Industry Specific?

Hello everyone,

I would like to hear any opinions regarding how the type of industry relates to the complexity of the overall systems being used. I personally have only worked in a handful of manufacturing plants but have seen a notable difference from one industry to another and am uncertain if this is usually the case. So as an example, is the overall system used in a chemical plant generally more intricate than say an automotive plant or vice versa? Also do the PLC programs used in these industries carry a similar reputation for being more or less complex?

There's an awful lot of variables there even within the same industry. My company is a huge chemical manufacturer, our PLC systems go from complex DCS packages to PLC's programmed as you normally would to control similar processes.

This depends on the age as the newer generation makes use of the available technology.

There's also the risks involved... within the same industry, the same machine can have a simple control system or a top of the line redundant system that is engineered to never fail. The choice of which depends on additional systems linked to this one and also the industry rating for the facility.

A long long time ago, a professor I had in a class about industrial control systems, when describing the difference between a PLC and a DCS put it this way: “A PLC makes ‘things’, a DCS makes ‘stuff’.” For a long time I found that to be generally true. DCS were used in chemical plants, oil and gas processing /refining, pulp and paper mills, brewing etc., where analog measurement and coordinated processing of hundreds or even thousands of PID loops was the paramount activity of the controller. PLCs on the other hand were used in automotive, mining, oil and gas extraction, food processing, machine tools, lumber mills etc. where there was a lot of discrete I/O for positioning sensors, interlocking, user inputs, annunciation, etc. and only a small amount of associated analog I/O and PID loop processing.

Over time the lines have definitely blurred considerably so now you find both types of systems used, sometimes in the same facility and in fact some DCS systems like A-B and Siemens are now comprised of PLCs that are linked together as the I/O sub-processors, and some of the traditional DCS systems moving into doing more PLC-like functions. But industry wise, the lines remain generally the same because of the nature of the tasks; processing of thousands of analog I/O and PID loops requires a lot more number crunching horsepower than traditional PLCs will be capable of, high speed reaction times of machine control to I/O changes and motion control remain the turf of PLCs and PACs (Programmable Automation Controllers, the newer term for higher capability systems).