Infrared Sensor Application Note 4——————————download ：20276.pdf

INTRODUCTION
This application note gives guidance on the design of electronic circuits for use with SGX Sensortech infrared gas sensors. The information is provided for general advice and care should be taken to adapt the circuits to the particular requirements of the application. By following the recommendations of this application note, the user should be able to achieve excellent performance with SGX Sensortech infrared gas sensors. Figure 1 shows the outline block diagram of a typical gas detection system using an infrared gas sensor. The IR gas sensor contains a lamp which is pulsed at low frequency by a lamp drive circuit. The pulses of infrared radiation reflect internally to provide a long path through the target gas. Pyroelectric detectors (pyros) are used to
detect the change in infrared signal. The active pyro is sensitive to changes at IR wavelengths which are typically absorbed by the gas being detected. The reference pyro is sensitive to changes at a nearby IR wavelength which is not absorbed by the gas being detected.