Summary: | 碩士 === 國立彰化師範大學 === 機電工程學系 === 100 === For the detection of CO2 gas concentration, non-dispersive infrared (NDIR)
play the major role of gas sensing technique in science and technology. The
working principle of NDIR is based on the spectral absorbance on some specific
wavelengths corresponding to the detection gas and the reduction of absorption
is monotonic proportional to the gas concentration. Usually, NDIR technique
includes a broad band infrared light source and an infrared sensor with a
specific bandpass filter in front. Most of all, the response time of NDIR
measurement will be dominated by the warm-up time of the light source which
will achieve a stable spectral radiation for a long time up to 10~30 minutes.
Therefore, this long warm-up time will limit the applications of gas
concentration measurement and even worse, some mistakes will happen if the
measurement operation does not fit the requirement of enough time to wait the
thermal radiation stability.
We propose a novel fast warm-up time technique with an over-drive
procedure which pumps up more power to the light source in the beginning and
then comes back the normal operation condition with high SNR detection. This
research is realized also with the Correlated Double Sampling (CDS) circuit and
different modulation experiments are analyzed to find the optimal operation
conditions. The research focuses on the CO2 concentration measurement and we
choose the Heimann Sensor J22 CO2 with a 4.2μm filter. The CDS operation is
performed with two phases: the first phase is to turn on the light source with full
power and the second phase with lower power or even turn off.
Reduce the warm-up time from the conventional design with 865s to the
best result of 30s. It shows almost 30 times less than before. Under the same lighting power, for different period of two phase, the best results reduces the
warm-up time to 103s. Combining these two results, we propose an optimal
solution to improve the measuring efficiency and a possibility of performance
enhancement.
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