The Regenerative Digital Transducer (RDT): A New Active Microwave Field Sensor for Industrial Measurements and Control

Abstract

A regenerative digital transducer (RDT) with an active linear response is described. The RDT can be operated in a contact or non-contact mode for moisture measurements in dielectric webs and in liquids or oils flowing inside dielectric pipes. The design is adapted for industrial measurements and on-line control purposes. INTRODUCTION Passive transducers have been used in the past for the measurement of non-electrical parameters such as moisture content and metal strip thickness [1-3]. More recently active transducers have been introduced for similar measurements employing either closed [4][5][6] or open [7-9] cavity resonators. This paper will describe the design of the Regenerative Digital Transducer and some results of measurements obtained in the food and paper industries. The RDT uses a transmission type, low frequency (less than 500 MHz) far field resonator in an external feedback loop of a transistor amplifier such that direct frequency measurements with inexpensive and accurate counters are possible. Figure 1 shows a typical block diagram of the RUT in use with four measuring systems. In system 1 the frequency is read directly from a counter and the observation is manually recorded. This is the simplest and most inexpensive ar-PROCESS PROCESS rangement. In system 2 the coun-