Abstract
This paper describes development of a novel mid-infrared light emitting diode (LED) and photodiode (PD) light source/detector combination and use within a non-dispersive infrared (NDIR) carbon dioxide gas sensor. The LED/PD based NDIR sensor provides fast stabilisation time (time required to turn on the sensor from cold, warm up, take and report a measurement, and power down again ≈1 second), longevity (>15 years), low power consumption and low cost. Described performance is compatible with “fit and forget” wireless deployed sensors in applications such as indoor air quality monitoring/control & energy conservation in buildings, transport systems, horticultural greenhouses and portable deployment for safety, industrial and medical applications. Fast stabilisation time, low intrinsic power consumption and cycled operation offer typical energy consumption per measurement of mJ's, providing extended operation using battery and/or energy harvesting strategies (measurement interval of ≈ 2 minutes provides >10 years operation from one AA battery). Specific performance data is provided in relation to measurement accuracy and noise, temperature performance, cross sensitivity, measurement range (two pathlength variants are described covering ambient through to 100% gas concentration), comparison with NDIR utilizing thermal source/pyroelectric light source/detector combination and compatibility with energy harvesting. Semiconductor based LED/PD processing together with injection moulded reflective optics and simple assembly provide a route to low cost high volume manufacturing.
Highlights
There is a growing need [1] for low power consumption, fast stabilizing wireless compatible carbon dioxide (CO2) gas sensors, driven by current and incoming legislation requirements [2,3] for CO2 gas monitoring/control within building and transport environments
Use of CO2 concentration monitoring/control provides a means of providing indoor air quality (IAQ) which can be set to suit level of people occupancy through demand control ventilation (DCV) [6,7]—human exhaled air is rich in carbon dioxide gas, waste product of cellular respiration, and CO2 gas concentration monitoring provides an accurate means of determining people occupancy in a known volume
This paper describes an all solid state, low power consumption, reliable and low cost non-dispersive infrared (NDIR) CO2 gas sensor, incorporating light emitting diode (LED) light sources and photodiode (PD) detectors [20,21], combined with state of the art signal processing matched to use of LED/PD’s
Summary
There is a growing need [1] for low power consumption, fast stabilizing (minimal time required to turn on the sensor from cold, warm up, take and report a measurement, and power down) wireless compatible carbon dioxide (CO2) gas sensors, driven by current and incoming legislation requirements [2,3] for CO2 gas monitoring/control within building and transport environments. Such autonomous CO2 sensors, powered from extended battery life/energy harvesting sources, provide a lower cost route to flexible deployment compared with hard wiring of CO2 sensors into building or transport systems infrastructures. LED/PD offer the advantage of low power consumption, high source emittance, fast modulation rates, room temperature operation, fast stabilisation time and brings with it the cost benefits of semiconductor manufacturing techniques [22]
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