电子技术专业应用unit 3 instruments自制课件.ppt

Instruments Pre-reading Read the following passage, paying attention to the questions. 1. What can be measured with a multimeter? 2. What is the function of an oscilloscope? 3.1.1 Multimeters 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. 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 resistance. 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. 为了保证读数正确，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，必须除去 电路中的电源，万用表与这局部电路（或元 件）并联。 Technical Words and Phrases capable of decibel needle electronic numerical display positive jack common jack function switch range switch variations polarity switch 3. 1. 2 The Digital Oscilloscope UT2000/3000 oscilloscopes offer user-friendly front panel that allows access to all functions easy operation. The scaling of all channels and the positions of buttons are optimally arranged for direct view operation. As design is based on the mode of traditional instr