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6.4 Power fail signal (PF) and power fail 电源故障信号和电源故障 I/O modules maintain the last values until they have recognized the connection interruption and then adopt safety values until the CPU module sends actual values after restart. In case of power failure of the I/O module, output levels adopt zero voltage and/or zero current. I/O模板识别出最后一次值直到它们识别出连接中断，然后采取安全值，直到CPU发送实际值后重新启动。当IO模块断电时，输出零电压和/或零电流。   After voltage returns, I/O modules only change their output level when the CPU module communicates actual values. 恢复电压后，当CPU模板通讯实际值时，I/O模板改变其输出值。   6.4.1Power fail signal (PF) and no power fail 电源故障信号（PF)和断电故障  

PF < 15 ms 电源故障时间 < 15ms

While the power fail signal is active, the CPU module or the AC 800F controller does not communicate current values; I/O modules independently maintain the last values. 当电源故障信号激活，CPU模块或者AC 800F控制器无法通讯当前值；I/O模块 独立的保持前一次的数值。

PF > 15 ms 电源故障时间 > 15ms

I/O modules maintain the last values until they have recognized the connection interruption to the CPU module or to the AC 800F controller before they adopt the configured safety values The safety value are maintained until the AC 800F controller has performed a warm start and provides the I/O modules with new values.  在采取设定的安全值之前，I/O模板保持最近的数值直到识别出与CPU模板或者 AC 800F控制器的连接中断。保持安全值直到AC 800F执行热启动，提供I/O 模板新的数值。

  6.4.2Power fail signal (PF) and power fail 电源故障信号和电源故障 I/O modules maintain the last values until they have recognized the connection interruption and then adopt safety values until the CPU module or the AC 800F Controller provides them with the current values upon restart. In case of power failure of the I/O module, output levels adopt zero voltage and/or zero current. I/O模板保持最近的值直到识别出连接中断。然后采取安全值直到CPU模板或者AC 800F控制器重新启动，提供给它们最新的数值。当I/O模块断电时，输出零电流或者零电压。   When power is supplied again, the I/O modules change their output level only when the CPU module or the AC 800F controller communicates current values. This does not apply to the analog output modules. As long as there is no failure in the external power supply, they keep the last values. Only when the power supply of the AC 800F controller is ensured again, the outputs are de-energized. 当电源恢复，只有当CPU模块或者AC 800F模块通讯当前值时，I/O模块才会改变其输出数值。这不适用于模拟量输出模块，它们保持最近的数值。只有再次确认AC 800F控制器的电源供应时，输出断电。   6.4.3Safety values for field devices 现场设备安全值   The cyclic data exchange between the PROFIBUS master and the connected slaves is monitored. When the cyclic data exchange is interrupted, the safety values can be assumed. The output channels feature manufacturer-specific safety values. Depending on the process requirements, the safety values for input channels can be configured to "Hold the last value" or to a particular value/status. PROFIBUS主站和连接的从站之间的周期性数据交换被监控。当周期性数据交换中断，采取安全值。输出通道采取制造商分配的安全值。根据工艺需求，输入通道的安全值可以配置为“保持最后一次值”或者特定的值/状态。  

A possible power failure can be evaluated by means of a system variable and used in the user program. 可能的电源故障可以通过系统变量来评估，使用在用户程序中。