资源描述
Unit 7 Electronic Instrument Introduction Unit 7 Electronic Instrument Introduction TextK ey wordsTechnical termsExpressionsNotes to the text Unit 7 Electronic Instrument Introduction TextThere are many kinds of Electronic instruments; the leading purpose is to measure various physical quantities such as current, voltage, resistance, temperature, sound level, pressure, etc.Most instruments are delicate, sensitive devices and should be treated with care. Before using an instrument one should be thoroughly familiar with its operation. The best source of information about an instrument is the operating and instructions manual, which is provided with any new instrument purchased. If you are not thoroughly familiar with an instruments operation, specifications, functions, and limitations, read the manual before using the instrument. Unit 7 Electronic Instrument Introduction Here well give the fundamental introductions of some electronic instruments in common use.1OscilloscopeAn oscilloscope can present an accurate electronic picture of the changing voltages within a circuit. It has both advantage and disadvantage when used to measure voltage (or current). The most obvious advantage is that the oscilloscope shows waveform, frequency and phase simultaneously with the amplitude of the voltage (or current) being measured. The VOM or electronic voltmeter shows only amplitude. Likewise, most meters are calibrated in relation to sine waves. Unit 7 Electronic Instrument Introduction When the signals being measured contain significant harmonics, the calibrations are inaccurate. With the oscilloscope, the voltage is measured from the displayed wave, which includes any harmonic content.The only major disadvantage of using an oscilloscope for voltage (or current) measurement is the problem of resolution. The scales of simple inexpensive VOMs or electronic voltmeters are easier to read than an oscilloscope. In most cases, the oscilloscopes vertical scales are used for voltage (or current) measurements, with each scale division representing a given value of voltage (or current). When voltages are large, it is difficult to interpolate between divisions. Unit 7 Electronic Instrument Introduction 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 4 cm and the control was set on 1 V/cm, the peak-to-peak voltage would be 4 V. Usually the peak-to-peak value is required to be converted to RMS, because most voltages specified in electronic maintenance and troubleshooting manuals are RMS.To sum up, if the only value of interest is voltage amplitude, use the meter because of its simplicity in readout. Use the oscilloscope when wave shape characteristics are of equal importance to amplitude. Unit 7 Electronic Instrument Introduction 2. MultimeterA 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, 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 (1-5 kV) and current (up to 10A). There are some variations to the functions used for specific meters. Unit 7 Electronic Instrument Introduction 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. Unit 7 Electronic Instrument Introduction 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. Unit 7 Electronic Instrument Introduction 3. Function Signal GeneratorTake the EE1641B Model function signal generator as an example. The signal generator is a versatile signal source that can be used in a variety of engineering, industrial, educational and hobbyist applications. This generator provides the following types of waveform for output: (1) Sine; (2) Square; (3) Triangle. Unit 7 Electronic Instrument Introduction Press the button below the waveform sketch maps to choose the generated signal of your interests. The wide frequency of the signal generator ranges from 0.2Hz to 2MHz, and the maximum output peak-to-peak value of the signal is 10 volts. So, you should choose the proper “frequency range”button and adjust the“amplitude”knob to obtain the signal you want from the “50 ”output terminal. The attenuation buttons“20 dB”and“40 dB”are needed for the signal which amplitude is small than 1 volt. Unit 7 Electronic Instrument Introduction Besides the function of generate the three kinds of waveforms given above, this signal generator is also a counter or a scanner. It may be used in external sweeping and counting, here no more unnecessary details will be given. Unit 7 Electronic Instrument Introduction Key wordsquantity n. 量，数量pressure n. 压，压力，电压delicate adj. 精密的sensitive adj. 灵敏的instruction n. 指示，说明(书)，指令manual n. 手册，指南purchase vt./n. 买，购买specification n. 详述，规格，说明书，规范limitation n. 限制，局限性accurate adj. 正确的，精确的 phase n. 相位voltmeter n. 伏特计 Unit 7 Electronic Instrument Introduction calibrate v. 校准sine n. 正弦significant adj. 有意义的，重大的，重要的harmonic n. 谐波oscilloscope n. 物示波器resolution n. 分辨率verticaladj. 垂直的divisionn. 分开，分割centimetern. 厘米scalen. 刻度，进制interpolatev. 插入 maintenance n. 维护，保持decibeln. 分贝 Unit 7 Electronic Instrument Introduction jackn. 插孔，插座polarityn. 极性facilitatevt. 使容易，使便利compensatev. 偿还，补偿battery n. 电池parallel adj. 并联的series n. 串联generatorn. 发电机，发生器versatileadj. 通用的，万能的triangle n. 数三角形attenuation n. 衰减 scanner n. 扫描器，扫描仪 Unit 7 Electronic Instrument Introduction Technical termsVOM 电子伏特表peak-to-peak value峰-峰值RMS (root-mean-square) 均方根值(有效值)troubleshooting manuals故障手册general-purpose meter通用仪表function signal generator 函数信号发生器 Unit 7 Electronic Instrument Introduction Expressionsbe familiar with对熟悉in relation to 与有关；涉及multiplyby 用乘be converted to把转换成be capable of 能够in parallel with 与并联takeas an example 以为例ranges fromto 从到的范围 Unit 7 Electronic Instrument Introduction Notes to the text1. 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.示波器屏幕的电压幅值可以通过峰-峰值所占垂直格数乘上所设定的volts/cm控制旋钮来确定。句中的“counting”与“multiplying”为并列部分，同为介词“by”的宾语。“multiplyby”为词组。 Unit 7 Electronic Instrument Introduction 2. There are two types of meters: analog, using a standard meter movement with a needle, and digital, with an electronic numerical display.有两种类型的万用表：使用标准仪表指针的模拟式万用表和使用电子数字显示的数字式万用表。句中，“analog”与“and digital”为并列成分，承前省略中心词“meters”；“using a standard meter movement with a needle”为现在分词短语作后置定语修饰“analog”；“with an electronic numerical display”为伴随状语。
展开阅读全文