Sulfur hexafluoride (SF6)‎ trace gas sensing using modulated CO2 laser beam

Abstract EN

Sulfur hexafluoride gas (SF6) is a very important in high voltage equipment as a spark arrestor medium for switch gear assemblies.

Laser-based Photo-Acoustic (PA) technique has been used to monitor the traces of SF6 leaks in the surrounding atmosphere.

This technique is based on inducing acoustic waves in the gas which is stimulated by a modulated (CW) CO2 laser beam of 10.6μm wavelength, 1.0 to 2.5W power and power modulation frequency of 1365 to 10920Hz (1st to 8th harmonics).

A cylindrical acoustic resonator of 50mm length and 4.5mm diameter is used, with a miniature microphone mounted at its midpoint to detect the sound waves.

A sound monitoring computer software (Sound Card Oscilloscope V4.1) has been used to capture and record the sound waves and their frequency spectrums.

Experimental results revealed that significant acoustic signal can be detected even at trace concentration, this is attributed to the high absorption of the CO2 laser radiation by SF6 gas.

Also, it conforms very well to the laser modulation frequency applied to the resonator, with a tendency to oscillate at higher harmonics when higher concentrations of SF6 exist within the gas mixture.

The strongest line of oscillation has been statistically found to be the 4th harmonic (5460Hz).