The transducer block knows the details of I/O devices and how to actually read the sensor or change the actuator and switches. The transducer block provides the sensor value to the function blocks and/or makes the change in the output as dictated by the function block. Transducer blocks can also perform calibration and linearization.
Transducer blocks are defined to decouple function blocks from the local input/output functions required to read sensor hardware and command effector hardware. This permits the transducer block to execute as frequently as necessary to obtain good data from the sensors without burdening the function blocks that use the data. It also insulates the function block from the manufacturer specific characteristics of an I/O device.
The FOUNDATION Fieldbus specification defines three basic transducer block classes:
1. Input Transducer Block - interface to physical measurements or inputs, processes these measurements and makes its results available to input function blocks through channel reference.
2. Output Transducer Block - interfaces to output function blocks through channel reference and processes their target output to regulate physical actuators or physical outputs.
3. Display Transducer Block - interfaces to local interface devices and allows the local interface access to function block parameters.
Generally, there will be one transducer block per device channel. Multiplexers allow multiple channels to be associated with one transducer block. For some devices, including the National Instruments FP-3000, the functionality of the transducer block is included in the function block. You will not see transducer blocks available for such devices.
Note: There are many parameters that can you can use to modify the I/O functionality.