Abstract: An apparatus for measuring parameters, such as moisture content or basis weight, of a fibrous web, e.g. paper or non-wovens, comprises optical elements and a wavelength selection device for selectively directing a beam of electromagnetic radiation comprising wavelengths in at least the mid infrared (MIR) spectral range through the web; an element, such as a beam stop, arranged in the path of electromagnetic radiation emerging from the web, for separating directly transmitted from scattered electromagnetic radiation; a collector for collecting the scattered radiation; and at least one detector for detecting the scattered radiation collected by the collector.

Abstract: An apparatus for measuring parameters, such as moisture content or basis weight, of a fibrous web, e.g. paper or non-wovens, comprises optical elements and a wavelength selection device for selectively directing a beam of electromagnetic radiation comprising wavelengths in at least the mid infrared (MIR) spectral range through the web; an element, such as a beam stop, arranged in the path of electromagnetic radiation emerging from the web, for separating directly transmitted from scattered electromagnetic radiation; a collector for collecting the scattered radiation; and at least one detector for detecting the scattered radiation collected by the collector.

Abstract: An infrared absorption gauge includes a detector circuit including a detector for detecting electromagnetic radiation from a sample and for generating a signal representing the radiation received, and means for stabilizing a response characteristic of the detector to the radiation detected thereby, said stabilizing means having a GaAs diode for directing radiation at the detector and means for controlling the radiation source in dependence upon the signal generated by the detector. The stabilizing means thus acts as a negative feedback loop and seeks to maintain the overall illumination irradiating the detector (i.e. the combined illumination that is reflected back from the sample and that is emitted by the GaAs diode), at a substantially constant predetermined level, which tends to linearize and extend the frequency response of the detector to the radiation detected.