Measurement Of Electrical Quantities and Components

电量和电子元件的测量

Electrical parameters

电参数

Most measurements made on electronic equipment are the parameters of voltage, current, and power. These measurements are usually made during the final product testing phase or incoming testing before the equipment is placed in day-to-day use and Of course during system diagnostic and maintenance stages. Verification of proper operating voltages, current, and power indicate that at least the system has an operational power supply and that power regulation circuits are operating correctly. Oftentimes the main problem with many electronic systems is a poor or defective power supply and by monitoring the power supply electrical parameters, a power supply failure and system outage can be avoided.

对大多数电子设备而言需要测量的是电压，电流，和功率。这些测量通常在产品测试阶段进行，或者在产品即将被日夜使用之前来进行，当然也在系统作诊断和维修期间进行。如果证实操作电压，电流，功率是正常的，那么表明系统至少有一个可供系统运行的能量供应，也表明能量的调节电路是正常运行的。就常规来说，有许多电子的系统的主要的问题是有着不良的或者是有缺陷的能量供但是通过监控能量供应的电子参数，供电失误和系统 停止的情况是可以避免的。

Voltage

电压

One of the easiest measurements to make on a system is voltage. Voltage can be measured using a variety of methods. Instruments used in today’s electronic industry consist of various types of voltmeters with accuracies form 5 percent of full scale to nearly 0.002 percent of reading. Many multimeters used today still use the magnetoelectric meter movement as an indicating device. Many people still feel that a meter showing small flickering changes is easier to read than a digital meter on which you try to read flashing digits. The digital voltmeter has to be powered with a power supply or batteries, while the magnetoelectric type meter only needs a battery in the ohms mode.

在一个系统中，以上最容易测量的就是电压。电压测量可以使用许多方法。当今在电子业使用的测量仪器包括各种各样的电压表，精度从满刻度盘的5%到接近读数的0.002%。今天使用的许多万用表仍在利用电磁表头的运动来作为指示刻度之用。许多人仍然感到在显示出微小摇曳变化的仪表读数比在数字表上竭力去读闪烁的数字更容易。数字式伏特计必须供以能量或者以电池组为动力,而磁电式仪表仅仅在欧姆表里需要一节电池。

It must also be remembered that any voltmeter is a high-impedance device and that an ideal voltmeter draws no current from the circuit being tested. Modern digital voltmeters have input resistances that range from 10 megohms to nearly 10，000 megohms. Also in the AC voltage mode, low-input shunting capacity is necessary for high-frequency operation. The voltmeter is always connected across a circuit or component and one terminal of the voltmeter is always marked either-or common and is usually colored black with a black connecting wire and probe. The other terminal is usually marked + and has a red wire and probe. Some high-frequency AC voltmeters have special hot or + marks on the cables and probes.

我们需要记住的是任何伏特计都是一台高阻抗设备并且一个理想的伏特计是不从被测试的电路分出电流的。现代化的数字伏特计有从10兆欧到10，000兆欧的输入电阻。在AC(交流)电压模式中,低输入的分流容量对高频率的操作运行是必要的。电压表总是跨接电路或者元件的，电压表的一个端口也总是被标记为两用式或公用而且以黑色标记出相连的电线和探头，而另一端通常标以+和伸出红色的线和探头。一些高频交流电压仪有特殊的突出的标记或者+号在线缆和和探头上。

DC voltage measurements

直流电压大小

Solid-state devices are always powered by direct currents and voltages . Vacuum tubes require DC voltage sources as well. Thus many measuremtents are made in the DC mode. Many systems today have built-in diagnostic meters so that power supply parmeters can be monitored and logged.

固体状态设备总是以直流和电压为动力。真空电子管也要求以直流电压为电源。这样许多测量是采用直流模式的。许多系统现在都内装诊断仪以便电能供应参数能被监测和记录。

Accuracies of a typical DC bench-type digital multimeter can be as good as 0.002 percent (1 count of reading for a 6 1/2 digit instrument). This accuracy is often available on the lower voltage ranges usually below 300 V；for higher voltages accuracies may be slightly worse.

一台典型的直流台式数字万用表的精度可以达到0.002%(一种6 1/2 数字仪器的一个读数)。这种精度经常用于低电压范围(一般在300 V以下)；对于更高的电压精确性可能稍微差点。

The point here is to read the instrument’s specifications carefully, and if things are not clearly spelled out, contact the instrument manufacturers’ application. engineering department.

此处的要点是仔细地阅读仪器说明书，如果说明书上没有详细的说明，可与仪器制造商技术支持部门联系。

High-voltage DC measurements usually involve a high-resistance voltage divider, which usually forms a high resistance to the circuit being measured and thus draws infinitesimal current. One common need for measuring DC voltages in the range of 2 to 30 kilovolts(kV)is in measuring cathode-ray tube(CRT) final anode voltages. Many CRTs used in colour television sets and computer monitors have voltages in the range of 15 to 30 kV. The accuracy of such measurements usually is not critical and should be in the range of 3 to 5 percent of the reading. A highly insulated hand-held probe containing the voltage divider is often used and comes as an accessory from some manufacturers.

高压直流测量通常需要一个高阻抗的分压器,它对被测量的电路通常形成一个高电阻以便只有极小的电流被分流。对于测量2到30kV的直流电压，最普通的需要是测量阴极射线管(CRT)的决定电极。许多阴极射线管所包括的彩色显示器和智能探测器有15到30kV的电压。但是用阴极射线管所作测量的精度并不令人有所挑剔，它的精度在读数的3%到5%之间。一种高度绝缘的包括分压器的手持式探头经常被使用而且作为某些设备的附件来配备。