Precision Sine Wave Signal Source Design

Linear displacement transducer (LVDT) is linear displacement transducer, as the name implies, it is used to measure the elongation and the expansion of objects and so on. Sine wave signal source provides the reference signal of the excitation for the linear displacement sensor to guarantee its reliability, stability. Since the output of the common source of current and power are low, which can not automatically close loop according to changes in load, it can not determine the amplitude and frequency of the output of the sine wave signal, limiting the field of application of the LVDT. The topic has designed to fit the open-loop and closed loop curve intelligently, which acts CAN bus and USB bus as the communication interface. The dual-channel high-precision sine wave signal source:the range of the valid values of the output signal is1Vrms-40Vrms, and the range of the frequency is50Hz-4000Hz, and the maximum of the load current is2A.The main work of this paper is:(1) The use of DDS technology, low-power, programmable waveform generator AD9833is designed to generate sine fundamental, combined with12D/A Device AD5445Amplitude adjustment, and then amplified by the power amplifier and the output of the circuit.(2) Since the system has a linear characteristic, by the principle of the least squares curve fitting, the device in programmed mode can intelligently fit the open loop curve and the closed loop curve. PID closed-loop adjustment process outlines as follows:After the master Cortex-M4receives the values of frequency and voltage, the master Cortex-M4produces output by the fitted open-loop curve.The system compares the value of feedback with the value of closed-loop reference, by the offset value to adjust the magnification of the current fundamental sinusoidal.(3) In order to improve the accuracy of the value of the voltage feedback loop, the IIR digital filter is designed, which can complete the FFT spectrum analysis to the value of the feedback, to reduce the drift of the circuit, electromagnetic interference, the fluctuations of tle load and so on affecting the output of voltage and frequency of sine wave signal.(4) I select the STM32F407ZGT6S, the latest processor of STMicroelectronics, as the master chips of the system, achieve to manually set panel, finish remote human-computer interaction, generate the fundamental sine, and apply the closed loop PID algorithm and the filtering algorithm.(5) The subject is designed AC to DC rectifier modules, rectifying AC power supply220V/50Hz to DC power required for the system, making the system portable and low cost.(6) The subject selected CAN, USB communication interface, increasing the rapidity adnd security of data transmission. The platform of the software code of the topic is IAR Embedded Workbench for ARM6.40, and the version of the firmware library is V1.0.0, and the programming language is C.