| 摘要 |
962,703. Infra red gas analysers. LEESONA CORPORATION. June 22, 1962 [June 26, 1961], No. 24209/62. Heading G1A. A system for detecting contaminants in the atmosphere comprises an infra-red source 10, means such as a chopper wheel 12 for periodically interrupting the rays from the said source, detector means 34 including an electrical system for receiving the rays and translating them into electrical signals, and a filter chopper 28 comprising a filter element movably mounted relative to the path of the rays between the source and the detector means and including means for moving the element of the chopper 28 into and out of the path of the rays at a sub-harmonic frequency of the frequency at which the chopper wheel 12 interrupts the rays. In the embodiment shown infra red rays from the source 10 are chopped by the wheel 12 to become a series of pairs of ray pulses 40, 41 (Fig. #2a) which are reflected by mirrors 16, 18 and 20 and are transmitted through filters 22 and 24 to) the mirror 26 and from there through a filter 32 to the detector 34. Assuming that the chopping frequency of the wheel 12 is twice that of the filter chopper 28 two complete source chopping cycles occur when the filter of the chopper 28 is interposed in the beam of rays and two while it is removed, the movements of the chopper 28 and the wheel 12 being synchronized through a mechanical linkage 30. If the chopper 28 were to pass a beam from a constant infra-red source (Fig. 2b) the amplitude of the signal 43 from the detector 34 when the filter was out of the beam would be a function of all the response bands of the detector 34. When the filter is in the beam the amplitude of the signal 45 represents all the response bands of the detector up to the cut off wavelength of the filter. Because of this wavelength only the signal 43 includes the atmospheric contaminant band. When the bands absorbed by normal atmospheric contaminants such as carbon dioxide and water are removed by the filters 24 and 22 respectively the ratio of the signal 43-45 should be constant if none of the atmospheric contaminant under investigation is present. With the chopper wheel 12 and the filter chopper 28 operating in synchronism the output of the detector is of the form shown in Fig. 2C. This signal is fed through a pre-amplifier and amplifier to a synchronous rectifier or switch (Fig. 3 not shown) synchronized with the chopper 28 to separate the signals A and B. These respective signals are then fed by separate conductors to a switch where they may be connected to a difference amplifier for initial optical alignment of the apparatus or to a ratio amplifier connected to a meter which may be calibrated to indicate directly the concentration of atmospheric contaminant. The detector used may be a thermal detector, a thermistor, a gas filled Golay cell or a pneumatic/ capacitor detector. |
