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Electronics and Photonics



Fundamentals of Design and Engineering Electronics Hardware and Software



Fundamentals of Troubleshooting Electronics & Photonics



Lock-in and Signal Averaging Circuits for an NDIR Gas Spectroscopy Based Carbon Monoxide Detector (231 KB – PDF)



This application note describes two circuits (lock-in and signal averaging) for detection and measurement of low levels of Carbon Monoxide (CO), using Non-Dispersive Infrared (NDIR) gas spectroscopy. NDIR gas detection and measurement offers reliability, sensitivity, and immunity from false alarms for such applications as CO detectors. The lock-in circuit is analog in nature and enables the measurement of CO levels down to 1 ppm, and meets CSA requirements for residential CO detectors; while the signal averaging circuit uses a mixed-signals approach (analog and digital), inherently capable of much higher resolution than that of the analog circuit.


The fundamental approach of signal averaging described in this application note is suitable for the detection of other types of gas as well, with resolution levels being limited only by the time required for signal averaging.



Stable Preload Provides Wide Range Trimming To DC-DC Converter (194 KB - PDF)