系统压力或差压变送器信号输出采用HART现场总线协议，数字信号传输通过RS485进行MODBUS通讯。

HART field-bus protocol is used in output of system pressure or differential pressure transmitter, digital signals is transmitted with MODBUS via RS485.

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分析了B码的对时机理，指出变电站的智能设备采用B码对时，就不再需要现场总线的通信报文对时，也不再需要GPS输出大量脉冲接点信号。

The synchronization principle of IRIG-B code is analyzed. When applying IRIG-B code in substation IED, neither communication messages of fieldbus nor multiple pulse signals of GPS are needed.

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