Accurate ratio measurement using phase-detector - gives method of measuring physical parameters accurately normalized with respect to standard

摘要

A phase measurement bridge arrangement is used by which various physical parameters may be measured accurately in the form of a ratio. The example described is the measurement of the translucence of some medium compared with that of air. Basically, a light beam is modulated at some unspecified frequency and is directed via a set mirrors of which one is semi-reflecting, along two paths to two photoelectric cells. One path is through air, and the other through the medium concerned. The output sinusoidal signals from these photocells are processed by integrators, adders and inverters constructed of liner amplifiers, to produce a signal of which the phase is a measurement of the ratio of the amplitude of the two received signals.