| 摘要 |
X-ray gauges for measuring the thickness of a material or a coating on a substrate lose their original accuracy due to variations in the high voltage supply of the X-ray tube, so that it is often necessary to perform a complete recalibration to reestablish the accuracy of measurement, especially if the X-ray source has to be replaced. This complete recalibration or "curvefit" requires a large number of samples or standards, is time-consuming and cumbersome. A calibration apparatus in an apparatus for measuring the thickness of a layer or a coating on a substrate is described, employing only two standards, comprising a generator of X-ray radiation (1) arranged to be directed towards a layer (3) the thickness of which is to be measured, a detector of radiation (2), arranged to receive radiation in the form of an output function of the thickness of a layer being measured, and computing means for measuring intensities of the radiation from the layer, with the layer absent, with a sample layer of a first predetermined thickness, with a sample of a second predetermined thickness and with a sample having a thickness which produces the same effect as a sample of infinite thickness, the computing means calculating a calibration ratio from at least some or of all of the measured radiation intensities representing the values of the said predetermined sample thicknesses and means for maintaining the calibration ratio at a fixed value by varying the energy of the beam of X-ray radiation. |
