Noise canceling detector
AssigneeSintef Tto AS
InventorIb-Rune Johansen
Life of this patent
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Abstract
The present invention relates to an optical gas detector for detecting a gas absorbing light at a known wavelength, wherein the gas detector comprises two essentially identical, parallel membranes defining a volume between them containing the gas to be investigated, and a modulated first light source emitting light at said known wavelength into said volume at a chosen frequency, the detector is adapted to detect relative movements between said membranes and said movements having a frequency corresponding to the rate or a multiple of the rate of said pulsed light source, and wherein the said volume has at least one opening allowing the gas to unrestricted flow or diffuse into said volume.
Claims13
A noise cancelling optical gas detector for detecting a gas absorbing light at a known wavelength, the optical gas detector comprising:
- two identical, parallel membranes defining a volume between them containing the gas to be investigated;
- a modulated light source emitting light at the known wavelength into the volume at a chosen modulation frequency;
- wherein the optical gas detector is adapted to detect movements between the membranes caused by the light absorption in the gas resulting in pressure fluctuations in the gas volume resulting in movements of said two membranes thus having identical opposite directions and having a frequency corresponding to the rate or a multiple of the rate of the modulated light source;
- wherein the gas volume allows the gas to flow or diffuse unrestricted into the volume;
- and
- wherein the movement detections are provided by using optical measurements adapted to monitor the distance between the two membranes.
An optical gas detector for detecting a gas absorbing light at a known wavelength, the optical gas detector comprising:
- two identical, parallel membranes defining a volume between them containing the gas to be investigated;
- a modulated light source emitting light at the known wavelength into the volume at a chosen modulation frequency;
- wherein the optical gas detector is adapted to detect movements between the membranes caused by the light absorption in the gas resulting in pressure fluctuations in the gas within the volume resulting in membrane and the movements of said two membranes thus having opposite directions and having a frequency corresponding to the rate or a multiple of the rate of the modulated light source;
- wherein the gas volume being allowed to unrestricted flow or diffuse into the volume;
- and
- wherein the movement detections are provided by using optical measurements adapted to monitor the distance between the two membranes
- wherein the movement detections provided by using optical interferometry
- wherein the distance is monitored optically by transmitting monitoring light in a direction perpendicular to the membranes, the membranes being partly reflective and at least one of the membranes being partly transparent to the transmitted light, thus providing a Fabry-Perot interferometer and by monitoring the transmitted or reflected intensity from the Fabry-Perot interferometer, and
- wherein a number of recesses are incorporating into at least one membrane, the depth of the recesses are optimized to give a chosen phase change in the transmitted and reflected light, so as to provide a correction to the monitored change in the distance between the membranes.
An optical gas detector for detecting a gas absorbing light at a known wavelength, the optical gas detector comprising:
- two identical, parallel membranes defining a volume between them containing the gas to be investigated;
- a modulated light source emitting light at the known wavelength into the volume at a chosen modulation frequency;
- wherein the optical gas detector is adapted to detect movements between the membranes caused by the light absorption in the gas resulting in pressure fluctuations in the gas within the volume resulting in membrane and the movements of said two membranes thus having opposite directions and having a frequency corresponding to the rate or a multiple of the rate of the modulated light source;;
- wherein the gas volume being allowed to unrestricted flow or diffuse into the volume;
- wherein the movement detections are provided by using optical measurements adapted to monitor the distance between the two membranes, and
- wherein the modulation rate and size of the membranes are chosen so that the wavelength of the generated vibration in the gas, depending on the sound velocity of the gas, is less than half the diameter of the membranes.
Dependencies are inferred from the claim text.