Design And Research Of Data Acquisition System Of Current Meter

Data acquisition system is an important part of current meter calibration system, one of the key factors to complete this design is whether the frequency of current meter can be measured accurately. The key point of data acquisition is, in factors of hardware, some measures can be used to reduce or even eliminate all kinds of interference; in factors of algorithm, calculation method with different counting time can be used to flite and count various input waveforms.Based on the extensive understanding of national standard, design of domestic and foreign current meter calibration system, this system is designed from the hardware and algorithm factors. First of all, according to design requirements, completed domestic and foreign projects and the design scheme, an embedded system based on MCU is designed and the hardware is selected including the microprocessor, communication interface and signal condition circuits. Secondly, to improve accuracy of data acquisition, the difficulty of signal acquisition is analysed and signal condition circuit is designed to eliminate the interference from water resistance, spike signal, chatter signal. The error analysis, comparison between the frequency measuring method and cycle measuring method, and software filtering method for different speed has been selected. The least square method is used to process data. At the same time, the C language program of the data acquisition and ASCⅡ communication protocol between current meter and PLC are designed and writed. Considering the input supply voltage amplitude of some current meter has special requirements, a DC-DC circuit based on PWM signal output by the microcontroller is designed, especially focusing on the design and calculation of parameters of this circuit.In the simulation, the signal condition circuit in the third chapter is simulated to verify its validity. The frequency measuring method and cycle measuring method is simulated to verify its applicability and validity. The least square method is simulated to verify the rationality of second-order algorithm for this system. The ASCII communication protocol is tested to verify its feasibility. The numerical control DC power is simulated to verify its rationality of this design and feasibility.Compare with the Liaoning current meter calibration system before, this data acquisition system can collect more velocity models accurately, and there are more abundant method in the treatment of voltage waveform signal, the fluency and rationality of communication system has been strengthened.