Measuring system for measuring the amount of dielectric in a web

Abstract

An instrument determines one or more physical properties, including dielectric, in a web or other material. A resonant cavity in the instrument resonates at a known band of frequencies. The instrument generates a constant frequency signal within the known band, divides the signal into a measuring signal and a reference signal. With the instrument proximate the web, the measuring signal is passed into the resonant cavity. A first fraction passes through the resonant cavity. incurring a phase shift. A second fraction is reflected from the cavity. The phase shift in the measuring signal is compared to the reference signal, and a first output signal is sent to a controller. The magnitude of the reflected signal is determined, and a second output signal is sent to the controller. Using the first and second output signals, the controller calculates a resultant property value (e.g. moisture content), using the combined values of phase shift and reflected power to cancel out the affect of distance of the e.g. moisture from the resonant cavity. The instrument can also determine length, speed of travel, and temperature of the web, and the controller can combine such measurements mathematically, determining the location in the web of, for example, given readings of moisture and temperature, as well as the general condition of the web.