FBM208 冗余模拟输入

Description

FBM208 冗余模拟输入

FBM208 冗余模拟输入

Single input/single output control schemes with high availability requirements can takeadvantage of the FBM208 arranged as a redundant pair. A readback feature isprovided that detects failures of the output channel. In a repair situation, when a singlemodule is replaced, the inputs and outputs are maintained by the redundant module. HART® signals are electrically compatible with the 4-20 mA signals, permitting theplant to upgrade field devices without the need to change the control system. TheFBM208b provides the same functionality and is used to upgrade from the olderFBM05.

A redundant pair of the modules combine to provide redundancy at the FieldbusModule (FBM) level, with field I/O wired to one common termination assembly (seeFigure 1, page 4). Each module independently attempts to hold the output(s) at itsspecified output value(s), and each independently reports its observed value of theinputs.

A redundant analog input and redundant analog output block in the Foxboro™ DCSControl Software validates each input and output in conjunction with information to/from the module.

The FBM208 is electrically compatible with standard HARTsignals.

Features:

• Four 0 to 20 mA dc analog input channels
• Four 0 to 20 mA dc analog output channels with readback
• Compares FBM’s output value with the current readback value. If the readbackvalue differs from the desired output by more than ± 2%, the FBM marks itsoutput channel BAD
• Monitors FBM’s internal channel current loop power and marks the channel BADif power is less than 16 V dc
• Marking a channel Bad causes the corresponding channel in the redundantmodule to continue to drive the outputs
• Redundant modules increase reliability
• Termination Assemblies (TAs) for locally or remotely connecting field wiring to theFBM208