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    Measurement Of Electrical Quantities and Component
    電量和電子元件的測量(節選)
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    Electrical parameters

    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.

    Voltage

    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.

    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.
    電參數

    對大多數電子設備而言需要測量的是電壓,電流,和功率。這些測量通常在產品測試階段進行,或者在產品即將被日夜使用之前來進行,當然也在系統作診斷和維修期間進行。如果證實操作電壓,電流,功率是正常的,那么表明系統至少有一個可供系統運行的能量供應,也表明能量的調節電路是正常運行的。就常規來說,有許多電子的系統的主要的問題是有著不良的或者是有缺陷的能量供但是通過監控能量供應的電子參數,供電失誤和系統 停止的情況是可以避免的。

    電壓

    在一個系統中,以上最容易測量的就是電壓。電壓測量可以使用許多方法。當今在電子業使用的測量儀器包括各種各樣的電壓表,精度從滿刻度盤的5%到接近讀數的0.002%。今天使用的許多萬用表仍在利用電磁表頭的運動來作為指示刻度之用。許多人仍然感到在顯示出微小搖曳變化的儀表讀數比在數字表上竭力去讀閃爍的數字更容易。數字式伏特計必須供以能量或者以電池組為動力,而磁電式儀表僅僅在歐姆表里需要一節電池。

    我們需要記住的是任何伏特計都是一臺高阻抗設備并且一個理想的伏特計是不從被測試的電路分出電流的?,F代化的數字伏特計有從10兆歐到10,000兆歐的輸入電阻。在AC(交流)電壓模式中,低輸入的分流容量對高頻率的操作運行是必要的。電壓表總是跨接電路或者元件的,電壓表的一個端口也總是被標記為兩用式或公用而且以黑色標記出相連的電線和探頭,而另一端通常標以+和伸出紅色的線和探頭。一些高頻交流電壓儀有特殊的突出的標記或者+號在線纜和和探頭上。
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