| 摘要 |
An infrared web moisture sensor which is substantially temperature and basis weight insensitive comprises a source of infrared radiation for directing an infrared beam through the web and an infrared detecting unit on the other side of the web which measures the transmission of the infrared beam through the web at three separate wavelength regions. The transmission in the first wavelength region is primarily sensitive to the moisture content of the web. The transmissions in the second wavelength region is less sensitive to the moisture content. The transmission in the third wavelength region provides an indication of the web temperature. Temperature insensitivity is achieved by selecting the temperature response of a measurement band pass filter and a reference band pass filter based on the maximum basis weight and the maximum moisture content of the web and compensating for any remaining temperature sensitivity with a temperature correction band pass filter. Signals indicative of the transmission of infrared through the web in each of these regions are digitized and fed to the process control computer for the paper mill. The computer combines the values of the digitized signals, using an empirically derived equation, to produce a value indicative of the percentage of moisture in the web which value is not affected by changes in web temperature. The process control computer utilizes this result to control devices which selectively and moisture to portions of the web or selectively dry portions of the web, thereby producing a web having a desired moisture content profile. |
