电气专业英语第1单元练习.doc

PART 1 ELECTRONICE 11. Electrical Measuring Instruments Electrical personnel use many different types of measuring instruments. Some jobs require very accurate measurements while other jobs need only rough estimates. Some instruments are used solely to determine whether or not a circuit is complete. The most common measuring and testing instruments are voltage testers, voltmeters, ammeters, ohmmeters, continuity testers（连续性测试仪）, megohmmeters, wattmeters（功率计）, and watt-hour meters（电度表，电表）. All meters used for measuring electrical values are basically current meters. They measure or compare the values of current flowing through them. The meters are calibrated and the scale is designed to read the value of the desired unit.【1】 1.1 SAFETY PRECAUTION Correct meter connections are very important for the safety precaution of the user and for proper maintenance of the meters. A basic knowledge of the construction and operation of meters will aid the user in making proper connections and maintaining them in safe working order.【2】 Many instruments are designed to be used on DC or AC only, while others can be used interchangeably. Note: It is very important to use each meter only with the type of current for which the meter is designed. Using a meter with an incorrect type of current can result in damage to the meter and may cause injury to the user. Some meters are constructed to measure very low values. Other meters can measure extremely high values. CAUTION: Never allow a meter to exceed its rated maximum limit. The importance of never allowing the actual value to exceed the maximum value indicated on the meter can not be overemphasized. Exceeding maximum values can damage the indicating needle, interfere with proper calibration, and in some instances may cause the meter to explode, resulting in injury to the user. Some meters are equipped with over correct protection. However, a current many times greater than the instrument’s design limit may still be hazardous.【3】 2BAS