad value range is only 0x2500. How to increase it?

2) When adding 30PPM concentration gas, the rise is slow and takes a few hours to stabilize. And when removing the gas, the decrease is slower. How to fix it? 

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Genius 9380 points

    Cherry,

      It would help if I knew the part number of the sensor you are working with. What I can tell you is that the LMP91000 uses a transimpedance amplifier (TIA). The RLoad is really a shunt. The TIA measures the voltage across the RLoad to measure the current in the sensor. If RLoad is 100 Ohms you will have the largest voltage drop making it the most sensitive. Lowering the RLoad value will lower sensitivity but provide more head room for higher level measurements. The gain is also important as it will scale the measurement as well. Try lowering the VREF to 20% to get more headroom. Lowering the RLoad value and adjust the gain as needed to get as close to the max level you want to measure.

    The time to settle does not sound right. It sounds like your bias is not correct. My suggestion is to download the software for this part. You don't have the EVM but don't worry about that. Open the software and ignore that it doesn't have a board attached. Look for a sensor close to the sensor type and part number that you have. It may not be exact but that is ok because all you want is the setup information as a starting point. Adjust the settings as needed.