Explain common P&ID instrumentation symbols and tag numbers.

ISA S5.1 defines standard instrumentation symbols. Tag format: First letter = measured variable (F=flow, P=pressure, T=temperature, L=level), succeeding letters = function (I=indicator, C=controller, V=valve, A=alarm, T=transmitter). Examples: FIC=flow indicating controller, LT=level transmitter, PSV=pressure safety valve, TI=temperature indicator. Symbols: circle=field-mounted, square with diagonal=DCS/PLC function, triangle=shared display, dashed line=software link. Instrument lines: solid line=process connection, dashed=electrical signal, dash-dot-dash=pneumatic signal. Understanding these symbols is essential for reading and creating P&IDs.