Process Automation Through 50 Years in History

We've Come a Long Way in 50 Years and Automatic Safety Controls Are the Airbags of the Industry

By Bela Liptak

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Now the time is ripe to adopt a worldwide standard for a digital communication protocol, a standard that could link all the digital "black boxes," and could also act as a "translator" for those older instruments that were not designed for the digital age. Naturally, this standardization will allow the easy mixing of different manufacturers' products in our control systems.

A major step in this direction was taken in 2011, when the five major automation foundations agreed to unite around one protocol for field device integration (FDI). They agreed to combine their efforts, and form a joint company, FDI Cooperation. Its "board of managers" is composed of representatives of the five automation foundations and the managers of global automation equipment suppliers. (See "Swimming in the Alphabet Soup of Device Management").

We have good reason to hope that the FDI will finally end the Babel of communication protocols. When this materializes, the automation and process control engineers can once again concentrate on designing safe and optimized control systems, and stop wasting their time figuring out the communication among black boxes of the different suppliers.

Smart Instruments, Soft Sensors

Another step in the right direction is the availability of multiple sensor ranges, multiple references and the built-in intelligence serving to switch among them.

Sensor improvements also include the ability to switch between wired and wireless data transmission, providing both local and remote displays of both the real-time readings of variables and their past history, or providing self-diagnostics that signal the need for maintenance, recalibration or to report sensor failure.
Soft sensors are detectors that don't directly measure variables, but obtain measurements through the evaluation of other variables. For example, the mass of water in a boiler can be obtained indirectly on the basis of material balance between the water entering and the steam leaving. Similarly, outflow from a tank can be obtained from the rate of level change or from pump speed and pump power consumption. The mass flow of gases can be obtained from orifice ΔP, upstream pressure and gas temperature, or in custody transfer of oil, while mass flow can be obtained from volumetric flowmeters by using compensation algorithms for density.

Accuracy, Rangeability

It is also a major step forward that the best manufacturers now include the basis of their accuracy and rangeability statements in their specifications, and independent testing organizations, such as Evaluation International, are used to confirm them. The best manufacturers are also defining rangeability as the ratio between those maximum and minimum readings for which the claimed accuracy statement is still valid.

Similarly, nowadays the best control valve manufacturers' literature defines the rangeability of their valves as the range over which they guarantee that the specified valve characteristics are maintained within 25%. This is usually between 5% and 85% or so.

In short, there is no profession with a brighter future and a better ability to contribute to human progress than ours. 

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