1. Electrical Measuring Instruments电子测量仪表Electrical personnel use many different types of measuring instruments. 电子技术人员使用许多不同类型的测量仪器。
Some jobs require very accurate measurements while other jobs need only rough estimates. 一些工作需要精确测量面另一些工作只需粗略估计。
Some instruments are used solely to determine whether or not a circuit is complete. 有些仪器被使用仅仅是确定线路是否完整。
The most common measuring and testing instruments are voltage testers, voltmeters, ammeters, ohmmeters, continuity testers, megohmmeters, wattmeters（功率计）, and watt-hour meters（电度表，电表）。
最常用的测量测试仪表有：电压测试仪，电压表，欧姆表，连续性测试仪，兆欧表，瓦特表还有瓦特小时表。
All meters used for measuring electrical values are basically current meters. 所有测量电值的表基本上都是电流表。
They measure or compare the values of current flowing through them. 他们测量或是比较通过他们的电流值。
The meters are calibrated and the scale is designed to read the value of the desired unit. 这些仪表可以被校准并且设计了不同的量程，以便读出期望的数值。
1.1 SAFETY PRECAUTION安全预防Correct meter connections are very important for the safety precaution of the user and for proper maintenance of the meters. 仪表的正确连接对于使用者的安全预防和仪表的正确维护是非常重要的。
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. 仪表的结构和操作的基本知识能帮助使用者按安全工作程序来对他们正确连接和维护。
Many instruments are designed to be used on DC or AC only, while others can be used interchangeably. 许多仪表被设计的只能用于直流或只能用于交流，而其它的则可交替使用。
Note: It is very important to use each meter only with the type of current for which the meter is designed. 注意：每种仪表只能用来测量符合设计要求的电流类型。
Using a meter with an incorrect type of current can result in damage to the meter and may cause injury to the user. 如果用在不正确的电流类型中可能对仪表有危险并且可能对使用者引起伤害。
Some meters are constructed to measure very low values. 许多仪表被设计成只能测量很低的数值Other meters can measure extremely high values.还有些能测量非常大的数值。
CAUTION: Never allow a meter to exceed its rated maximum limit. 警告：仪表不允许超过它的额定最大值。
The importance of never allowing the actual value to exceed the maximum value indicated on the meter can not be overemphasized. 不允许被测的实际数值超过仪表最大允许值的要求再强调也不过分。
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. 超过最大值对指针有伤害，有害于正确校准，并且在某种情况下能引起仪表爆炸造成对作用者的伤害。
Some meters are equipped with over correct protection. However, a current many times greater than the instrument’s design limit may still be hazardous. 许多仪表装备了过载保护。
然而，通常情况下电流大于仪表设计的限定仍然是危险的。
2. Fundamentals of Solid-state Power Device固体功率器件的基本原理In this chapter we focus on solid-state power devices, or power semiconductors,only as they are being used in the power leads or power circuits to three-phase 460 V AC squirrel cage induction motors for either phase (voltage) control or frequency (speed) control. 本章将集中讨论固态功率器件或功率半导体器件，并且只研究它们在采用相控（电压控制）或频率控制（速度控制）的三相交流鼠笼式感应电机的功率电路中的应用。
2.2 SOLID-STATE POWER DEVICES固态功率器件The five major types of power semiconductors used in solid-state AC motor control are: 有五种用于固体交流电机控制中的功率元器件：Diodes二极管Thyristors[e.g., silicon-controlled rectifiers (SCRs)] 晶闸管（例如：可控硅整流器SCR）Transistors电子晶体管Gate-turn-off thyristors门极可关断晶闸管（GTO）Triacs 双向可控硅SCRs and triacs are commonly used for phase controls. 晶闸管SCR和双向可控硅一般用于相位控制（相控）。
Various combinations of diodes, SCRs, transistors, and GTOs are used for speed controls. 各种二极管，晶闸管SCR，电子晶体管，门极可关断晶闸管的联合体用于频控。
The commonality of these devices is the use of crystals of silicon in the form of wafers that are layered so as to form various combinations of PN junction. 这些器件的共性是：利用硅晶体形成的薄片构成P-N结的各种组合。
The P junction is usually called the anode and N junction is usually called the cathode for diodes, SCRs, and GTOs; the corresponding terms for transistors are collector and emitter. 对二极管，SCR， GTO一般P结叫正极N结叫负极；相应的电子晶体管叫集电极和发射极。
The differences among these devices relate to how they go into and out of conduction and in their available ampere and voltage capabilities. 这些器件的区别在于导通和关断的方法及电流和电压的容量。
Let’s take a brief look at each of these devices in terms of these parameters. 让我们根据他们的参数简单看一下这些元器件。
3 Analog Electronics模拟电子3.1 INTRODUCTION介绍3.1.1 The Contrast between Analog and Digital Electronics模拟和数字电子学对照We have already explored how transistors and diodes are used as switching devices to process information which is represented in digital form. 我们已经研究过三极管和二极管怎样作为开关器件用于处理以数字形式出现的信息。
Digital electronics uses transistors as electrically controlled switches: transistors are either saturated or cut off. 数字电子学中，三极管用作电子控制开关：它不是饱和就是截止。