All sensing is using physical measurement of phenomena. Sensor developments have greatly influenced by the progress in solid state electronics. Solid state electronics and chip technology have assisted in miniaturization of various sensors. For example, gas chromatography column is available on a small silicon wafer. Human judgment is always the hardest thing to duplicate in any machine. However, advantages of in-line sensors include real-time analysis and process control, improved product uniformity and quality, and conversion of batch operations to semi-continuous or fully continuous processes.