将所有三个FIU连接到单个现场设备。FTU主要包括
前端信号调节、现场信号所需的无源元件
过压保护和EMI/RFI滤波。当安装在受信任的
控制器或扩展器机箱，FTU现场连接器互连至
连接在机箱后部的输入/输出电缆组件。
SmartSlot链接通过从HIU传递到现场连接
FTU。这些信号直接传输至输入/输出电缆组件并进行维护
与FTU上的输入/输出信号隔离。SmartSlot链接是智能的
活动和备用模块之间的连接，以便在
模块更换。
现场接口单元（FIU）是模块的一部分，包含
与特定类型的现场输入/输出接口所需的特定电路
信号。每个模块有三个FIU，每个片一个。对于TMR 24 Vdc数字
输入模块，FIU包含一个单独的模数（A/D）转换器
对于40个现场输入中的每一个。
FIU从HIU接收逻辑隔离电源。金融情报室提供
针对
FIU电路。一个隔离的6.25 Mbit/s串行链路将每个FIU连接到
HIU切片。
FIU还测量一系列机载“内务”信号，以协助
监控模块的性能和运行条件。
这些信号包括电源电压、电流消耗、车载
参考电压和电路板温度。
The Field Termination Unit (FTU) is the section of the I/O Module that connects all three FIUs to a single field device. The FTU primarily contains passive components necessary for front-end signal conditioning, field signal overvoltage protection, and EMI/RFI filtering. When installed in a Trusted Controller or Expander Chassis, the FTU field connector interconnects to the I/O cable assembly attached at the rear of the Chassis. The SmartSlot link is passed from the HIU to the field connections via the FTU. These signals go directly to the I/O cable assembly and maintain isolation from the I/O signals on the FTU. The SmartSlot link is the intelligent connection between Active and Standby Modules for coordination during Module replacement. The Field Interface Unit (FIU) is the section of the Module that contains the specific circuits necessary to interface to the particular types of field I/O signals. Each Module has three FIUs, one per slice. For the TMR 24 Vdc Digital Input Module, the FIU contains an individual analog to digital (A/D) converter for each of the 40 field inputs. The FIU receives isolated power from the HIU for logic. The FIU provides additional power conditioning for the operational voltages required by the FIU circuitry. An isolated 6.25 Mbit/s serial link connects each FIU to one of the HIU slices. The FIU also measures a range of onboard “housekeeping” signals that assist in monitoring the performance and operating conditions of the Module. These signals include power supply voltages, current consumption, onboard reference voltages and board temperature.
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