[Magnetostrictive Depth Gauge]

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Abstract

The feasibility of inspecting under-lagging steel pipes without lagging removal using the magnetostrictive depth gauge is described. With the MDG, elastic waves are launched along the length of a pipe, and reflected echoes from defects such as cracks or corroded areas are detected using noncontacting sensors. Experimental results obtained from 6-m long, 3.8-cm diameter steel pipe samples before and after inducing simulated defects in the pipewall are presented, and the potential capabilities of the MsS technique are discussed. In this paper, after an introduction to the basics of magnetostriction and magnetostrictive materials, some of their uses and applications are presented. New position sensors based on the magnetostriction effect and the magnetostrictive delay-line technique are presented with respect to their applicability in engineering systems. It is also shown that the magnetostriction effect can be used in measuring the M(H) and l(H) functions as well as their uniformity response. Finally, the so-called magnetoelectric effect is discussed as one of the major future trends of magnetostriction and magnetostrictive materials for sensing applications.

1.0Introduction

Magnetostrictive depth gauges are used worldwide in a variety of different applications, ranging from robotic arm movement sensors on car a production line, to the measure of a liquid level in an industrial plant vessel. This report focuses on the device used in liquid level measurement applications.

Today's process plants have a higher than ever demand for precise and reliable measurement systems in order to maintain a high product quality. Just one of the many critical systems required for high product quality is level measurement. By improving level measurement technology, it is possible to reduce chemical-process variability, which in turn will result in higher product quality. This will also contribute to lowering one of the major factors of any plant - cost.

Liquid level can be determined using a variety of different methods, ranging from the simple sight glass, to the differential pressure transmitter. Choosing a level sensor depends on many factors, including the process conditions, cost, accuracy required, reliability, etc. The Magnetostrictive level sensor operates in such a way that it requires little to no maintenance, incorporates high reliability, high repeatability, and very high accuracy. This device is therefore the chosen option in many critical process applications.

Objectives

The aim of this report is to demonstrate the working principles of a fully operational Magnetostrictive Level Sensor. In order to achieve this, the following tasks must be carried out;

Research

In order for the design of the project to commence, the following points must be looked at;

Theory of operation - this will include how the instrument actually works, and all principles and effects behind the operation, e.g. Wiedemann effect.

Application - this will include the types of applications this instrument is best suited for, and why it could be the preferred choice over similar level measurement devices.

Construction of instrument - this part of the research is necessary in order to build the device. It will include materials of parts, e.g. the float, stem, housing of sensor, wire, permanent magnet, ...