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2-9GFK-0787B Chapter 2 Input Subsystem
Analog Inputs
Like discrete blocks, analog blocks can be used in the input subsystem as members of
GMR input groups of 1 to 3 blocks, or as non-voted blocks. Also like discrete blocks,
individual circuits of analog blocks in multiple-block GMR input groups can be used as
non-voted analog inputs.
Analog blocks in GMR input groups are not autotested by the GMR software.
All of the available types of analog blocks can be used, including the Thermocouple and
RTD blocks. See the Genius I/O Discrete and Analog Blocks User’s Manual for information
about the various analog Genius blocks.
The application program can reference all analog inputs directly, whether they are
located in the non-voted analog inputs area or not.
Voted Analog Inputs
For voted analog inputs, analog blocks must be set up as 2-block or 3-block input groups.
The input values are in engineering units.
For a 3-block group, the GMR software compares the three corresponding inputs for
each channel and selects the intermediate value. This value is made available to the
application program. The application program can also access the original input values.
Field Input Data
Input A
Input B
Input C
152
150
110
PLC Selects the
Intermediate Value
150
Single Input Provided
to Application Logic
For example, in the illustration above, inputs A, B, and C might represent the first
channel on each block in a three-block group. The PLC would place the selected input
value into the first voted input word for that group.
Number of Input Sensors per Voted Channel
For each voted input channel in a 3-block group, either single or triple input sensors that
are compatible with the input drive requirements of the Genius blocks can be used.
Current-loop (4-20mA) devices must be converted to voltage when a single sensor is
used.
Analog Voting Adaptation
If a failure (discrepancy fault, or Genius fault) occurs, the GMR software rejects the
faulty data. Depending on the configuration of the input group, input voting may go
from three inputs to two inputs to one input, or from three inputs to two inputs to the
configured default value.