外文翻译--基于labview的虚拟示波器研究和开发

外文翻译--基于labview的虚拟示波器研究和开发内容摘要：

veform, change the coordinate of the zero mark at the same time. So the zero mark will move with the waveform. In addition, set the mark button control invisible outside the top and bottom edges, that the effect can be truer. As seen in . E. Other functions What discussed above are the 3 basic functions in a virtual oscillograph. For other functions such as trig mode, couple mode, cursor, data storage, replay and print etc. are not discussed in this paper. According to actual needs, all the functions mentioned above can be achieved well through making full use of the property node in LabVIEW. III. CALCULATION OF FREQUENCY AND PERIOD Period and frequency are key parameters to a periodic signal. Traditional measurement is to count the standard signal during the gate pulse duration in hardware so as to calculate the period of the measured signal. But there areusually no counters on hardware to use for a virtual oscillograph based on PC. It must be measured through software. However, the significance in a virtual oscillograph is that it can conveniently analyze the data collected by board cards, and then get the waveform39。 s eigenvalue. So the basic clew to measure the waveform39。 s period is to find the time slot between the Kth period and the (K+1)th period from the collected waveform data. Base on this thought, we introduce one method called gate voltage measuring to measure the signal period. [8] The period of a periodic signal can be defined as the time slot that the signal across a specified gate voltage from the same direction (positive or negative edge) two times. As seen in Fig. 6 附 录 6 Suppose a signal sample Xi, (i N), N is integer, the total number of the sample data. Take the average value of the sample data as the gate voltage。 pare it with Xi one by one. When Xi=v and Xi1v, the waveform is across the gate voltage from the bottom up, called positive edge。 when Xi=v and Xi1v, the waveform is across the gate voltage from the top down, called negative edge. At the same time, to eliminate the infection brought by interference, get ride of the positive and negative edges whose interval is less than 10 sample points. So the position of positive and negative edge is acquired. Because the sampling rate is unchangeable, so the time slot between two sampling data is fixed. Thus the signal frequency and period can be calculated. [9] Suppose the sampling rate is f0 , the period is T0, T0 = 1/ f0, sampling rate39。 s error coefficient is a. The measured signal39。 s frequency is f, period is T, T= 1/f。 the frequency measured actually is fC, TC, TC= 1/fC. Suppose at every sample time the sample contains k full periods of the measured signal, and the exact time is kT . The time of the first edge cross the gate point phase is t. Because of the disperse sample, at the kth period, the time when signal passes across the gate point phase t+kT may have an error 177。 △ T0. Considering the sampling rate error, at the worst state, at the kth period, the time when signal passes across the gate point phase is t+kT+(αkT177。 △ T0 )， and the time the k signal periods pass is t+kT+(αkT177。 △ T0) .So there it is: Suppose the sample length is L, there is L△To≈kT. Put it on the Eq. (2) above, there is: When a is far smaller than 1/L， increasing the L value can increase the measure precision consumedly. When a is as much as 1/L, there is no significance to increase the L value. a is fixed on system39。 s hardware. With a, it can find the proper L value that make the sample and calculation process under the best precision. Suppose the square signal, its pulse duration is T39。 , the one measured is TC39。 , so there is: 附 录 7 What discussed above is the period and frequency measurement in the sampling procedure, putting forward the measurement precision theory. But to the amplitude, rise time or spectrum analyze etc. are not discussed in this paper. Using the data group collected, the user can develop other better measurements. In LabVIEW, there is plenty of measuring VIs, which can measure the parameter exactly. [10] Combining the control procedure with virtual oscillograph can achieve better effect. Next, take DC motor39。 s PWM speed control for instance, it will introduce the function that using virtual oscillograph in PID and closed loop feedback controlling. IV. APPLICATION IN MOTOR SPEED CONTROL Lockphase technology plays an important role on motor speed control. With the technology, it can improve the precision of motor speed。 and also, it does stepless speed variation control only by changing the specified frequency, that will be conveniently used on controlling more than one motor work synchronously. [11] The basic theory diagram that indicates the speed control system based on PPL closedloop lockphase is shown in . Suppose the specified pulse met the motor speed is fR, the pulse from photo sensor is fF. Compare their frequency and phase in the phase parator, and bring the signal voltage proportion to frequency and phase difference. This voltage controls the motor speed through the lowpass filter to synchronize the motor speed and the specified control signal. In case the load is fluctuating which changed the motor speed, the pulse output from photo sensor is changing at the same time. There is difference between it and the specified signal. So the output of the phase parator through the lowpass filter and driver circuit is changing, and make the motor faster or slower until the two frequencies of feedback and specified bee equal. At that time, the motor is steady again. The feedback frequency is locked to the specify frequency, so the system control precision is very high. Combining the phase parator and puter, taking the advantage of measurement and control of virtual instruments, we can get the digital lockphase closed loop circuit. The theory diagr。