Original pneumatic process control loops were implemented with Control in the Field. In those days, the analog input (transmitter) and output (valve) needed to be connected by the air line sharing the 3-15 psi signal calibrated to the transmitter signal. As indicated in past columns, Foundation Fieldbus - with its function blocks - has been designed to be able to implement Control in the Field with the constraint that, like pneumatic loops, the input (AI block) and output (AO block) must be on the same physical segment. In effect, the pneumatic air line has to be replaced with the fieldbus segment wire.
When you talk to safety system and control engineers, many say that they do not have faith in the communications reliability of buses and prefer to use conventional analog signals for all safety applications and SIS (Safety Instrumented Systems). Why? Because, they say, conventional analog signals have been proven in use for so many years. It seems as though these engineers have conveniently forgotten that there was a time when these systems were new as well.
The majority of new electronic field devices being installed today all have some form of diagnostics capability, and most also have some way of communicating their overall general health to another system that can make use of this information to improve overall plant reliability. This reporting system is typically called an asset management system.
Networking technology has been around for at least as long as computers; however, it was not until the 1970s that the demand for permanent connection between distributed nodes became more important.
We are all familiar with the phrase "garbage in, garbage out," but how many of us realize that this statement is also true for our control systems?
We are all aware that the North American energy grid is under stress, and utilities urgently need to manage peak versus off-peak energy demand to reduce the need to build new power plants. One of the ways power-generating companies are deferring the large investment of new plants is through the use of automation - in particular, through Advanced Metering Infrastructure (AMI), which combines Home Area Networks (HANs) and Neighbourhood Area Networks (NANs) as part of the overall Smart Grid initiative.
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