Alf Püttmer

Application of ultrasonic sensors in the process industry

Continuous process monitoring in gaseous, liquid or molten media is a fundamental requirement for process control. Besides temperature and pressure other process parameters such as level, flow, concentration and conversion are of special interest. More qualified information obtained from new or better sensors can significantly enhance the process quality and thereby product properties. Ultrasonic sensors or sensor systems can contribute to this development. The state of the art of ultrasonic sensors and their advantages and disadvantages will be discussed. Commercial examples will be presented. Among others, applications in the food, chemical and pharmaceutical industries are described. Possibilities and limitations of ultrasonic process sensors are discussed.

SPICE model for lossy piezoceramic transducers

A transmission line equivalent circuit for piezoelectric transducers has been modified to provide modeling of lossy piezoceramic transducers. A lossy transmission line is used to model the mechanical losses. The equivalent circuit parameters are derived from analogies between electrical transmission lines and acoustic wave propagation. Implementation of the equivalent circuit model in SPICE is shown. Simulations and measurements in the time and frequency domain of a low-Q material and a multilayered ultrasonic sensor using a low-Q piezoceramic transducer are presented.

Ultrasonic sensors for process monitoring and chemical analysis: state-of-the-art and trends

Abstract Ultrasonic sensors are used in a large variety of ways. New fields of ultrasonic: sensor and ultrasonic sensor system applications are process monitoring and control, automotive techniques and chemical analysis. These applications have enjoyed a rapid increase of interest in recent years. The development of new ultrasonic sensors or systems was and is essentially accelerated by the progress in electronics, by new piezoelectric materials, by exploitation of new technologies and by the need for new or more accurate analysis methods in many industrial branches. A review of ultrasonic sensors based on piezoelectric materials and resonators is presented. First, the physical background for ultrasonic wave propagation and corresponding technical applications is given. A definition of the ultrasonic sensor system is introduced later because an ultrasonic sensor alone makes no sense. For an efficient use of this sensor principle, a well-developed transmitter and receiver electronics and intelligent data-acquisition electronics are necessary. Secondly, it is shown that ultrasonic sensors can be divided into four groups depending on how the ultrasonic signal has been changed on its path during propagation or the transducer properties are changed by interaction with the surroundings. The present state of established sensors for flow, distance and level is discussed. Ultrasonic sensors for process monitoring are described. New application fields for these sensors can be predicted. Finally, ultrasonic microsensors are introduced. A description of their state-of-the-art and application examples are given. To conclude, the use of new technologies for the manufacture of miniaturized ultrasonic sensors and future developments are discussed.

Ultrasonic density sensor for liquids

This paper presents a new ultrasonic density sensor for liquids. It unifies high accuracy with high durability and is suitable for a wide range of tube diameters. The sensor comprises a transducer consisting of a piezoceramic disk mounted between two reference rods of quartz glass. Additionally, a second transducer is used as a sound receiver. The density is obtained from the reflection coefficient of ultrasound at the interface between the quartz glass rod and the liquid, and the transit time of sound between this interface and the second transducer. Parameters like a high long term stability and accuracy of /spl plusmn/0.2% were achieved by an internal acoustic reference measurement and a high signal-to-noise ratio. The latter was gained by using the sound radiated from the rear side of the piezoceramic disk as the reference. Advantages of the new sensor are discussed and experimental results are given. Applications of the sensor comprise concentration measurement and ultrasonic mass flow measurement.

Improved ultrasonic density sensor with reduced diffraction influence

The density of liquids can be measured with ultrasonic techniques. An important factor limiting the accuracy of the measurement is the effect of diffraction of acoustic waves in the transducer. This paper presents a method to minimize such effects. A simple geometric model is used to analyse the contributions of plane waves and diffraction waves as a function of the sensor geometry. Calculations using the model lead to an optimized sensor geometry where diffraction waves do not interfere with the measurement signals. To demonstrate the fundamental improvement of accuracy, selected measurements of optimized and non-optimized sensors are compared.

Ultrasonic density sensor—analysis of errors due to thin layers of deposits on the sensor surface

Abstract The density of liquids can be measured with ultrasonic techniques. Such sensors determine the reflection coefficient of ultrasound at the boundary between a reference material and the investigated liquid. An important question for application of these sensors is the influence of thin layers which may be deposited at the sensor–liquid interface. This article analyses the measurement errors of an ultrasonic liquid density sensor utilising simulation techniques.

Optimization of buffer rod geometry for ultrasonic sensors with reference path

Several applications of ultrasonic techniques are limited by the signal-to-noise ratio (SNR). Transducers in these applications usually operate in the pulse-echo mode. Many transducers, especially those for high temperatures, use buffer rods. Often a reference path is used to eliminate electrical and transducer drift. Interference of echo signals and noise causes errors of both amplitude and phase measurement of the detected echoes. In this paper we discuss the influence of major noise sources as a function of geometry and operating environment. The effects are studied using both experimental results and models. Although the results are applied to an ultrasonic density sensor operating in the pulse-echo mode, they are applicable to other pulse-echo mode transducers comprising homogeneous cylindrical buffer rods. This paper will show how the SNR of the density transducer was improved in a special time window from 34 to 72 dB by careful design.

High-accuracy measurement of pulse amplitudes for new applications of ultrasonic sensors

The paper presents a high-accuracy method to measure the peak-to-peak value of short pulses that are received by piezoceramic transducers, opening new applications for ultrasonic sensors. By employing a digital technique, 12-bit accuracy is achieved for a transducer with 2 MHz centre frequency. In the first step the signal is digitized; in the second step a fast digital comparator determines the peak-to-peak value. The complete digital part could be integrated in a single integrated circuit.

P3F-6 Acoustic Emission Based Online Valve Leak Detection and Testing

A measurement principle for quantitative control valve seat leakage classification, in accordance with ANSI/FCI 70-2 and IEC 60534-4, based on the acoustic emission measurement in the ultrasonic range is presented. The advantage of this method is that the leakage test can be performed on-site without having to disassemble the valve. The valve has to be closed for this test. If the valve is occasionally closed under normal operating conditions, the test can also be done on-line.

Ultrasonic density sensor - higher accuracy by minimizing error influences

The density of a liquid can be determined from the acoustic parameters speed of sound and acoustic impedance. Unwanted deposits in pipelines and on sensor surfaces or gas bubbles in the fluid are common problems in industrial applications of ultrasonic sensors. Results of experiments and simulations of thin layer deposits show a correlation of the time delay of the reflected echo signal and the product of layer impedance and time of flight through the layer. This can be used for layer detection and error correction. The influence of gas bubbles on frequency and amplitude of the speed of sound sensor signal is shown. A correction of the speed of sound measurement error is presented, in which signal reconstruction and processing is used.