Patent ID: 7635845

Claim:
An IR sensor, especially a CO 2 sensor, having a filter arrangement, downstream of which there is arranged a detector arrangement, and an evaluating device which is connected to the detector arrangement, the filter arrangement having a first filter and a second filter, which are configured as bandpass filters and each have a passband and of which the first filter allows passage of a predetermined IR band and the second filter does not, and the detector arrangement having a first detector and a second detector, each of which is associated with one of the first filter and the second filter, the passband of the second filter being arranged within the passband of the the first filter and the evaluating device forming a difference of signals of the first detector and the second detector, wherein the first filter and second filter are formed by filter elements in series, one filter element being the same for both the first filter and the second filter and defining a common cut-off wavelength and the evaluating device normalising the difference of signals of the first detector and the second detector to the signal of one of the first detector and the second detector.