Mipex MIPEX-04, User Manual, Page: 5 / 41

Optosense LLC USER MANUAL
Design department MIPEX-04 ULTRA-LOW POWER INFRARED GAS SENSOR
ESAT.100000.00.02 UM Revision 02 December 12th, 2016 Page 5 of 41
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2. DESCRIPTION
Sensor has several modifications for specific needs. They differ by photodiode and LED
types, calibration gases, measuring ranges etc. (see Appendix A).
Sensor is a smart integrated system and includes mirror optical system, photodiode and
LED, signal amplifiers, microcontroller, current driver of the infrared LED, UART interface signal
generator and forming voltage supply unit. Sensor microcontroller performs storage of unique
sensor calibration constants, processing of measurement results and concentration of measured
gas, and information exchange.
Sensor operating principle is based on NDIR technology, i.e. on selective infrared radiation
absorption by gas molecules.
Infrared radiation from LED permeates through a measuring diffusion-type gas cell and
arrives on signal and reference photodetectors, one of which detects radiation only in the
wavelength range of infrared radiation absorbed by gases, while the other one detects radiation
only in the wavel
ength range of 3.5…3.7 μm. Gas flowing through the cell absorbs the radiation of
the operating wavelength (
λ
s
) and does not affect the radiation of the reference wavelength (
λ
ref
).
Amplitude
U
s
of the photodetector operating signal varies with the concentration of the target gas in
accordance with the following equation:
U
s
U
ref
= exp(−[K(λ
s
) − K(λ
ref
)] ⋅ C ⋅ L)
where:
К(λ) – absorption coefficient at the predetermined wavelength;
L
– optical length of the cell;
С
– measured concentration of gas;
U
s
, U
ref
– signal amplitude at photodetector.
Differential dual wavelength method allows eliminating of water vapor, optical elements
contamination and other non-selective hindrances influence.
Target gases available for MIPEX-04 are listed in Table 1.
Table 1. Target gases for MIPEX-04 sensors
Target gas
Analytical tasks
description
Optical elements
code (see
Appendix A)
Spectral
characteristic
maximum
Notes
CH
4
Analyzing a gas mixture
containing methane as
the main component.
1
3.31

m
For the optical
elements sensitivity to
other hydrocarbons
see Fig. 4.
C
3
H
8
Analyzing a gas mixture
containing heavy
hydrocarbons. The
presence of methane is
negligible.
2
3.40

m
For the optical
elements sensitivity to
other hydrocarbons
see Fig. 5.