Miniature Infrared Gas Sensor for Carbon Dioxide Cirius2

Features
1) Temperature compensated detectors
2) Sensing ranges: 0-5000ppm Carbon Dioxide to 0-5% volume Carbon Dioxide
3) All metal construction
4) Small internal volume
5) ‘Light locked’: not affected by external illumination
6) Low power
7) Active and Reference signal outputs
8) Embedded thermistor temperature sensor output
9) Wide operating temperature range
10) Fast response
11) Immunity from ‘poisoning’
12) Fail safe operation
13) Electrically isolated housing

Description and Operation

The Cirius range of sensors use the non-dispersive infrared method to detect the presence of gases. The sensors contain an infrared radiation source, a dual element infrared detector and a unique optical waveguide into which gas diffuses. The dual element infrared detector responds to changes in incident radiation and to operate the sensor the infrared source should be pulsed with a duty cycle of 50% at a frequency typically between 2Hz and 4Hz. The sensor produces outputs for active wavelengths, which are modified by the presence of target gas, and for reference wavelengths, which are not modified by the presence of target gas. These outputs consist of a small AC signal in sympathy with the source pulse that is superimposed on a DC voltage pedestal. The sensor also provides a measure of internal temperature via an embedded thermistor. The sensor requires a voltage supply to operate the infrared detector and the connections to the sensor follow the industry standard 7 pin format. 

To operate the sensor it must be connected to a suitable circuit that provides the source drive and extracts the small AC signals from the DC voltage pedestal. The circuit must amplify the small AC signals, extract a value from them and treat the results to provide a linear output related to gas concentration. The temperature output from the sensor should be used to apply temperature compensation in order to achieve the full performancespecification.