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HIGH RELIABILITY The redundancy of the module pair, coupled with the high coverage of faults, provides very high subsystem availability time. Either module may be replaced without upsetting field input signals to the other module. A module can be removed or replaced without removing field device termination cabling, power, or communications cabling. REDUNDANT ANALOG INPUTS For each input operation, identical reads are sent to both modules, fully exercising the Fieldbus and the logic circuitry of each module. Each input channel accepts an analog sensor input or a self-powered 4 to 20 mA source. Device power from each module is diode OR’d together in the redundant adapter to ensure redundant power. The microprocessor of each module executes the analog I/O application program, plus security routines that validate the health of the FBM. Input channel security is enhanced by redundantly powering the input current loop from per-channel power supplies in each module of the pair. VISUAL INDICATORS Light-emitting diodes (LEDs) incorporated into the front of the module provide visual indication of the module’s operational and redundancy status, and communication activity on the channels. Two additional LEDs provide the master or tracker status of the modules. FIELDBUS COMMUNICATION A Fieldbus Communication Module or a Control Processor interfaces the redundant 2 Mbps module Fieldbus used by the FBMs. The FBM216 module accepts communication from either path (A or B) of the redundant 2 Mbps fieldbus – should one path fail or be switched at the system level, the module continues communication over the active path. The use of an external power supply common to two or more loops requires a Cable Balun module to maintain communication signal line balance. MODULAR BASEPLATE MOUNTING The module mounts on a modular baseplate which accommodates up to four or eight FBMs. The modular baseplate is either DIN rail mounted or rack mounted, and includes signal connectors for redundant fieldbus, redundant independent dc power, and termination cables. Redundant modules must be located in adjacent positions on the baseplate (positions 1 and 2, 3 and 4, 5 and 6, or 7 and 8). To achieve redundancy, a redundant adapter module is placed on the two adjacent baseplate termination cable connectors to provide a single termination cable connection (see Figure 1). A single termination cable connects from the redundant adapter to the associated termination assembly (TA). TERMINATION ASSEMBLIES Field input signals connect to the FBM subsystem via DIN rail mounted TAs. The TAs used with the FBM216 are described in “TERMINATION ASSEMBLIES AND CABLES” on page 9.