Hello!
At the moment I am working on NDIR sensor using LMP91051 chip. I am trying to make a hydrocarbon oxygen detector. I use HIS E222 F3.91-90 F3.375-190 G4300 as a thermopile sensor. The radiation source is an IR lamp 1089. I give the switching circuit below:
I ran into a problem of the following nature. With open contacts J1 and J2 at the output of the LMP91051 chip, the signal has the form:
The output signal does not change when gas is supplied (C3H8-nitrogen with a volume fraction of component 1.394%):
When the contact J2 is closed, the output signal has the form:
The same signal, but on a different scale without gas supply:
And with the supply of C3H8-nitrogen with a volume fraction of the component of 1.394%:
You can see that the signal amplitude decreased from 650 mV to 600 mV (change in the amplitude of the output signal by 7.7%). The output voltage decreased from 2.53 to 2.47 V (2.4% change).
The output voltage and the amplitude of the output signal with the closed contact J1 does not change when the gas is supplied and has the form:
I use the following LMP91051 configuration:
- Frequency of a pulsation of a lamp - 2 Hz;
- Channel switching frequency - 100 Hz;
- System offset: - 700 mV;
- Lamp supply voltage 5 V,
- The supply voltage of the chip is 3.3 V.
- External filter enabled.
- System gain is 8000 V/V.
- Device Configuration register, value: 0b01110110 and 0b11110110 (the value switched by a microcontroller with a frequency of 100 Hz)
- DAC Configuration Register, value: 0x6В
Questions I would like to ask you:
1. What may be the reason for the difference between the output signal of the LMP91051 chip from the one given in the description, as well as the lack of response of the output signal to the gas supply of C3H8-nitrogen with a volume fraction of the component of 1.394%?
2. Is it possible to organize channel switching without using a microcontroller?
Best wishes
Rybakov I.V.
