Patent ID: 7382819

Claim:
A method of manufacturing closed, filled containers transparent to laser light, the pressure of a gas species therein being known, comprising: manufacturing closed, filled containers transparent to said laser light; conveying said containers in one direction into a monitoring station; providing at least one reference container transparent to said laser light; providing differently than in said one direction said at least one reference container to be exposed to transmission of said laser light; exposing said containers in said monitoring station and said at least one reference container to said transmission of said laser light; periodically modulating the wavelength of said laser light during said transmission over a wavelength band including at least one absorption line of said gas species; optoelectronically converting, said periodically modulated and transmitted laser light, thereby generating a monitoring signal from transmission respectively through said containers and a reference signal from said transmission through said at least one reference container; generating an output signal in dependency of said monitoring signal and said reference signal, and evaluating said output signal as a signal indicative of pressure of said gas species prevailing in a respective one of said containers and assigning said pressure to said one container.