Infrared laser detector employing a pressure controlled differen

Details Infrared laser detector employing a pressure controlled differen Infrared laser detector employing a pressure controlled differen

1975-04-28

1977-04-19

Smith, Alfred E.

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

G01J 342

Patent

active

040190560

ABSTRACT:
An infrared laser absorption spectrometer is disclosed wherein a pair of detector cells are disposed serially along the laser beam path. The laser beam is modulated to produce a modulation of the absorption by the sample materials in the two cells. Modulated absorption by the samples produces an acoustic wave in each cell which is detected by a suitable microphone and subtracted so as to produce a difference signal corresponding to the difference in infrared absorption between the two cells so that undesired background effects common to both cells are cancelled. A pressure controller, which is responsive to the pressure difference between the sample pressure in the two cells at a frequency substantially below the beam modulation frequency is employed for controlling the pressure differential. In one embodiment the pressure controller includes a compliant membrane partitioning the two cells so that the membrane may move so as to equalize the pressures. In a second embodiment, deflection of the diaphragm of a differential microphone coupled into both cells is employed to derive an output utilized to control either the flow through the cells and/or the volume of the respective cells to control the pressure difference between the cells.

REFERENCES:
patent: 3005097 (1961-10-01), Hummel
patent: 3105147 (1963-09-01), Weilbach et al.
patent: 3727050 (1973-04-01), Kerr
patent: 3793525 (1974-02-01), Burch et al.
patent: 3820901 (1974-06-01), Kreuzer
patent: 3893771 (1975-07-01), Bell

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