Development and prototyping of a Point Coupled Linear Transformer (PCLT) displacement sensor

The main aims of this project were to develop and prototype a Point Coupled Linear Transformer (PCLT) displacement sensor, and to perform a general exploration of the PCLT technology. The PCLT is a recent invention that has planar PCB windings and a non-contacting movable core, and relies on variable induction to detect displacement. Different core materials and shapes are investigated. The transformer windings layout is optimized for symmetrical response and high primary to secondary voltage coupling. Frequency is identified as a critical factor in PCL T performance. Investigation is done into the resonant properties of the PCL T, and series and parallel capacitors are used to control the resonant frequency and alter the shape of the coupling peaks that occur at said resonance. Advantages and disadvantages of operating the PCL T at resonance are identified. The groundwork is laid for further investigation into this aspect of the PCLT. The magnetic field strength around the sensor is tested, and 3D graphs are presented. Various prototypes of a I-Dimensional PCL T are developed that utilize different methods of signal conditioning to extract core position from the detected secondary signals. The prototypes' performance is tested and comparisons are made. The prototypes using synchronous demodulation outperform the ones using passive demodulation. A ratio-metric calculation carried out on the detected signals is found to improve sensor linearity. Results from the best ID prototype are: );> Linearity of 1 % FS (64mm stroke) and 0.18% FS (32mm stroke) );> Output noise of2 mV (peak-peak) and drift ofO.5mV over 12 hours );> Resolution of at least 8.3Jlm or 0.013% FS );> Repeatability of 3 .2Jlm or 0.005% FS 111 Un ive rsi ty of Ca e T ow n Recommendations are made to: increase the stroke-to-Iength ratio (currently at 68% max), increase the operating frequency (currently at 20 KHz), and use synchronous demodulation in conjunction with a ratiometric calculation, in future versions of the peLT. Methods and circuits developed for the 1 D peLT are used to create a 2-Dimensional peL T. This sensor shows poor results, due to a lack of magnetic flux in the central region of the sensing area. Recommendations are made to redesign the primary coil with a spiral one such that a constant magnetic field is generated over the entire sensing area. Passive demodulation (which is phase insensitive) is found to be better suited to 2D peLT signal conditioning due to the large phase changes that occur between the secondary signals as the core position changes. IV Un ive rsi ty of Ca pe To wn Table of