Niels Hoppe

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.

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.

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.

Ultrasonic sensors for process industry

Continuous process monitoring in gaseous, liquid or melted media is a fundamental requirement for process control. Beside 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. Applications in the food, chemical, pharmaceutical industry and other are described. Possibilities and limitations of ultrasonic process sensors are discussed.

Ultraschall-Dichtesensor für Flüssigkeiten – Eigenschaften und Grenzen (Ultrasonic Density Sensor for Liquids – its Potentials and Limits)

Die On-line-Dichtebestimmung von flüssigen Medien ist wichtig für die Automatisierung von Prozessen in der chemischen, pharmazeutischen und Lebensmittelindustrie. Ein neu entwickelter Ultraschallsensor bietet eine Alternative zu den hauptsächlich am Markt vorhandenen Coriolis- oder Biegeschwingermessprinzipien. Besonders bei größeren Rohrquerschnitten und dem Auftreten von Gasblasen sowie starken Temperaturgradienten im fließenden Medium werden die Vorteile dieses Sensors sichtbar. Die Untersuchungen zeigen, dass der Sensor neben einer guten Langzeitstabilität auch gute dynamische Eigenschaften aufweist. Betrachtungen zur chemischen Beständigkeit und zum Einfluss von Ablagerung und Gasblasen runden die Untersuchung der Eigenschaften ab.

Low noise design of ultrasonic transducers

Several industrial applications of ultrasonic techniques are limited by the signal-to-noise ratio (SNR). Examples include NDE or process monitoring. Transducers in these applications usually operate in the pulse-echo mode. Several transducers, especially those for high temperatures, use buffer rods. Interference of echo signal and noise causes errors of both amplitude and phase measurement of the detected echoes. This work aims to discuss the influence of major noise sources as a function of transducer materials, geometry, construction and operating environment. The effects are studied with the help of both experiments and models. The results are applied to an ultrasonic density sensor operating in the pulse-echo mode, however are applicable to any pulse-echo mode transducer comprising cylindrical buffer rods. The paper shows how the SNR of the density transducer was improved by careful design to 72 dB.

Optimization of buffer rod geometry using MATLAB

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. Several transducers, especially those for high temperatures, use buffer rods. Interference of the echo signal and noise causes errors of both amplitude and phase measurement of the detected echoes. In this work we discuss the influence of major noise sources as a function of transducer materials, geometry, construction and operating environment. The effects are studied using both experiments and models. Although the results are applied to an ultrasonic density sensor operating in the pulse-echo mode, they are applicable to any pulse-echo mode transducer comprising cylindrical buffer rods. This paper will show how the SNR of the density transducer was improved by careful design to 72 dB.