外文翻譯--基于虛擬儀器技術(shù)的風機性能自動測試系統(tǒng)-在線瀏覽
2024-09-04 20:13本頁面
【正文】 DAQ board input signal type and range, 0 ~ 5 V voltage signals are achieved from 4~20 mA current signals by an interface board which is used for signal transformation.Through the analog output channel on 6024E, 0~5 V voltage signal which is corresponding on 0~50 Hz of AC frequency, are sent out to control frequency converter ( type, MITSUDISHI, Japan). Then, the fan speed changes with variable voltage.The regulating unit of working status, which is designed by the authors, is the rotating baffle structure posed of round baffle, shaft coupling, creeper gear and step motor etc. (See the ). This kind of structure can not only realize the auto control but also is small and flexible. Three digital I/O port on the 6024E are used to send out three phase pulse to control the rotation angle of step motor. The step motor drives the round baffle through the creeper gear to revolve inside the wind pipe, resulting in the change of aperture gap between the round baffle and windpipe, thereby altering the flux of airflow inside the windpipe, namely the alteration of working status is realized. The creeper gear can prevent the position of round baffle changing when the airflow is too strong.To insure the measurement accuracy, several antiinterference means are adopted such as differential inputs of signals to eliminate the mon mode interference, good earth of signal line and instruments, digital filtering technology in software[7].3 Software design of the system Data processingData processing in this system includes three aspects: processing acquired signals to weed out various disturbing signals。 fitting performance parameters based on least square method to draw performance curves of fans. Calculation of performance parameters Refer to the national standard GB123685[8], Aerodynamics performance test procedure of ventilator, the ventilator performance testing of the discharge outlet is achieved. The fan performance parameters are calculated as follow so:where dnis the aperture of restriction orifice。εis the gas expansion coefficient。Fis the torque between motor and fan。Pstis the static pressure。Ais the area of wind pipe。ηis the available output. Performance curve fitting There are many curve fitting methods such as exponential fitting, orthogonal polynomial fitting and Chebyshev fitting. The least square method is adopted to fit performance parameters because the characteristic curve of fan is mostly parabola. What is called least square method is statistically processing the observed values from experiments to make desired value of observation equal to its theoretical value and rectify the observed value[9]. Using the functionPolyFitthat is in the advanced analysis library of LabWindows/CVI, the performance curve fitting was pleted. The format of function PolyFit is as follows: PolyFit(double x[],double y[],int n,int order, double z[],double coef[],double*mse)The purpose of this function is to find the coefficients that best represent the polynomial fit of the data points (x,y) using the least squares method. PolyFitobtains theithelement of the output array and mean squared error ( mse ) using the following formulae[7]: where xis flux。zis best fitted value ofy。nis number of sample points。waveform display of signals, are delivered in the
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