Design and Development of a Planar Linear Variable Differential Transformer for Displacement Sensing

In this paper, we present a new, efficient displacement sensor using core-less planar coils that are magnetically coupled. The sensor consists of two planar stationary coils and one moving coil. The mutual inductance between the stationary coils and the moving coils are measured, and the displacement is computed. The sensor design was validated using numerical computation. Two prototype sensors of different dimensions were fabricated and tested. The first prototype sensor developed has a measurement range of 70 mm and an R.M.S. error of 0.8% and the second sensor has a measurement range of 56 mm and an R.M.S. error in measurement of 0.9%. The signal output from the sensor is made tolerant to errors due to variations in the vertical position of the moving coil. The new sensor is low in cost, easy to manufacture, and can be used in a number of industrial displacement sensing applications.