电子信息类专业英语,http:/www.cmpbook.com,机械工业出版社同名教材配套电子教案,温丹丽 高源 制作,Passage One Multimeter and Oscilloscope,1What are the functions of the two screws on the multimeters? 2What can an oscilloscope measure? 3How can you determine the frequency of a waveform?,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,Words and Expressions case keis n. 案例 decibel 5desibel n. 分贝 needle 5ni:dl n. 针 jack dVAk n. 插孔 ohm Eum n. 物欧姆 screw skru: n. 螺旋，螺杆,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,waveform 5weivfC:m n. 波形 centimeter (cm) 5sentImi:tEr(r) n. 厘米 horizontal 7hCri5zCntl ad. 地平地，水平地 superimpose 5sju:pErim5pEuz v. 添加 oscilloscope C5silEskEup n. 物示波器 multimeter n. 物万用表 DC voltage 直流电压 AC voltage 交流电压 DC current 直流电流 AC current 交流电流 cathode-ray tube (CRT) 阴极射线管,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,Text 1. Multimeter A multimeter (shown in Fig.3-1) is a general-purpose meter capable of measuring DC and AC voltage, current, resistance and in some cases, decibels. There are two types of meters: analog, using a standard meter movement with a needle, and digital, with an electronic numerical display. Both types of meters have a positive (+) jack and a common jack (-) for the test leads, a function switch to select DC voltage, AC voltage, DC current, AC current, or ohms and a range switch for accurate readings. The meters may also have other jacks to measure extended ranges of voltage (1 to 5kV) and current (up to 10A). There are some variations to the functions used for specific meters.,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,Fig.3-1 Multimeters,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,The analog meter usually includes the function and range switches in a single switch. It may also have a polarity switch to facilitate reversing the test leads. The needle will have a screw for mechanical adjust to set it to zero and also a zero adjust control to compensate for weakening batteries when measuring resistance. An analog meter can read positive and negative voltage by simply reversing the test leads or moving the polarity switch. A digital meter usually has an automatic indicator for polarity on its display.,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,Meters must be properly connected to a circuit to ensure a correct reading. A voltmeter is always placed across (in parallel) the circuit or component to be measured. When measuring current, the circuit must be opened and the meter inserted in series with the circuit or component to be measured. When measuring the resistance of a component in a circuit, the voltage to the circuit must be removed and the meter placed in parallel with the component.,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,2. Oscilloscope The Oscilloscope presents an accurate electronic picture of the changing voltages within a circuit. An electron beam is created, focused, accelerated and properly deflected to display the voltage waveforms on the face of a cathode-ray tube (CRT). The amplitude of a voltage waveform on an oscilloscope screen can be determined by counting the number of centimeters (cm), vertically, from one peak to the other peak of the waveform and multiplying it by the setting of the volts/cm control. As an example, if the amplitude was 4cm and the control was set on 1V/cm, the peak-to-peak voltage would be 4V.,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,The frequency of a waveform can be determined by counting the number of centimeters, horizontally in one cycle of the waveform and multiplying it by the setting time/cm control. For example, if the waveform is 4cm long and the control is set at 1ms/cm, the period would be 4ms. The frequency can now be found from the formula,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,If the control was went on 100s/cm, the period would be 400s and the frequency would be 2. 5kHz. A dual-trace oscilloscope is advantageous to show the input signal and output signal in the same time, to determine any defects, and indicate phase relationships. The two traces may be placed over each other (superimposed) to indicate better the phase shift between two signals.,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,Exercises .Match the items listed in the following two columns. 1. DC voltage a. 直流电压 2. AC current b. 电池电量不足 3. weakening batteries c. 电压波形 4. polarity switch d. 极性开关 5. voltage waveform e. 交流电流,机械工业出版社 http:/www.cmpbook.com,Passage One Multimeter and Oscilloscope,.Complete the following sentences according to the text. 1. A multimeter is a general-purpose meter capable of measuring and voltage，curr