A high precision driver for an eddy current displacement sensor
Niemann, Hester Elna
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This dissertation presents the design and development of a high precision driver for an eddy current displacement sensor. The project was initiated to supplement the development of a low-cost PCB eddy current displacement sensor for active magnetic bearings (AMBs). The sensor driver will be implemented in AMB systems that will be used in various high-speed applications. The sensor driver is required to drive an eddy current PCB sensor, condition the output signals from the sensor, and send the conditioned position signals to an embedded digital controller. Circuit board design and development therefore constitute the main focus of this project. Research on the defining concepts of the project was imperative in gaining the necessary understanding of the project. AMB systems and the sensors used in these systems were investigated first. The eddycurrent type sensor used in this project, as well as the PCB sensor technology used were also researched. As analogue design constituted a main aspect of this project, the concepts of signal conditioning and sensor characteristics had to be comprehended. The sensor driver consists of several sub-systems, including a sensor excitation circuit to drive the sensor, a signal conditioning circuit to condition the output signals of the sensor, and a digital processing circuit for further processing of the position signals. A conceptual design was performed for each of these sub-systems, followed by a detail design, in which the conceptual designs of the sub-systems were realized. All the sub-systems were then integrated, and lastly evaluated. The evaluation of the sensor driver system included verification and validation of the system. The sensor driver design was verified, while the final sensor driver board was validated with regards to its specifications. Additional circuit characteristics such as signal-to-noise-ratio, sensitivity and resolution were also determined in order to characterize the sensor driver system. The overall outcome of the sensor driver project was successful, with all the characteristics of the sensor adhering to the requirements. It was determined that the sensor driver has a signal to noise ratio of 54 dB, a linearity of 9 %, a sensitivity of 26 .4 V/mm, and a resolution of 792.5 nm. Recommendations are made with regards to the sensor cables, heat distribution, and the low-pass filter on the field programmable gate array (FPGA). Future work will mainly focus on implementation of the sensor driver on a test bench and implementation of the linearization algorithm. Additional future work includes a study on EMC effects on the system and especially the cables, and further firmware enhancements of the sensor driver. These include input signal testing and temperature compensation. An investigation on the required excitation current for optimal sensor operation should also be done.
- ETD@PUK