Patent ID: 6061141
Filing Date: 2000-05-09
Classification: G01N

Abstract:
A method of increasing the sensitivity of detecting the presence of a predetermined first vapour of a predetermined threshold concentration having a first main absorption peak in a monitored area in optional presence of a second vapour having a second, yet close, main absorption peak, the method comprising the steps of:(a) exposing gas at the monitored area to radiation at wavelengths at least covering and surrounding from both sides said main absorption peaks of the vapours;(b) simultaneously sensing said radiation after passing via an open path through said gas by three independent sensors including a signal sensor, a reference sensor and an additional sensor identical to said signal or to said reference sensor, each of said three sensors including a radiation sensing element, wherein said signal sensor further includes a first optical filter passing wavelengths covering said first main absorption peak, yet substantially blocking wavelengths from both sides said first main absorption peak and wavelengths covering said second main absorption peak, whereas said reference sensor further includes a second optical filter passing wavelengths surrounding from both sides said first main absorption peak, yet substantially blocking wavelengths covering said first and second main absorption peaks; and(c) comparing signals obtained from said three sensors for determining a presence or absence of the first vapour of the predetermined concentration in said gas.