Lesson 3 - Principles of Process Control SAQ
This lesson allows you to test yourself on the material covered in the Principles of Process Control lesson and determine the level to which you have met the learning outcomes.
Suggested Response - Q6
** What is meant by fieldbus protocol and conventional wiring? Compare the two systems.
Response:
Conventional wiring is where each device has its own set of wiring that must be wired to a digital input or output card and then to the control system.
Fieldbus protocol allows for many devices to connect to a single network. Data can also be sent in both directions.
Fieldbus requires less wiring and can send a greater amount of information. Fieldbus allows multiple parameters to be obtained from a single device. Intelligent devices can be used that allow setup from the control system but will continue on their control loop should communication with the PLC be lost. Fieldbus signals are fast and signal quality is not affected in the same way that a 4-20 mA signal is.
The obvious downside to a fieldbus system is the cost. Not only are the communication interfaces more expensive, but the instrumentation is also. However, they do have a greater capacity. For a smaller brewery in particular, a fieldbus is an expensive choice.