NEC FC-9821X工业工厂计算机
RS485串行端口一个满载的PQM配有三个串行端口。COM1是PQM后端的RS485端口，通常用作系统的主要通信接口。COM2也是一个后置RS485端口，可用于数据收集、打印报告或问题分析，而不会干扰主通信接口。COM3是一个前面板RS232端口，可用于使用EnerVista PQM设置软件进行设定点编程或记录。串行端口提供PQM与远程计算机、PLC或分布式控制系统（DCS）之间的通信功能。在单个通信信道上，多达32个PQM可以与24 AWG绞合屏蔽双绞线菊花链在一起。合适的导线应具有120Ω的特性阻抗（如Belden#9841）。这些电线应远离高功率交流线路和其他电噪声源。通信线路的总长度不应超过4000英尺，以确保可靠运行。正确的极性对通信端口的工作至关重要。
RS485 Serial Ports A fully loaded PQM is equipped with three serial ports. COM1 is a RS485 port available at the rear terminals of the PQM which is normally used as the main communications interface to the system. COM2, which is also a rear RS485 port, can be used for data collection, printing reports, or problem analysis without disturbing the main communications interface. COM3 is a front panel RS232 port that can be used for setpoint programming or recording using the EnerVista PQM Setup software.A serial port provides communication capabilities between the PQM and a remote computer, PLC, or distributed control system (DCS). Up to thirty-two PQMs can be daisy chained together with 24 AWG stranded, shielded, twisted-pair wire on a single communication channel. Suitable wire should have a characteristic impedance of 120 Ω (such as Belden #9841). These wires should be routed away from high power AC lines and other sources of electrical noise. The total length of the communications wiring should not exceed 4000 feet for reliable operation. Correct polarity is essential for the communications port to operate.
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