• Journal of Sensor Science and Technology
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• v.10 no.5
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• pp.279-285
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• 2001

The capnograph system for determining the partial pressure of carbon dioxide in the blood of a patient was developed based on the NDIR(non-dispersive infrared) absorption technology. NDIR gas analyzing method requires an optical absorption chamber and signal processing hardware. In this paper, we have designed and implemented NDIR type $CO_2$ gas chamber in consideration of the time response characteristics and lamp chopping frequency. And we have implemented signal processing hardware using two infrared sources to reduce the thermal background effect. The implemented gas chamber and signal processing hardware were tested in the temperature variation experiment and human expiratory experiment. The results showed that the system could produce a stable output signal and a good $CO_2$ gas concentration curve like a typical capnogram.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.81-82
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• 2005

본 논문에서는 두 개의 오목 반사경으로 형성된 광 공동 구조의 비문산 적외선 (NDIR) 가스센서를 제작하였다. 증폭비는 18,000 배, 램프 off 시간은 3초로 일정하게 하고 펄스 modulation 시간을 200ms에서 600ms까지 변화시켰을 때. 300ms에서 가장 효율적인 출력신호를 확보할 수 있었다. 그리고 $5^{\circ}C$에서 $45^{\circ}C$까지 $10^{\circ}C$ 간격으로 온도를 변화시키면서 이산화탄소의 농도를 0ppm에서 2000ppm까지 증가시켰다. 이때, 약 400mV의 전압변화가 있었다. 온도가 상승함에 따라 0ppm에서의 출력전압은 감소하는 양상을 나타내었다. 또한 온도변화 대비 출력특성과의 상관성 해석을 통하여 온도 보상 방법을 고안하였으며, 본 연구에서 제작한 센서모듈의 응답시간은 약 30초였다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.2
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• pp.36-40
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• 2009

In this paper we discuss about the practical implementation of a combined CO and CO2 dual sensor module that is adapted by NDIR (Non-Dispersive Infrared) method that measures the absorbance of gas like CO and CO2 by using gas particles' characteristics that absorb specific wave lengths of infrared ray. NDIR has a long life time, excellent measurement and precision compared to the existing contact types or chemical types of CO2 sensors. Since optical cavity technology that had been developed until now can measure CO2 only we research and develop an optimal optical cavity design and density-temperature calibration technologies that can measure CO and CO2 at the same time and is important to decide the performance of the sensor module according to well-designed wave guides of the different length.

• Journal of Sensor Science and Technology
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• v.25 no.2
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• pp.124-130
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• 2016

NDIR $CO_2$ gas sensor was built with ASIC implemented thermopile sensor which included temperature sensor and unique elliptical waveguide structures in this paper. The temperature dependency of dual infrared sensor module ($CO_2$ and reference IR sensors) has been characterized and its output voltage characteristics according to the temperature and gas concentration were proposed for the first time. NDIR $CO_2$ gas and reference IR sensors showed linear output voltages according to the variation of ambient temperatures from 243 K to 333 K and their slopes were 14.2 mV/K and 8.8 mV/K, respectively. The output voltages of temperature sensor also presented a linear dependency according to the ambient temperature and could be described with V(T)=-3.191+0.0148T(V). The output voltage ratio between $CO_2$ and reference IR sensors revealed irrelevant to the changes of ambient temperatures and gave a constant value around 1.6255 with standard deviation 0.008 at 0 ppm. The output voltage of $CO_2$ gas sensor at zero ppm $CO_2$ gas consisted of two components; one is caused by the HPB (half pass-band) of IR filter and the other is attributed to the part of $CO_2$ absorption wavelength. The characteristics of output voltages of $CO_2$ gas sensor could be accurately modeled with three parameters which are dependent upon the ambient temperatures and represented small average error less than 1.5% with 5% standard deviation.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1470-1471
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• 2008

We present a front-side micromachined thermopile with high sensitivity in the 3-5${\mu}m$ window, and discuss its application to a novel non-dispersive infrared (NDIR) $CO_2$ gas sensor with a light source emitting collimated light. The micromachined thermopile shows a measured sensitivity of 30 mV/W and a $D^*$ of $0.3{\times}10^8cm^{\surd}Hz/W$. Using this newly fabricated thermopile, we also have successfully developed a small, sensitive NDIR $CO_2$ detector module for accurate air quality monitoring systems in energy-saving building and automotive applications. The novel sample cavity comprising specular reflectors around the light bulb is configured to uniformly emit collimated light into the entrance aperture of the cavity in order to enhance the sensitivity of NDIR $CO_2$ detector.

• Journal of the Korean Institute of Gas
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• v.15 no.4
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• pp.51-55
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• 2011

This paper describes the temperature compensation algorithm using thermopile detector for nondispersive infrared methane gas sensor. From the output voltage of thermistor that is attached onto the infrared detector, the ambient temperature was extracted. The effects of temperatures on the properties of sensor module (the characteristics of narrow bandpass filter, optical cavity and infrared lamp, and gas absorption coefficient times optical path length) have been introduced in order to implement the temperature compensation algorithm. Even though the measurement error of developed sensor module was in the range of $\pm$ 1,500 ppm, after programming the temperature compensation algorithm, the developed sensor module shows a high accuracy less than +180 ppm error within $20^{\circ}C$ temperature variation.

• Journal of Sensor Science and Technology
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• v.25 no.5
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• pp.377-381
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• 2016

NDIR $CO_2$ gas sensor was prototyped with ASIC implemented thermopile sensor which included temperature sensor and White-Cell structure in this paper. The temperature dependency of dual infrared sensors ($CO_2$ and reference IR sensors) has been characterized and their output voltage ratios according to the temperature and gas concentration were presented in this paper for achieving temperature compensation algorithm. The initial output voltages of NDIR $CO_2$ gas and reference IR sensors showed $3^{rd}$ order polynomial and linear output voltages according to the variation of ambient temperatures from 253 K to 333 K, respectively. The output voltages of temperature sensor presented a linear dependency according to the ambient temperature and could be described with V(T) = -3.0069+0.0145T(V). The characteristics of output voltage ratios could be modeled with five parameters which are dependent upon the ambient temperatures and gas concentration. The estimated $CO_2$ concentrations showed relatively high error below 300 ppm (maximum 572 % at 7 ppm $CO_2$ concentration), however, as the concentration increased from 500 ppm to 2,000 ppm, the overall estimated errors of $CO_2$ concentrations were less than ${\pm}10%$ in this research.

• Journal of Sensor Science and Technology
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• v.26 no.3
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• pp.179-185
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• 2017

This article describes the characteristics of nondispersive infrared carbon dioxide gas sensor according to the temperatures and humidifies. In this researches, a thermopile sensor that included application-specific integrated circuit (ASIC) was used and the White-cell structure was implemented as an optical waveguide. The developed sensor modules were installed in gas chamber and then the temperature of gas chamber has been increased from 283 K to 313 K with 10K temperature step. In order to analyze the effects of humidity levels, the relative humidity levels were changed from 30 to 80%R.H. with small humidifier. Then, the characteristics of sensor modules were acquired with the increment of carbon dioxide concentrations from 0 to 2,000 ppm. When the initial voltages of sensors were compared before and after humidifying the chamber at constant temperature, the decrements of the output voltages of sensors are like these: 9mV (reference infrared sensor), 41 mV (carbon dioxide sensor), 2 mV (temperature sensor). With the increment of ambient temperature, the averaged output voltage of carbon dioxide sensor was increased 19 mV, however, when the humidity level was increased, it was decreased 14mV. Based upon the experimental results, the humidity effect could be alleviated by the increment of temperature, so the effects of humidity and temperature could be only compensated by the ambient temperature itself. The estimated carbon dioxide concentrations showed 10% large errors below 200 ppm, however, the errors of the estimations of carbon dioxide concentrations were less than ${\pm}5%$ from 400 to 2,000 ppm.

• Journal of Sensor Science and Technology
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• v.26 no.3
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• pp.168-172
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• 2017

A nondispersive infrared (NDIR) ethanol gas sensor was prototyped with ASIC implemented thermopile sensor, which included a temperature sensor and two ellipsoidal waveguide structures. The temperature dependency of the two ethanol sensors (with partially blocked and intact structures) has been characterized. The two ethanol gas sensors showed linear output voltages initially when varying the ambient temperature from 253 K to 333 K. The slope of the temperature sensor presented a constant value of 15 mV/K. After temperature compensation, the ethanol gas sensor estimated ethanol concentrations with larger errors of 20 to 25% below 200 ppm. However, the estimation errors were reduced to between -10 and +1 % from 253 K to 333 K above 200 ppm ethanol gas concentration in this research.

• Journal of the Semiconductor & Display Technology
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• v.12 no.3
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• pp.35-39
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• 2013

In this paper, we developed an optical sheet for LED lighting with integrated $CO_2$ gas and temperature sensor which can monitor at the indoor environment. The optical sheet for LED lighting is fabricated through PMMA(Polymethyl methacrylate) injection process using mold. This research enables to fabricate the reflective sheet, light-guide plate and the prism sheet in a optical sheet. The fabricated sheet demonstrates higher intensity of optical efficiency compared with single-sided sheets. The $CO_2$ sensor was fabricated using NDIR(NON-Dispersive Infrared) method and it has $0.0235mV/V{\cdot}PPM$ sensitivity. The temperature sensor was fabricated using RTD(Resistance temperature detector) method and it has $0.563{\Omega}/^{\circ}C $sensitivity.