Photoacoustic sensor with replacement gas and detection process using such a sensor

A photoacoustic sensor in accordance with claim, 8, further comprising a selection unit for use by a person, wherein:

• the selection unit is configured to detect a selection of a target gas to be detected;
• a respective computer-evaluable concentration relationship is stored in the memory for at least two different differing target gases, which can be selected by means of the selection unit;
• and
• the analysis unit is configured to determine the concentration of the selected target gas in the sample chamber and to use for this the concentration relationship that is stored in the memory for the selected target gas.

A process for detecting at least one target gas in an area with the use of a photoacoustic sensor, which photoacoustic sensor comprises a radiation source, a sample chamber, a detection chamber and an acoustic receiver, wherein a target gas wavelength range, in which a target gas to be detected or each target gas to be detected attenuates an intensity of electromagnetic waves is predefined, wherein the detection chamber is fluid-tightly sealed against an area around the detection chamber and is free from the target gas to be detected or each target gas to be detected and is filled with a replacement gas, the process comprising the steps of:

• bringing about a state of the sensor in which a gas sample flows from the area into the sample chamber;
• with the radiation source, emitting electromagnetic waves in a direction of the sample chamber such that emitted electromagnetic waves pass through the sample chamber and the detection chamber, wherein a wavelength range of the emitted electromagnetic waves comprises the target gas wavelength range and during passage of the emitted electromagnetic waves through the detection chamber, the electromagnetic waves elicit in the detection chamber an acoustic effect, which is correlated with the intensity of the electromagnetic waves passing through the detection chamber;
• with the acoustic receiver, measuring an indicator of the acoustic effect elicited in the detection chamber by the electromagnetic waves;
• and
• with the acoustic receiver generating a signal for the measured indicator of the acoustic effect, wherein:
• at least at an ambient temperature between 10° C. and 40° C., the replacement gas is chemically more inactive than the target gas to be detected or each target gas to be detected and a spectral overlap between the target gas to be detected or each target gas to be detected and the replacement gas is above 0.2 in the target gas wavelength range;
• and
• the spectral overlap between the target gas and the replacement gas is an indicator standardized to a range between 0 and 1 for a congruence between the spectral response of the transmission of the target gas and the spectral response of the transmission of the replacement gas in the target gas wavelength range.