1 introduction with the development of technology, embedded operating system in more and more important role to play in the field, the level of product technology has become one of the signs. one linux because of its open, multi-user, multi-task, good user interface, rich network functionality, reliability and system security features such as good portable widely applied to the instrument measuring devices. conventional measuring equipment (with tesla meter, gauss meter) widespread low accuracy (typical accuracy 1.5%), easy to maneuver and other shortcomings. this paper presents an embedded linux-based frequency measurement system, which not only meet the current needs of the data capture, but also because of its embedded operating system linux, so has the reliability, scalability features, not only enhance the measurement accuracy, but also function as instruments to bring convenience to upgrade. can be used in laboratory instruments, medical instruments, attitude control , safety testing and other areas required to detect the . 2 hardware structure of the measurement system measurement system using arm9 hardware structure as the controller, and signal amplification, rectification filtering, amplification and other programmable hardware configuration of the entire measurement system. moreover, the measurement system also with a usb, rs232, ethernet communicate interface, system communication capability, enabling the network networking capabilities. the hardware structure as shown in figure 1. arm9 embedded processor using samsung's $ 3c2410. s3c2410 is based on the arm920t core 16/32-bit embedded risc microprocessor targeted at handheld devices and high-cost, low power applications. it uses five lines and full performance of the mmu, while the chip integrates the functions of expansion of large units, such as l cd controller, i2c bus, touch screen interface, usb interface. powerful chip simplifies system design, not only reduce the system vol ume, and improve system reliability. usb, rs232 and ethernet interfaces for different communications systems, suitable for different environments and conditions of measurement, ethernet interface, the system can achieve networking. in the measurement system, you can easily use the touch screen to control the system to achieve different display mode switching, parameter setting and measurement data storage and other functions. voltage signal part of the measurements, obtained by the weak sensor voltage signal by the amplified input rectifier control system and other measures. alarm output can achieve user-set upper and lower alarm limits, user-friendly measurement site monitoring. 3 magnetic measurement system for front-end signal processing module measurement system sensors for the measurement method using electromagnetic induction method. method is to measure electromagnetic induction coil placed in an alternating , according to faraday's law of electromagnetic induction be tween the coils of wire will be induced electromotive force and the size of the induced emf across the coil is proportional to the size of magnetic flux. induced electromotive force e is: measurement system front-end signal processing module structure shown in figure 2. (1) in order to achieve multiple sensor signal input, the design used in the channel chip select chip 74hcl5 choice. by 74hcl53 control terminal s0, sl input different data sets (00,1 o, 0l, 11), ly and 2y output can be achieved on the choice of different input channels. (2) in the whole system of circuit design, the preamplifier's main role is the sensor output, and the magnetic field strength is proportional to the weak voltage signal amplification. according to its requirements, design of preamplifier circuit using differential amplification means, the circuit shown in figure 3. it has a high cmrr, high input impedance, low output impedance, offset a small, drift is small, and good linearity.
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