Abstract: An infrared gauge for, and a method of, measuring a parameter of a sample, e.g.

Abstract: A calibration standard for use with an infrared optical absorption measurement gauge having an assembly with an optical interference filter (22) and one or more optical elements. The interference filter has spectrally selective properties so that all but a selected spectral band is reflected by the filter towards the detectors of the gauge. The transmitted band is selectively absorbed by the optical element(s) which are spectrally unselective and also directed towards the detectors of the gauge. The position and strength of the selected band can thereby be adjusted to simulate an absorption spectrum, i.e., a corresponding spectral band which is characteristic of the absorption spectrum of a material under measurement. The standard is used to calibrate the absorption measurement gauge.

Abstract: A sampling system includes a plurality of sensing means (3) mounted on one or more beams (2) which reciprocate, over a moving web (1) of material. The sensing zones of adjacent sensing means (3) trace out scanning paths which periodically overlap in a sampling region. One of the sensing means (primary) scans over a known reference to update its calibration periodically or continuously and this is transferred to the other sensing means (secondary) effectively via the travelling material (due to the overlap). Calibration is performed by signal processing means, storing and comparing monitoring signal levels or corresponding digital values derived at positions of overlap and making computations for the purpose of calibration. With sufficient overlap of the scanning paths any one of the sensors can be made redundant. Alternatives include sensing means which move relative to other sensing means as well as rotary arrangements.

Abstract: In a method wherein sets of measured values of the intensity of electromagnetic radiation, which has been subject to optical interference, absorption or scatter by a sample, are correlated with different sets of known values derived from either a model of the optical properties of the sample, or from an analogue technique, correlation is by means of either a zero dependent correlation function, or a normalized residual function. Both functions are unaffected by gain factors, thereby avoiding any need to determine and to maintain absolute sensitivities of optical detectors; provide greater variation of correlation than with techniques employing a conventional correlation coefficient, thereby increasing the precision with which the optimum correlation can be determined, especially when either the measured value, or known values are subject to error; enable the method to be carried out with only two radiation components; and can enable a reduction in computing time.

Abstract: In the method and apparatus, optimum correlation between measured and known values of transmittance or reflectance determines the property or identity of a sample. Three or more discrete radiation components can be selected which are transmitted or reflected by relatively different amounts due to interference, absorption or scatter, thereby enabling fewer radiation components to be used to provide an accurate result. The known values can be derived by analogue or digital techniques, the digital technique employing a model or models taking account of absorption, interference and/or scatter. Techniques are disclosed for reducing computing time by range ajustment, identification of a zero correlation value in a differential function of the model or models and computation of correlation coefficients for two or more groups of radiation components.

Abstract: The calibration standard is attached to a sensing head of an infrared absorption gauge for the purpose of calibrating the gauge. The calibration standard includes spectrally selective absorption means having a spectrum closely resembling that of a substance to be measured, such as water sorbed onto a paper sample. The calibration standard also includes optical means for returning infrared radiation, which has passed through the absorption means, to the absorption gauge substantially along the same path as would normally be followed by the radiation reflected from the sample in the absence of the standard. The spectrally selective absorption means is preferably made of anhydrous material, such as glass containing a rare earth substance, or polypropylene, which is stable. The optical means may include diffusing means and a reflective plane.