The most common standard set symbols for instrumentation comes from which organization?

The correct answer is ISA, which stands for the International Society of Automation. This organization is instrumental in establishing widely recognized standards and symbols specifically for instrumentation and control systems. The ISA publishes standards that address the various aspects of automation, including technical terminology, graphical symbols for process control systems, and methodologies for automation practices.

The reason ISA is the most common source for standard set symbols in instrumentation is that it provides a comprehensive framework that is accepted across various industries. This ensures consistent communication and understanding between engineers, technicians, and professionals involved in the design, installation, and maintenance of instrumentation systems.

Other organizations do have their own standards, but they pertain to different aspects of various industries. For instance, NIST (National Institute of Standards and Technology) focuses on physical measurement standards rather than instrumentation symbols. API (American Petroleum Institute) focuses on standards specific to the oil and gas industry, and NEC (National Electrical Code) deals primarily with electrical wiring and safety standards. While these organizations contribute valuable standards, they do not specialize in the standardized symbolism for instrumentation to the extent that ISA does.