Temperature dependence of a piezoceramic transducer electric impedance

Abstract

The paper presents the possibility to evaluate temperature by measuring the piezoceramic transducer’s electric impedance and capacitance. The temperature-dependent electric impedance and capacitance characteristics were investigated within the range of 20…140° C for various types of piezoceramic transducers that are used in ultrasonic flow meters. The results of the investigation show that for all the types of the investigated piezoceramic transducers a common temperature-dependent behavior of an electric impedance within the frequency ranges below the resonance frequency (from 0,5 MHz to 1MHz) which is characterized in linear decreasing of the electric impedance about 1,5..2 times when temperature of piezoceramic discs increases from 20° to 140° C degrees has been found. The temperature measurement sensitivity increases with decreasing of the frequency at which the transducer electric impedance is measured and has been found as the highest for non-diced piezoceramic transducers having a matching layer with a lower acoustic impedance. This effect can be applied in ultrasonic flow, level or other meters for correction of the temperature-dependent systematic errors without applying any additional temperature measuring channels and temperature sensors.