Are you familiar with these gauge legend symbols?

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The requirements of factory automatic control systems and the control logic design are typically indicated in Process P&ID diagrams using specialized instrument legends and instrument function symbols. It is very helpful for instrument technicians to have a thorough understanding of these legends and symbols in order to carry out their work effectively. 1. Explanation of basic identification letters. 2. Additional letters: XL: RUNNING LAMP – indicator light indicating operation; XV, HV: INTERLOCKED ON/OFF VALVE – two-position valve with interlocking function; KV: TIMER CONTROLLED VALVE – valve controlled by a timer; KC: TIMER – the timer itself; UA: COMMON ALARM – general alarm signal; ESD: EMERGENCY SHUTDOWN – emergency stop function. Regarding the alarm output indicators shown above: HH: EXTRA HIGH LIMIT (higher than the high limit); H: HIGH LIMIT; L: LOW LIMIT; LL: EXTRA LOW LIMIT (lower than the low limit). Instrument symbol legend: yunrun.com.cn/tech/4431.html. 3. The I/P converter to be used is as shown below. 4. Instrument symbol legend: INSTALLED LOCALLY – installed at the site; MOUNTED ON MAIN PANEL – installed on the main control panel; MOUNTED ON LOCAL PANEL – installed at the local control panel; DCS DISPLAY – display on the DCS system; PLC IN CCR – PLC in the control room; PLC IN FIELD – PLC at the field location; INTERLOCK LOGIC – interlocking logic circuit; VENTURI TUBE OR LAVAL NOZZLE – venturi tube or laval nozzle; VARIABLE AREA TYPE FLOW METER – rotameter; VARIABLE AREA TYPE FLOW METER WITH VALVE – rotameter equipped with a valve; STEAM/HOT TRACE OF INSTRUMENT – heating element for the instrument. 5. Symbols for control valve actuators: PNEUMATIC TYPE ACTUATOR (DIAPHRAGM TYPE) – pneumatic actuator of diaphragm type; PNEUMATIC TYPE ACTUATOR (CYLINDER TYPE) – pneumatic actuator of cylinder type; SOLENOID TYPE ACTUATOR – solenoid valve type actuator; ELECTRICAL TYPE ACTUATOR – electric actuator; (CONTROL VALVE) WITH HAND WHEEL – control valve with a handwheel; CLOSE ON AIR FAILURE – closes in case of air supply failure; OPEN ON AIR FAILURE – opens in case of air supply failure; LAST ON AIR FAILURE – remains in its position in case of air supply failure; FAIL POSITION – fault position. 6. Symbols for instrument signal lines: CONNECTION TO PROCESS – connection to the process system; UNDEFINED SIGNAL – undefined signal line; PNEUMATIC SIGNAL – pneumatic signal; ELECTRIC SIGNAL – electrical signal; CAPILLARY TUBING (FILLED SYSTEM) – pressure transfer capillary tube; SOFTWARE OR DATA LINK – internal software signal line or data link; NUCLEAR SIGNAL – signals such as electromagnetic radiation or sound waves. Recommendations for using the instrument symbol legend: Instrument technicians should refer to the standard HG/T 20505-2014 “Functional Indicators and Graphic Symbols for Process Measurement and Control Instruments”. Related readings: ◆ How instrument technicians can understand P&IDs ◆ How instrument technicians can interpret instrument electrical wiring diagrams using naming conventions ◆ Application of SAMA diagrams and their legends in automation design