CiDRA Use of Foundation Fieldbus Protocol with SONARtrac Transmitters - Manual (Page 7)

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FOUNDATION FIELDBUS and PROFIBUS PA
BLOCK DEFINITIONS
2.1 Resource Blocks
Resource blocks contain the hardware specific characteristics
associated with a device; they have no input or output
parameters. The algorithm within a resource block monitors
and controls the general operation of the physical device
hardware. The execution of this algorithm is dependent on the
characteristics of the physical device, as defined by the
manufacturer. As a result of this activity, the algorithm may
cause the generation of events. There is only one resource
block defined for a device. For example, when the mode of a
resource block is “out of service,” it impacts all of the other
blocks.
2.2 Transducer Blocks
Transducer blocks connect function blocks to local input/output
functions. They read sensor hardware and write to effector
(actuator) hardware. This permits the transducer block to
execute as frequently as necessary to obtain good data from
sensors and ensure proper writes to the actuator without
burdening the function blocks that use the data. The
transducer block also isolates the function block from the
vendor specific characteristics of the physical I/O.
2.3 Analog Input Blocks
The Analog Input (AI) function block processes field device
measurements and makes them available to other function
blocks. The output value from the AI block is in engineering
units and contains a status indicating the quality of the
measurement. The measuring device may have several
measurements or derived values available in different
channels. Use the channel number to define the variable that
the AI block processes. The AI block supports alarming, signal
scaling, signal filtering, signal status calculation, mode control,
and simulation. In Automatic mode, the block’s output
parameter (OUT) reflects the process variable (PV) value and
status. In Manual mode, OUT may be set manually. The
Manual mode is reflected on the output status. A discrete
output (OUT_D) is provided to indicate whether a selected
alarm condition is active. Alarm detection is based on the OUT
value and user specified alarm limits.
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