电子与通信工程专业英语 教学课件 ppt 作者 徐存善 Unit 4

Unit 4,Multimeters and Oscilloscopes,Multimeters and Oscilloscopes,电子与通信工程专业英语,Multimeters and Oscilloscopes,电子与通信工程专业英语,portable multimeters,dual-trace oscilloscope,1. Multimeters A multimeter 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 (see Fig 4-1(a), and digital, with an electronic numerical display (see Fig 4-1(b). 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 5 kV) and current (up to 10A). There are some variations to the functions used for specific meters,1.万用表 万用表是一种通用仪表，可用来测量直流和交流电压、电流、电阻，有的还能测量分贝（放大倍数的情况）。有两种万用表：一种是用指针在标准刻度上的移动来指示测量值的模拟万用表（见图4-1 a），另一种是用电子数字显示器显示测量值的数字万用表（见图4-2 b）。这两种万用表都有一个正极（+）插孔和一个公共端（-）插孔用来插入测试笔，一个功能选择开关用来选择（测量对象）：直流电压、交流电压、直流电流、交流电流或电阻（欧姆值），一个范围选择开关用来（选择范围）以测出精确读数。万用表还可能有其它插孔用来测量高电压（15kV)和大电流（高达10A），对一些特殊的万用表而言，还会有一些其它功能上的变化。,电子与通信工程专业英语,Besides the function and range switches (sometimes they are in a single switch), the analog meter may have a polarity switch to facilitate reversing the test leads. The needle usually has a screw for mechanical adjust to set it to zero and also a zero adjust control to compensate for weakening batteries when measuring resistanceAn analog meter can read positive and negative voltage by simply reversing the test leads or moving the polarity switchA digital meter usually has an automatic indicator for polarity on its display,除了功能选择开关和范围选择开关（有时它们合成一个开关），模拟万用表可能还有一个极性开关，可以很方便地交换测试笔的极性。通常有一个螺丝可调节指针，（在无电流时）使指针指在零处，另外当测量电阻时一个零点调节控制（钮）用来对电池电压不足时做补偿调节（即保证电阻为0时指针指向零值）。模拟万用表可以测量正电压和负电压，只要简单地对调一下两个测试笔或拨一下极性开关，数字万用表通常会自动在显示器上指示出极性。,电子与通信工程专业英语,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,为了确保读数正确，万用表必须与电路正确连接。一个电压表（万用表测量电压时）应与被测电路或元件并联。当测量电流时，电路必须断开，插入万用表表笔，使万用表与被测电路或元件相串联。当测量电路中局部电路（或元件）的（等效）电阻时，必须关掉电路中的电源，使万用表与该局部电路（或元件）并联。,电子与通信工程专业英语,2. The oscilloscope The oscilloscope (Fig 4-2) is basically a graph-displaying deviceit draws a graph of an electrical signal. When the signal inputs into the oscilloscope, an electron beam is created, focused, accelerated, and properly deflected to display the voltage waveforms on the face of a cathode-ray tube (CRT),2.示波器 示波器（图4-2）是一个图像显示设备，它显示一个电子信号的图像。当信号输入到示波器中时，就产生一个电子束，该电子束被聚焦、加速并适当偏离，在阴极射线管的显示屏上显示电压的波形。,电子与通信工程专业英语,In most applications the graph shows how signals change over time：the vertical (Y) axis represents voltage and the horizontal (X) axis represents time. 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 (Fig 4-3)and the multiplying it by the setting of the volts/cm control. As an example，if the amplitude was 5cm and the control was set on 1V/cm，the peak-to-peak voltage would be 5V,示波器通常显示电压信号如何随时间变化的图像：其垂直轴Y表示电压，水平轴X表示时间。在示波器屏幕上的电压波形的幅度可以通过数出电压波峰与波谷之间纵向距离的厘米值来确定（图4-3）。将这厘米值乘上V/cm控制钮的设定值就得到电压的幅度值。比如说，假若电压的峰-峰间幅度为5cm，控制钮设在1V/cm处，那么，峰-峰电压值为5V。,电子与通信工程专业英语,Time can be measured using the horizontal scale of the oscilloscopeTime measurements include measuring the period，pulse width，and frequencyFrequency is the reciprocal of the period，so once you know the period，the frequency is one divided by the period The frequency of a waveform can be determined by counting the number of centimeters, horizontally, in one cycle of the waveform and the 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 :,用示波器的水平标尺可以测量时间值，时间测量包括测量信号的周期、脉冲宽度和频率。频率是周期的倒数，所以一旦知道了周期，频率就是用1除以周期即可得到。 一个波形的频率可以通过在水平方向数出该波形一个周期的厘米值来确定，将这厘米值乘上时间/厘米控制钮的设定值就得到它的一个周期所需的时间。例如，假定一个波形长4cm，控制钮设在1ms/cm，那么，周期是4ms，则频率可以用下面的公式算出：,电子与通信工程专业英语,f = = = 250Hz If the control was gone on 100/cm, the period would be 400and the frequency would be 2.5kHz. A dual-trace oscilloscope is advantageous to show the input signal and output signal of one circuit 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.,f = = = 250Hz 假定控制钮设在lOO/cm，则周期是400，频率为2.5kHz。 双踪示波器具有同时显示输入信号和输出信号的优点，可以显示输出信号是否有失真和表示输入/输出信号的相位关系，即两路信号的波形重叠在一起可以较好地显示出输入与输出信号相位的差别。,电子与通信