Assembly and method for measuring a substance concentration in a gaseous medium by means of absorption spectroscopy

An assembly for measuring a gas concentration by means of absorption spectroscopy, the assembly comprising;

• an IR light emitting thermal light source,
• a measuring cell with a gas mixture to be analyzed, the measuring cell having a gas inlet and a gas outlet configured flor flowing the measuring gas therebetween, the measuring cell defining a measuring path in which the IR light crosses the gas to be measured,
• one or more sensors,
• one or more bandpass filters upstream from the one or more sensors,
• an optical beam path comprising the thermal light source, the measuring cell including the measuring path, the one or more bandpass filters and the one or more sensors.
• a gas concentration measuring evaluation apparatus in communication with the one or more sensors to determine a concentration of the measuring gas as a result of attenuation of the IR light in the measuring cell,
• wherein the one or more bandpass filters comprises at least one measuring wavelength bandpass filter configured to transmit the IR light within a measuring wavelength range in which the gas to be measured absorbs IR light, and at least one reference wavelength bandpass filter configured to transmit IR light in a reference wavelength range in which the gas to be measured does not absorb IR light or only absorbs a slight amount in comparison to the measuring wavelength range,
• further wherein the thermal light source comprises an encapsulated micro-incandescent lamp with a light-generating coil disposed is in a substantially transparent capsule, the capsule being evacuated or filled with an inert gas, and
• wherein the measuring gas concentration is capnometric measurement of the proportion of CO2 in breathing air.