| 摘要 |
1,271,439. Detecting moisture in paper. MEASUREX CORP. Jan. 15, 1970 [Feb. 17, 1969], No. 2077/70. Heading G1A. An apparatus for measuring the amount of a substance in a base material (e.g. moisture in paper) comprises a radiation source that emits first and second spectral bands which are subsequently reflected from or transmitted through said material, the first spectral band lying outside and the second spectral band lying inside a resonant absorption band of the substance; first and second detector means responsive to the intensities of said first and second spectral bands respectively and control means for maintaining constant the received intensity of said first spectral band by controlling the intensity of said radiation source. In an embodiment Fig. 9 for measuring the amount of water present in a moving web of paper 10 which is being scanned by a source 11 and detector 12 which move transversely to the direction of motion of the web 10, an infrared source S projects radiation on to web 10 by means of mirror M1 and lenses L1 and L2. The radiation transmitted is received by detector 12 and is split up by semi reflective mirror M2, Fig. 10, and filters (18), (19), Fig. 3 (not shown), into the two aforementioned spectral bands which are focused by means of lenses L3, L4A, L5A and L3, L4B, L5B on to photo-cells D1 and D2 respectively. Photo-cell D2 is part of a bridge arrangement 32, Fig. 5, also comprising three equal resistances R, an oscillator 31 and operational amplifiers 27, 28. The bridge arrangement 32 is such that subtract amplifier 29 provides a signal which is proportional to the variations of the resistance of D2 from the resistance R (the resistance R being equal to the resistance of the photo-cell at a predetermined working point on the detector's characteristic curve). The signal from subtract unit 29 is fed via amplifier 33, phase detector 34 and integrator 37 to lamp drive amplifier 38 which drives the radiation source S; thereby controlling the intensity of the sources by means of the 'error' signal produced by the bridge arrangement 32. The photo-cells D1, D2 are also included in a ratio bridge 52, Fig. 5, which comprises an inverting operational amplifier 30 a unity gain buffer amp 54 and an oscillator 31 connected up so that the output of subtract unit 53 is proportional to the ratio of resistances of the two photo-cells, which is indicative of the absolute moisture content of the web 10. The output signal of the subtract unit 53 is fed via an I. F. strip and a synchronous demodulator 57 to a data processor. In order to use the detectors at their optimum . operating impedance with different kinds of paper, standardization means comprising alternators A1, A2 are employed.
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