单片机外文翻译外文文献英文文献单片机的超声波测距系统的研究与设计.pdf

附 录 附录 A 外文翻译 the equivalent dc value. In the analysis of electronic circuits to be considered in a later course, both dc and ac sources of voltage will be applied to the same network. It will then be necessary to know or determine the dc (or average value) and ac components of the voltage or current in various parts of the system. EXAMPLE 13.13 Determine the average value of the waveforms of Fig. 13.37. FIG . 13.37 Example 13.13. Solutions: a. By inspection, the area above the axis equals the area below over one cycle, resulting in an average value of zero volts. b. Using Eq.(13.26): as shown in Fig. 13.38. 26 In reality, the waveform of Fig. 13.37(b) is simply the square wave of Fig. 13.37(a) with a dc shift of 4 V; that is v2 = v1 + 4 V EXAMPLE 13.14 Find the average values of the following waveforms over one full cycle: a. Fig. 13.39. b. Fig. 13.40. 27 Solutions: We found the areas under the curves in the preceding example by using a simple geometric formula. If we should encounter a sine wave or any other unusual shape, however, we must find the area by some other means. We can obtain a good approximation of the area by attempting to reproduce the original wave shape using a number of small rectangles or other familiar shapes, the area of which we already know through simple geometric formulas. For example, the area of the positive (or negative) pulse of a sine wave is 2Am. Approximating this waveform by two triangles (Fig. 13.43), we obtain(using area 1/2 base height for the area of a triangle) a rough idea of the actual area: A closer approximation might be a rectangle with two similar triangles(Fig. 13.44): 28 wh