基于FPGA和磁传感器阵列的磁场扫描系统

Magnetic field scanning system based on FPGA and magnetic sensor array

为实现铁磁性物体的无损检测,设计了一种基于FPGA和磁传感器阵列的磁场扫描系统。本系统采用了FPGA作为主控器,其中包含了AD配置模块、AD接口模块和数据缓存模块,FPGA控制传动装置进行扫描,通过磁传感器阵列扫描将磁场转换为对应的电压信号,通过以AD7768为核心的模数转换模块将电压信号传送给FPGA,实现8路并行高速磁场数据采集,然后在FPGA中通过双线性插值和伪彩色转换算法的处理,把采集的磁场数据转换成磁场分布的图像,存储在SD卡中并在LCD中实时显示。实验中,使用磁场扫描系统对环型磁铁、磁化后的铁丝、内嵌于木板中的铁钉、剥线钳和尖嘴钳进行了磁场扫描,采用基于磁通量与大津法为基础的程序处理,对物体进行定位与识别,定位的均方根误差平均值为3 mm,测量的长度接近实际物体的长度,能够辨别磁性物体的位置和方向,能够通过物体的特征磁场识别磁性物体,达到对铁磁性目标的无损检测和识别的目的。本系统采用了以FPGA ZYNQ7010、AD7768、HMC1001为主的电路采集磁场数据,具有采集速率高、扩展方便、功耗低,能获取磁场空间分布图像等优点,可以应用于铁磁性目标的定位和识别等领域,如安全检测、地下水下的磁性目标探测等。

In order to realize nondestructive testing of ferromagnetic objects, a magnetic field scanning system based on FPGA and magnetic sensor array is designed. FPGA is the main controller of this system that includes AD configuration module, AD interface module and data cache module. FPGA controls the transmission device to scan, and the magnetic field is converted to the corresponding voltage signal by the magnetic sensor array and the circuits. The voltage signal is transmitted to FPGA through the analog-to-digital conversion module with the core of AD7768, and high-speed magnetic field data acquisition system with eight parallel channels is realized. Then, through bilinear interpolation and pseudo-color conversion algorithm in FPGA, the collected magnetic field data are converted to the image of magnetic field distribution, which is stored in SD card and displayed in LCD in real time. In the experiment, the magnetic field scanning system is used to carry out magnetic field scanning for the ring magnet, magnetized wire, iron nails embedded in the wood plate, wire stripping pliers and needle-nose pliers. The program, based on magnetic flux and OTSU method, is used to locate and identify the object. The average root mean square error of positioning is 3 mm, and the measured length is close to the length of the actual object. The position and direction of the magnetic object could be identified, and the magnetic object could be identified by the characteristic magnetic field of the object, so as to achieve the purpose of nondestructive detection and identification of ferromagnetic objects. FPGA ZYNQ7010, AD7768, HMC1001 are used to collect magnetic field data in the system. It has the advantages of high acquisition rate, convenient expansion, low power consumption, and can obtain magnetic field image with spatial distribution. It can be applied to the location and recognition of ferromagnetic targets, such as safety detection, magnetic target detection of underground and underwater.