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Gas concentration detection method and device

A gas detection and gas technology, which is applied in the field of low-cost infrared gas detection and can solve problems such as errors

Inactive Publication Date: 2007-02-07
IR MICROSYST
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Problems solved by technology

In the case of high gas concentrations, the accuracy of the measurement is limited by errors affecting the accuracy of the DC laser current of the modulated reference signal at frequency f

Method used

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  • Gas concentration detection method and device
  • Gas concentration detection method and device

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Embodiment Construction

[0025]In the following, the signal processing is described in detail as long as it differs from the prior art mentioned in WO 2005 / 026705 A1. The content of this document is incorporated by reference as far as signal processing is concerned, which signal processing may not be described in this specification.

[0026] As already described and already mentioned in WO 2005 / 026705 A1, the laser source is operated with a DC current such that its wavelength corresponds exactly to the center of the gas absorption line. This current is constantly modulated with frequency f and amplitude such that the wavelength of the laser light completely scans the gas absorption line during each cycle by the corresponding AC modulation signal. figure 1 Shows as a function of time, reflected in the initial optical signal S 0 The laser output in which the detection region having the gas to be determined receives the laser output, and figure 2 shows the light intensity as a function of time, which ...

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Abstract

The gas detector device comprises at least a VCSEL source and at least a light sensor for detecting a light beam having passed through a sample chamber containing a given gas to be detected. The detection signal of the sensor directly provided to or is time derivated by an electronic derivator and then provided to respective lock-in amplifiers in order to generate a two different 2f-detection, f being the frequency of a wavelength modulation of the source, and thus to provide two corresponding measuring signals the division of which gives a precise value of the gas concentration. The invention uses at least a first modulation reference signal at twice and a second modulation reference signal at twice of the modulation frequency of the laser source. Providing at least a first 2f modulation reference signal has advantages over the prior art, because by using such a reference modulation signal it is possible measure the absolute intensity and therefore to receive the same result at different temperatures or at mode hopping of the laser. A further advantage is that the measurement accuracy is independent from the gas concentration.

Description

technical field [0001] The present invention relates in particular to low cost infrared (IR) gas detection as disclosed in WO 2005 / 026705 A1. Background technique [0002] The gas detection method and gas detector device as described in this prior art publication are based on the formation of a vertical cavity surface emitting laser (VCSEL, Vertical Cavity Surface Emitting Laser) or distributed feedback (DFB, Distributed Feed Back) laser by wavelength modulation source, and the gas detection method and gas detector apparatus exploit the fact that the modulation of the wavelength is directly related to the modulation of the output intensity of the laser source. The intensity of light that has passed through the gas volume and is incident on the detector thus shows a first modulation related to the laser source intensity and a second modulation related to the gas absorption as the wavelength is scanned across the gas absorption line. Therefore, known detection methods and dev...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N21/35G01N21/39
CPCG01N2201/0691G01J3/433G01N21/39G01N21/3504
Inventor B·维林M·科利A·塞费尔特
Owner IR MICROSYST
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