CO2 sensor
First Claim
1. A sensor for the measurement of carbon dioxide within a flow of air being input to at least one measuring cell (1) connected to at least one electroacoustic element (2,3) for transmitting and receiving airborne acoustic waves within said measuring cell (1) characterised in that at least one measuring signal is generated and being a monotonous function of the propagation velocity of said waves, and an indirect measure of said carbon dioxide concentration, said sensor including at least one automatic offset correction functionality for compensation of undesired offset variations of said measuring signal and wherein said offset correction functionality is based on the measurement or calculation of the average measuring signal, or extreme values calculated during a period of time, being shorter than the time lapses of said undesired offset variations.
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Abstract
A sensor for the measurement of carbon dioxide concentration within an air flow being input to a measuring cell (1) connected to at least one electroacoustic element (2, 3) for transmitting and receiving airborne acoustic waves within the measuring cell (1). The output signal of the sensor corresponds to the propagation velocity of these waves and an indirect measure of carbon dioxide concentration, with an automatic offset correction functionality for compensation of undesired offset variations of the signal, caused by temperature or humidity variations. Preferably, an accumulating function for minimizing the influence of the offset variations is included, which for humidity variations may consist of a material with high porosity and surface density of polar molecular groups. Temperature control of the inner sheath (4) is effected by a temperature sensor (11), a resistive heating element (12) in good thermal contact with the inner sheath (4), and a control circuit (13).
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Citations
9 Claims
- 1. A sensor for the measurement of carbon dioxide within a flow of air being input to at least one measuring cell (1) connected to at least one electroacoustic element (2,3) for transmitting and receiving airborne acoustic waves within said measuring cell (1) characterised in that at least one measuring signal is generated and being a monotonous function of the propagation velocity of said waves, and an indirect measure of said carbon dioxide concentration, said sensor including at least one automatic offset correction functionality for compensation of undesired offset variations of said measuring signal and wherein said offset correction functionality is based on the measurement or calculation of the average measuring signal, or extreme values calculated during a period of time, being shorter than the time lapses of said undesired offset variations.
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9. A sensor for the measurement of carbon dioxide within a flow of air being input to at least one measuring cell (1) connected to at least one electroacoustic element (2,3) for transmitting and receiving airborne acoustic waves within said measuring cell (1) characterised in that at least one measuring signal is generated and being a monotonous function of the propagation velocity of said waves, and an indirect measure of said carbon dioxide concentration, said sensor including at least one offset correcting unit for compensation of undesired offset variations of said measuring signal, and wherein said offset correction correcting unit comprises a signal accumulating circuit (16), and a differential amplifier (17).
Specification