ISA (Instrument Society of America) is an American National Standards Institute (ANSI) accredited orangization. ISA sdministers United States Technical Advisory Groups (USTAG's) and provides secretariat support for International Electrotechnical Commission (IEC) and International Organization for Standardization (ISO) committees that develop process measurement and control Standards.
ISA has laid down a satisfactory system of symbols and identifications for industrial process instrumentation equipments. This provides a uniformity in designating and identifying such equipments on flow plans.