LADDER LOGIC, SCI-FI WISE
I need a life. Too many of my idle hours are spend on the 'net. But my time is not totally wasted. Some browsing in the automation bulletin boards indicates that ladder logic, the PLC language, needs some work. The original ladder logic was discovered (invented?) in the late 60's by the group that started Modicon. We sought to introduce real time, user-friendly software to industry. The only available languages at that time were based on icons or flow charts.
One priority in designing the interface was that it had to be intuitive, for use without training. The only significant change since that time has been the addition of cells, or function blocks.
Define one way, ladder logic is a symbolic representation of what amounts to control circuit. The power lines form the sides of a ladder like structure, with the program elements arranged to form the rungs.
Expressed another way, ladder logic incorporates computational agents with convergent transforms. The database is composed of outputs from agents and sensor inputs. The agents examine the blackboard database independently for subsequent execution. It is predictable, inherently robust, and fast enuff.
Rather than abandon ladder logic in favor of computer programming languages, such as Basic or C++, we should make the first significant upgrade to ladder logic in several decades. By incorporating a range of suggestions, we can resist the temptation to yield to the beckoning of "Windows99."
To do so, a committee of august citizens will be drawn from the MAP, Pentium, Denver baggage, OMAC, and Waco teams. The committee will be charged with incorporated into ladder logic such things as virtual reality, holographic databases, floating point math, public key encryptions for I/O, and full preemptive multitasking.
The new ladder logic will allow extensive subsets. Nothing will be defined, to allow each user the greatest possible freedom. It will be the first politically correct computing language, with blame always assigned early in each implementation and enforced by the standards committee. One potential, unforeseen benefit of this approach is that each company will finally have a proprietary standard to ensure user loyalty.
Technically, ladder logic is NOT a "go-to" language. It is more "come-from" and, in the Boolean sense, uses the "if-then" concepts. But these are modern times and we can today do better. Suggestions gathered by means of an informal survey include incorporation of such concepts as these:
Many such improvements are being considered by the committee. In addition, we will look at traditional uses of ladder logic. Function blocks are typically timers and counters. This can be taken to a whole 'nother level. For example, resumes can be automatically generated based on the density of bugs in a given program. Or overhead presentations can be generated based on project overrun statistics.
Finally, since some seem to think factories will one day be run by word processors, we'll counterattack "Word" dominance with "Ladder," thus ensuring an unlimited future for the MBAs of Cambridge. We're also petitioning the U.S. Department of Defense to send the language, free of charge, to our friends in Iran and Iraq.
Job creation resulting from support of these standards will be greater than any Porkware project ever imagined. Much like any other standard creating body, we will measure progress by number of spec sheet pages produced watch month. At the conclusion of years of work we will be in position to thanks the committee for the work done thus far, and to encourage others to join in helping make the reality a dream.
As appeared in Manufacturing Systems Magazine July 1995 Page 14
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