Dynamically standardized radiant energy method and apparatus for plural channel gain independent material property measurement

摘要

A method and apparatus for determining a property of a material (10) utilizes a source (28) of measuring radiation and reference radiation, a measuring information channel including a detector (30) for the measuring radiation, and a reference information channel including a detector (32) for the reference radiation. A channel-monitoring radiation is also produce. In a standardizing mode, a monitor-standardization response (M. sub.11 or R. sub.11) is derived from each of the two channels while passing monitoring radiation to both detectors and a source- standardization response (M.sub.12 or R.sub. 12) is derived from each of the two channels while passing measuring radiation to the measuring detector and passing reference radiation to the reference detector. In an operating mode, an operation-monitoring response (M.sub.21 or R.sub. 21) is derived from each of the two channels while passing monitoring radiation to both detectors and a material-condition response (M.sub.22 or R.sub.22) is derived from each of the two channels while directing source radiation into the material and passing to the respective measuring and reference detectors measuring and reference radiation that has interacted with the material. By responding to the monitor- standardization responses, the source-standardization responses, the operation-monitoring responses and the material-condition responses, there is produced a material property response (at 164 or 166) that is effectively standardized and substantially independent of gain changes occurring in either one or both of the measuring and reference information channels. The example shows the measurement of moisture content in a traveling sheet of paper with infrared radiation at 1.4&mgr;, 1.8&mgr; and 1.9&mgr;.