12:00 PM - 12:15 PM
[PCG20-12] Investigation and development of FPGA coding for digital-type fluxgate magnetometer
Keywords:magnetometer, small satellite, space observation, planetary exploration
For the digital-type fluxgate magnetometer, developed for use on spacecraft, a Field Programmable Gate Array (FPGA), a digital logical processor, is used for the most of the pickup signal from the sensor. Therefore, the weight and power consumption of its circuit can be reduced compared to analog-type fluxgate magnetometer. Recently the target of space exploration is expanded to the wider area in the solar system. As a result, observation instruments of wider variety are installed on a single spacecraft and the technology for the in-situ observation has been developed to suit that condition. Digital-type fluxgate magnetometer, which is small and power-saving compared with the conventional analog-type, is more suitable for the future exploration by spacecraft, on which more various and smaller observation instruments would be installed. Meanwhile the devices and materials used in instruments on spacecraft require a high degree of reliability and must be tolerant of the severe space environment, e.g., high and low temperatures and radiation. The reliability and environment tolerance strictly restrict the available device, material and design of the instruments. The goal of this research is to develop a digital-type magnetometer with improved performance over conventional one while overcoming these limitations.
This study and development are based on the design of a digital-type fluxgate magnetometer developed for the SS-520-3 sounding rocket experiment. Since the output data from the magnetometer to the magnetic-field input depend on the frequency of the magnetic field time variation, the frequency characteristics of the response of the magnetometer should be evaluated with high accuracy. We numerically simulated and modeled the frequency characteristics and derived the overall transfer function of the digital-type fluxgate magnetometer. When the frequency response of the model was compared with the actual one of a test device designed similarly to the digital-type fluxgate magnetometer installed on the SS-520-3 sounding rocket, differences were identified. These differences are supposed to be caused by the modulation process of the signal. The fluxgate magnetometer includes a sensor unit that detects external DC magnetic fields and modulates them into AC pickup voltages, as well as a phase detection unit that demodulates the AC pickup voltages into DC signals corresponding to their amplitude. In the numerical model, the conversion coefficient for AC modulation in the sensor unit is assumed to be constant, independent of the frequency of the external magnetic field. On the other hand, the phase detection unit's computations, performed in the FPGA, may not be exactly simulated by the model due to the shortage of accuracy in the mathematical expression of the frequency characteristics of the modulation operations. To improve the model, we are measuring the actual transfer function of the sensor unit's AC modulation and incorporating it into the model. Additionally, the FPGA computation process is being revised to allow for monitoring of intermediate signals, enabling a more detailed comparison between the model and the actual device. These efforts aim to achieve better agreement between the frequency characteristics of the model and the actual hardware.
In this presentation, we will provide a detailed analysis of the frequency characteristics of the signal modulation process, present an updated frequency response model incorporating these findings, and discuss the suitable scheme to define the FPGA parameter design to enhance the performance of digital-type fluxgate magnetometers.
This study and development are based on the design of a digital-type fluxgate magnetometer developed for the SS-520-3 sounding rocket experiment. Since the output data from the magnetometer to the magnetic-field input depend on the frequency of the magnetic field time variation, the frequency characteristics of the response of the magnetometer should be evaluated with high accuracy. We numerically simulated and modeled the frequency characteristics and derived the overall transfer function of the digital-type fluxgate magnetometer. When the frequency response of the model was compared with the actual one of a test device designed similarly to the digital-type fluxgate magnetometer installed on the SS-520-3 sounding rocket, differences were identified. These differences are supposed to be caused by the modulation process of the signal. The fluxgate magnetometer includes a sensor unit that detects external DC magnetic fields and modulates them into AC pickup voltages, as well as a phase detection unit that demodulates the AC pickup voltages into DC signals corresponding to their amplitude. In the numerical model, the conversion coefficient for AC modulation in the sensor unit is assumed to be constant, independent of the frequency of the external magnetic field. On the other hand, the phase detection unit's computations, performed in the FPGA, may not be exactly simulated by the model due to the shortage of accuracy in the mathematical expression of the frequency characteristics of the modulation operations. To improve the model, we are measuring the actual transfer function of the sensor unit's AC modulation and incorporating it into the model. Additionally, the FPGA computation process is being revised to allow for monitoring of intermediate signals, enabling a more detailed comparison between the model and the actual device. These efforts aim to achieve better agreement between the frequency characteristics of the model and the actual hardware.
In this presentation, we will provide a detailed analysis of the frequency characteristics of the signal modulation process, present an updated frequency response model incorporating these findings, and discuss the suitable scheme to define the FPGA parameter design to enhance the performance of digital-type fluxgate magnetometers.