One of my customer is in initial testing phase of the NDIR gas bench with Thermopile sensor ST120Quad with your LMP91051
Analog front end IC in the output of Thermopile sensor for signal conditioning.
They observed that the amplitude of sensor (at the output of AFE) is less. Please find attached the signals captured during passing
Fresh air and when passing a Gas mixture( CO= 3.57%, CO2=14.50% and Propane = 2090ppm). Channel 1 is CO and HC, Channel 2 is CO2 and Ref.
Gain set in channel 1 is = 4000 and Channel 2 = 8000 .
The channel switching time set is 5ms. IR LED ON/OFF time is 250ms( 250 ms ON and 250ms OFF).
Please let us know whether this is ok? waveforms are attached for reference. please advise.
I will double check the costumer waveforms and the device settings with our LMP91051 designer, and I will let you know our comments as soon as possible.
In reply to Carmine Iascone:
Thanks for your reply. please find attached schematics, please help to review the same and advise your valuable feedback, thanks.
Rgds/Aravind.SCHEMATIC1 _ Signal conditioner.pdf
In reply to Aravind .R:
The typical NDIR Sensing Application Circuit using the LMP91051 is shown below:
So basically, for each gas that the customer want to detect, it is necessary to use a single LMP91051, and connect the IN1 pin to the Active thermopile, and the IN2 to the reference.
Reviewing the customer schematic, the configuration of U3 is not correct, because the IN2 pin should be connect to the REF thermopile (pin 3, of the ST120 thermopile), and for the HC detection it is necessary to use a further LMP91051.
Please let me know if you have any comments.
Thanks. please review the attached schematics and also help to reply for below query.
Rgds/Aravind.7026.SCHEMATIC1 _ Signal conditioner.pdf
Look forward for valuable reply on previous post, thanks.
We reviewed the schematic, and our comments are the following:
Switching from LMP91051 to LMP91050, there are the following advantages/disadvantages:
LMP91051 provides the flexibility to separate the analog and IO voltage references, if needed, in order to avoid the use of additional level shifters. Unfortunately, this configuration is not available in the LMP91050.
Please let me know if this reply to your questions or you needs further information.
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