Non-dispersive infra-red (NDIR) measurement of carbon dioxide at 4.2μm in a compact and optically efficient sensor

Abstract

Non-dispersive infra-red (NDIR) gas detection has enjoyed widespread uptake as a result of development of devices in the standard miniature format for gas sensors, consisting of a cylinder with external dimensions of 20 mm diameter x 16.5 mm height. We present a new design for such a sensor, making use of low-cost injection moulding technology. The design pays particular attention to the problem of maintaining a high optical throughput while providing an acceptable optical pathlength for gas detection. A detailed analysis of the design is presented, with the results of optical raytracing, showing a raytrace estimate for 4% of the total emitted radiation reaching each of two separated detector elements and a pathlength of 32 mm. Finally, we show experimental results obtained with as-manufactured devices, with a short-term limit of detection for carbon dioxide (CO 2 ) estimated at 1 ppm or a noise equivalent absorption (NEA) of 3 x 10 -5 AU. Highlights New design of non-dispersive infra-red (NDIR) sensor for CO 2 and other gases  Standard miniature format for gas sensors -a cylinder 20mm D x 16.5mm H  Raytrace -estimated 32mm pathlength  Manufactured in volume using gold-coated injection-moulded reflective optics  Short-term limit of detection 1ppm CO 2 , noise equivalent absorbance 3x10 -5 AU

Temperature Compensation Methods of Nondispersive Infrared CO2 Gas Sensor with Dual Ellipsoidal Optical Waveguide

“…The typical filter characteristics for CO 2 measurement using two IR detectors were described previously, (14) alongside the gas absorption spectrum, with the measurement whereby the chosen CO 2 and reference sensors do not overlap significantly with the absorption bands of other gas species present in the application.…”

A measurement strategy for non-dispersive ultra-violet detection of formaldehyde in indoor air: spectral analysis and interferent gases

“…Airborne particles were not considered in this project but may have to be considered or eliminated when using a detection system 'in situ', potentially by filtering. Many gas detectors, for example those based on non-dispersive infrared detection, are based on gas diffusion into the optical path through a particulate filter [29].…”

“…The method described here has a number of advantages over current systems that it shares with non-dispersive infrared gas detection (NDIR), including simplicity of manufacture, requirement of few, low cost components and a small size [29]. It follows similar principles to NDIR except that it operates in the ultra-violet region of the spectrum.…”

Capacitive CO2 Sensor

“…Although several applications for the monitoring of CO2 are possible, there are only few existing devices to detect CO2 in the desired environments, these devices using either optical or resistive methods. Optical detection based on non-dispersive infrared (NDIR) method is one well-known way to detect gases [5]. CO2 sensors based on the NDIR principle are accurate, allow fast measurements and have a good long-term stability.…”