Journal of Optoelectronics and Advanced Materials Vol. 4, No. 2, June 2002, p. 347 - 352 POSITION SENSORS BASED ON THE DELAY LINE PRINCIPLE P. Kemidis, C. Orfanidou, E. Hristoforou Laboratory of Physical Metallurgy, Department of Mining and Metallurgical Engineering, National Technical University of Athens, Athens 15780, Greece In this paper, we present a position sensor based on the magnetostrictive delay line principle. The sensor is accompanied by its electronic circuitry and packaging. We analyze the sensor working principle, electronics, calibration procedure as well as its evaluation with respect to the state of the art, showing its advantages and applications. (Received February 27, 2002; accepted May 15, 2002) Keywords: Magnetostrictive delay lines, Position sensors 1. Introduction The primary standards in measuring length are governed by the definition of the meter, which is the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The experimental realization of this definition with respect to the uncertainties of the modern atomic clocks and the sharp Gaussian frequency response of lasers, offer an uncertainty of measurement of the order of parts per billion (ppb). The secondary methods in measuring position are mainly referring to interferometric techniques, with corresponding uncertainty of the order of 1 part per million (ppm). The laser interferometers are currently used not only as secondary standards but also as sensing elements in given applications. Nevertheless, in cases where the use of interferometers is not appropriate, other kinds of position sensors are used. Many physical effects have been employed in the past to develop such position sensors, based on the electrical, magnetic and optical properties of materials. In our days, these sensors should be contactless devices with built-in electronic circuitry including electronic auto-calibration algorithms, with sensitivities and uncertainties better than 1 m and 10 m/m, respectively. In some cases, where the environmental conditions do not allow the use of optic or capacitive techniques, magnetic phenomena and techniques are the only solution for more trustful measurements. Modern magnetic materials have enhanced the properties of sensors based on magnetic effects and have also initiated new sensing elements and applications, so that magnetic materials are competitive with respect to other sensing principles[1-4]. There is a wide variety of industrial applications requiring position measurement where the position sensor should have cross section area smaller than 2 mm x 5 mm, uncertainty of measurement better than 0.1 mm per meter and a speed of sensing head displacement faster than 10 m/s. Most importantly it should be able to perform measurement in mechanically harsh environments [5-12]. We used the magnetostrictive delay line (MDL) technique [13] by using some new materials, which enhance the properties of this technique, in order to develop a position sensor that should meet the above mentioned specifications. The specific application we have had in mind was the realization of a position sensor able to detect the position, speed and acceleration of a hydraulic piston. This sensor is to be presented hereinafter.