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英国普利西公司发明的这种电话通讯系统特别适用于煤矿。 由于煤矿存在火灾和爆炸的危险,要求通讯设备必须符合严格的安全规程。例如,井下电池供电通讯网络如扩音电话网络中所允许的最大电流,是由串联在电池输出上的电阻来控制的,这就使网络中的电话机的数目受到了限制。如果需要许多部电话机,那就需要另外组建多个能独自供电的网络。 在这种通讯系统中,井下每个网络的所有电话机除了与井面电话机实现通讯外,还要求网络内的通讯机之间及一个或几个网络间的通讯机之间也能互相通话。然而各网络之间的直接通讯是不允许的,因为这会使网络电流过载,违背安全规程。因此,在井下各网络之间需
This telephony system invented by Pulitzer, UK, is particularly suitable for use in coal mines. Due to the danger of fire and explosion in coal mines, communication equipment must comply with strict safety regulations. For example, the maximum current allowed in a downhole battery-powered communications network, such as a voice over IP telephone network, is controlled by the resistance in series with the battery output, which limits the number of telephones in the network. If you need more than one phone, then you need to set up more than one separate network can be powered. In this kind of communication system, all the telephone sets of each network in the underground not only communicate with the telephone in the well, but also call each other between the communication machines in the network and the communication machines in one or several networks . However, direct communication between networks is not allowed as this will overload the network current and violate safety regulations. Therefore, between the underground network needs