A low cost, optically efficient carbon dioxide sensor based on nondispersive infra-red (NDIR) measurement at 4.2μm

Abstract

Non-dispersive infra-red (NDIR) gas detection has enjoyed a widespread uptake as a result of the development of sensors in the so-called pellistor format, 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 new 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 of 4% of the total emitted radiation reaching each of two separated detector elements and an optical pathlength of 32mm. The high throughput provides a number of advantages in helping to overcome detector noise in NDIR measurements. Finally, we show experimental results obtained with asmanufactured devices, demonstrating the superior signal to noise ratio achieved in measurement of carbon dioxide (CO₂). We believe the optical efficiency of the device, and the improved signal to noise ratio that results from this, to be a record for a device of these dimensions.