Compiler/LMP91000: Issue to connect gas sensor AFE with LMP7721

Nikunj Panchani

Intellectual 560 points

Part Number: LMP91000
Other Parts Discussed in Thread: LMP7721, LM4040, HDC2010, HDC2080, REF3020, REF3120

Tool/software: TI C/C++ Compiler

Hello Community,

I configured my hardware using LMP91000 and LMP7721 as shown in thread,

Also, I used equation to find gas sensor concentration using,

But, after reading data from analog pins I can't get output as expected both WE and AE pin gives nearly same output sometimes it shows negative ppm.

Could anyone tell me that which config I did wrong?

Thanks in advance,

Nikunj

over 4 years ago

0 Josh Wyatt over 4 years ago

TI__Guru* 91086 points

Nikunj -

Are you using EVMs or your own boards?

Can you show your schematic? (as you refer to a schematic and a concept of a schematic in those posts) - its probably best to see what you wired up to start out with.

BR -

Josh

0 Nikunj Panchani over 4 years ago in reply to Josh Wyatt

Intellectual 560 points

Hello Josh Wyatt,

I attched my baord's schematic4 lead_Sensor_LM7721_Breakout_Board.pdf

Regards,

Nikunj

0 Josh Wyatt over 4 years ago in reply to Nikunj Panchani

TI__Guru* 91086 points

Nikunj -

thanks for the drawing - will study this and get back to you by early next week.

0 Josh Wyatt over 4 years ago in reply to Josh Wyatt

TI__Guru* 91086 points

Nikunj -

I am not sure where you are getting your H2S sensor from, but i did find one at spec sensors - if you register and login https://www.spec-sensors.com/register/ to see the schematic for the their EVM, they show with their sensor and the LMP91000 having the two working electrodes tied together. You may want to use their sensor and this design. They have entire thing online.

Also, please note this reference uses other parts that TI has good crosses for as well - to include the HDC2080 or HDC2010 for temp and humidity, MSP430 for MCU, TLV8541DBVR for the op-amp, and LM4040/LM4050 or REF3020 / REF3120 for the 2.048V voltage reference.

0 Nikunj Panchani over 4 years ago in reply to Josh Wyatt

Intellectual 560 points

Hello Josh,

Thanks for your reply,

The sensor I have is alphasense H2S-A4. I use LMP91000 for working electrode and LMP7721 for auxilary electrode. only LMP91000 gives output(uncorrected ppm) in mV, LMP7721 gives always 0mV in output. But according to equation given in link that I posted above auxilary output do matter to get final ppm(corrected).

Can you suggest how can I get auxilary electrodes output.

Regards,

Nikunj

0 Josh Wyatt over 4 years ago in reply to Nikunj Panchani

TI__Guru* 91086 points

Nikunj -

Did you look at the Spec Sensors reference?

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Compiler/LMP91000: Issue to connect gas sensor AFE with LMP7721