A CRDS (Cavity RingDown Spectroscopy) analyzer measures the time it takes light from a laser to reach the detector after it has traveled a distance of 100 km in the measurement cell (cavity) with higher reflection mirrors.
Setting the laser to a known absorption wavelength will absorb the light into the measurement cell (cavity).
When the laser is turned off, the intensity decreases faster when it is absorbed by the component to be measured in the measurement gas than when no absorption has occurred.
This time difference is a measure of the concentration of the gas in the matrix.
This measurement technique does not measure absorption but rather time, a physical constant. This eliminates the need to adjust the analyzer with calibration gases.
As a zero calibration, the analyzer performs an automatic check. This involves setting the laser to a wavelength at which no absorption occurs.
In addition, an occasional scan is required that verifies that the laser is still set at the maximum peak.
No calibration gas is required for either procedure.
