This article develops a new inductive displacement sensor with a segmented multi-group coil structure, which is suitable for the displacement measurement of control rods in nuclear reactors. Each group coil of the sensor consists of two excitation coils and one sensing coil. The excitation and sensing coils are segmented to extend the linearity range of the displacement sensor. It abandons the traditional sensor’s method of using nonlinear compensation to achieve large-stroke displacement measurement. Providing an alternating current (AC) signal to the excitation coil and processing the induced voltage generated by each sensing coil can directly achieve the high-precision measurement of core displacement. The mathematical model of the variations in the sensing coil voltage caused by the movement of the core is established. The impacts of the excitation coil structure, the number of turns of the excitation coil, and the excitation frequency on the output characteristics of the designed sensor are analyzed by finite element simulation. Based on the analysis and design, a sensor prototype is built and tested in the laboratory. The measurement results show that the linearity error is 0.35% and the maximum measuring error can be limited within 1.5 mm, which is sufficient to meet the practical requirements in a nuclear reactor environment.

Inductive position sensors have been widely employed in nuclear reactors for monitoring the control rod position. Accurate control rod position information plays a crucial role in regulating the power of nuclear reactors. However, the inductive sensors currently used for control rod position detection exhibit limited measurement accuracy, which may adversely affect safety and reliability. In response to these issues, a segmented coil structure inductive position sensor based on the resonance principle is proposed in this paper. To improve the sensor sensitivity, a resonant circuit is implemented by connecting capacitors in series with the excitation and sensing coils, and a theoretical model is developed. Furthermore, optimizing the resonant capacitance can reduce the nonlinearity error of the sensor. To enhance the load-driving capability of the excitation source, a single-phase inverter circuit is proposed as the excitation source. Only one excitation signal is used to excite multiple coils. ANSYS simulations and experimental measurements are performed to compare sensors with and without the resonant circuit. The results validate the theoretical analysis and demonstrate that the sensor employing the resonant circuit significantly improves sensitivity and enhances linearity range. The sensor achieves a sensitivity of 0.1909 V/mm and a nonlinearity error of less than 2% over the full-scale span.