Miniature Infrared Gas sensor for Hydrocarbons
Features:
Sensing ranges:0-100% LFL Methane,0-100% LFL Hydrocarbons and 0-100% volume Methane
All metal construction
Small internal volume
‘lightlocked’:not affected by external illumination
Low powed
Active and Reference signal outputs
Embedded thermistor temperature sensor output
Wide operating temperature range
Fast response
Immunity from ‘poisoning’
Fail safe operation
Zero maintenance
Electrically isolated housing
Descripting 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 extract 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 compensation in order to achieve the full performance specification. Technical support on implementation and application notes are available from Clairair Limited.
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