| Summary: | 碩士 === 國立彰化師範大學 === 機電工程學系 === 101 === In the past, before the start of non-dispersive infrared (NDIR) measurement method, it required preheating light source to achieve infrared radiation of the stable output, and it often took about 2 to 15 minutes. In recent year, under the requirement of fast and high-resolution gas concentrations, the light source control and modulation techniques continue to improve. The use of correlated double sampling (CDS) and pulse width modulation (PWM) technology makes the measurement time significantly shorten to a few minutes.
We propose a novel and adaptive modulation technique, by using the thermal radiation sensor to detect gas concentration, to read the thermal radiation sensor signal to monitor the light source heating process, and to construct a calculus for feedback control infrared source of light and dark time empty proportion (Duty). In addition, it read CO2 sensor output signal to calculate the rise time under different gas concentration of the further verification. Furthermore, it applied the successive modulation pulse width of the feedback control as a research framework and it effectively and significantly reduced the time of boot preheated detection within seconds.
This innovative technology in the common air CO2 1500ppm can detect the concentration values within 20 seconds. Moreover, the signal-to-noise ratio (SNR) in atmospheric CO2 is able to maintain concentration between 1500 ~ 3000ppm that makes numerical values more than 30dB become more accurate and stable.
|
|---|
