我的电话线开始的时候用万用表测电压为48V，但现在测的是-48V，两次测量正，负表笔接的线相同，请教这种现象是正常的吗？

这种现像是正常的，因为不管那边是正还是负，后面都有极性定向电路，对于话机来说是没有任何影响的

交换机提供的是-48V 电压。在电话接通后需要提供反极性信号给计费系统，便于计费。

该线路有反极功能,每次拨打电话对方摘机后线路的极性就会反转,对于电话来讲没有任何影响.

普通电话线上也有反极信号吗

BEIJING, Oct. 8 round-up power, on October 7, held from 12 countries more than 50 naval vessels participating in the parade, "an international perspective and ship" into South Korea a few days ago to celebrate the 60th anniversary of the founding of the army and the High tide. South Korean media reports said South Korea is the largest marine parade. By more than 50 warships and more than 30 aircraft participated in the parade ceremony at sea to attract the most attention, to participate in a line of warships, very spectacular scenes.

  
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South Korea, "Korean Daily News" reported that "the international ship-concept" is held in Pusan, South Korea, South Korea 7600 tons of "King Sejong" Aegis destroyers, 14,500 tons of "Dokdo" landing ship, and so on more than 30 The main naval vessels to participate fully demonstrates the current South Korean naval power. In addition, the U.S. also sent its elite fleet to participate in the activities of the military parade.

In addition to Japan, "Bo Ling" destroyer, Russia's "Marshal Shaposhnikov" destroyer, India, "Ranjit" guided missile destroyer, the United Kingdom "echo" of the marine survey ship, Singapore, "adhere to the" landing Ship, Indonesia, "Makassar," landing ship, and other multi-national naval attended the parade. According to media reports, the Chinese navy also sent for the first time, "Harbin" participate in the destroyer.

(China News)
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