National Instruments FP-3000 - Manual (Page 54)

Chapter 4 Block Reference
FieldPoint FP-3000 User Manual 4-2 www.ni.com
communication between function blocks on different devices are scheduled
deterministically.
A PID control loop consists of one of each of the following function blocks:
an Analog Input (AI) block to read the process variable in a device (such as
a transmitter), a Proportional–Integral–Derivative (PID) block to compare
the process value to the setpoint and make control decisions, and an Analog
Output (AO) block to move an actuator in a device (such as a valve). The
PID can be located (and execute) in the transmitter, valve, or any other
device (such as a controller). The execution of the AI, PID, and AO blocks
is precisely scheduled on a schedule. The communication of the process
value from the AI to the PID and the communications between the PID and
AO blocks are also scheduled and synchronized with the block executions.
The FP-3000 function blocks conform to the standard function blocks
defined by the F
O U N D A TIO N Fieldbus. In addition, the FP-3000 contains
certain enhancements to the standard function blocks, such as AI, AO, DI,
and DO, to permit easy configuration and diagnostics. The FP-3000 also
uses National Instruments defined function blocks. All the vendor-specific
blocks and enhancements are defined using Device Descriptions to
interoperate with other hosts and devices.
Transducer Blocks
Transducer blocks read from physical sensors into function blocks.
Transducer blocks decouple the function blocks from the hardware details
of a given device, allowing generic indication of function block input and
output.
The transducer block knows the details of I/O devices and how to actually
read the sensor or change the actuator. The transducer block performs the
digitizing, filtering, and scaling conversions needed to provide the sensor
value to the function blocks and/or makes the change in the output as
dictated by the function block. Generally, there will be one transducer block
per device channel. In some devices, multiplexors allow multiple channels
to be associated with one transducer block.
Manufacturers can define their own transducer blocks. For some devices,
including the National Instruments FP-3000, the functionality of the
transducer block is included in the function block. You will see no separate
transducer blocks for such devices.
Note There are many parameters that can be changed to modify the I/O functionality.