Measuring Surface Displacement of Water

Table of Contents

Introduction
attocube’s Interferometric Sensor
Experimental and Results
Conclusion

Introduction

Measuring vibrations with amplitudes of a few picometers, as well as displacements with nanometer accuracy, on a wide range of materials is a very challenging task as it is not possible with most of the commercially available measurement techniques.

attocube’s Interferometric Sensor

This article presents measurement results on a liquid surface obtained by matching the sensor head of attocube’s Industrial Displacement Sensor (IDS) to the material and application. A unique feature of the IDS is that it can accommodate advanced applications, for instance under extreme environmental conditions and in very constrained spaces. The sensor heads developed by attocube have a diameter below 1 mm and are suitable for temperatures up to 400 °C. This article discusses the results of displacement measurements performed on a water surface in order to demonstrate the flexibility of attocube’s interferometer system.

With attocube’s IDS3010 interferometric sensor, displacement measurements down to the picometer range can be performed. The broad sensor head portfolio has been designed to perform measurements on different surfaces and materials such as gold, silver, aluminum, steel, copper, silicon, ceramics, plastics, glass, or even water. Angular tolerances and working distances rely on the surface reflectivity as well as the type of sensor head employed. Using a standard target, such as a retroreflector, the possible working distance is immediately after the sensor head and can go beyond a range of 30 meters.

The ability to measure liquid surface movements paves the way to realize innovative applications in a variety of industrial and scientific areas, for instance, determining the liquid level in falling film reactors, vibration measurements and analyzes of hydraulic systems, and detecting liquid levels in a hydrostatic leveling system [1].

Experimental and Results

The schematic setup for displacement measurements performed on a water surface is illustrated in Figure 1. The experimental setup consisted of two focused sensor heads with a focal length of 40 mm (F 40 mm) secured on an optical table, an aluminum mirror, and a cup of water. The focus was on the water surface and a working range of a few millimeters with angular tolerances of a few tenths of degrees was achieved.

experimental setup

Figure 1. The figure shows a sketch of the experimental setup to perform simultaneous displacement measurements on the surface of water and on a mirror.

Figure 2 shows a plot depicting the displacement measurement results. As can be seen in Figure 2, during the first 0.714 seconds, the water surface (blue curve) is only slightly wavering with 11.6 Hz when compared to the stable position measurement of the mirror (red curve). When the optical table is hit between the two targets using a hammer, the water surface oscillates with a maximum deflection of approximately ± 20 µm. The zoom reveals that for the first milliseconds following the excitation, the two measurement arms exhibit similar behaviors in the high frequency range.

displacement measurement results

Figure 2. The blue curve shows the water surface and sensor head movements and the red curve represents the displacements measured on the side of the mirror after hitting the optical table with a hammer.

Conclusion

From the results of this experiment, it is evident that the interferometer sensor is capable of tracking water surface movements.

Reference

[1] Meier E, Limpach P, Geiger, Ingensand H, Steiger A, Licht H and Zwyssig R 2010 Journal of Applied Geodesy 4 2 91-102

This information has been sourced, reviewed and adapted from materials provided by Attocube Systems AG.

For more information on this source, please visit Attocube Systems AG.

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