Currently, a series of ISO/IEC standards exists
for the drawing of equipment function and control symbols. The revision
of these standards is nearing completion, as is the publication of a
new version of ISO 7000, "Graphical Symbols for Use on Equipment." In
the last publication of this standard in 1985, approximately 1500 symbols
were registered. In the soon-to-be-published document, more than 3000
symbols are defined.
By and large, the symbols appearing in ISO 7000
were developed by industry technical committees to indicate a specific
control function for equipment manufactured by that industry. For example,
TC 23 develops standards for agricultural equipment and creates symbols
for use on combines, tractors, and the like. Over the past decade many
technical committees have found the need to use symbols to communicate
equipment controls and have therefore had to register a symbol with
ISO TC 145 for inclusion in ISO 7000.
The parallel IEC standard to ISO 7000 is IEC
60417, "Graphical Symbols for Use on Equipment." Revised in 1999, this
standard contains 639 electrical function and control symbols. In both
ISO 7000 and IEC 60417, the vast majority of the symbols are highly
abstract: arrows, circles, squares, and straight and wavy lines. The
reason for the standardization of the drawing elements for these types
of symbols is to ensure uniformity and legibility when they are reduced
in size to fit on a control button or panel. The meaning of most of
these symbols is not intuitive; they must be learned.
To qualify for acceptance as a registered symbol
in ISO 7000 or IEC 60417, the proposed symbol must meet three criteria:
the symbol must be drawn according to the rules set forth in ISO/IEC
80416; the symbol must be created in such a way that it will not be
confused with any other symbol; and the symbol must not duplicate a
meaning that already has a registered symbol. There is no requirement
that the symbol be readily understandable.
For specific examples of when to use these symbols,
refer to EN 204, "Safety of Machinery—Electrical Equipment of Machines."
Geoffrey Peckham is president of Hazard Communication
Systems (Milford, PA), a company specializing in the design and production
of product safety labels. For more information, visit http://www.
hazcomsys.com. Peckham is chairman of the U.S. technical advisory
group to ISO TC 145 on graphical symbols. He can be reached at gpeckham@hazcomsys.com.
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