[ P&ID SYMBOLS · STANDARD ]
IEC 62424 P&ID symbols
IEC 62424 sets how process control engineering (PCE) requests are drawn on a P&ID: an oval with letters for what is measured and what is done with it. It is the instrumentation standard on most European P&IDs, used with ISO 10628-2 for the equipment. It also defines CAEX, a data format for passing these requests from the P&ID tool to the control system engineering tools.
- Full title
- IEC 62424, Representation of process control engineering requests in P&I diagrams and data exchange between P&ID tools and PCE-CAE tools
- Latest edition
- IEC 62424:2016, edition 2.0. The first edition, 2008, replaced IEC/PAS 62424 from 2005
- National versions
- EN 62424, DIN EN 62424 (VDE 0810-24):2017-12 in Germany
- Covers
- The PCE request bubble, its letters and reference designation, location of the operator interface, alarms, safety-relevant functions and the CAEX data exchange
- Does not cover
- Equipment symbols. These come from ISO 10628-2
Instruments IEC 62424
About instruments- Field-mounted instrumentLocal PCE request
- Panel-mounted instrumentPCE request in the central control room
- DCS shared displayPCE request in the central control room
- Pressure gaugeLocal pressure indication
- Pressure transmitterPressure indication in the control room
- Level transmitterLevel indication in the control room
- Flow transmitterFlow indication in the control room
- Temperature transmitterTemperature indication in the control room
- Level gaugeLocal level indication
How a PCE request is drawn
Each PCE request is one oval. The letters for the PCE category and processing functions go in the upper half, the request number in the lower half. A horizontal line through the oval means operation and display in the central control room. No line means the function is local, in the field.
IEC 62424 describes the function that is required, not the device that delivers it. There is no letter for transmitter: a pressure measured in the field and shown in the control room is PI with the control room line, where ISA would draw a PT and a PI.
PCE categories and processing functions
PCE category (first letter)
| Letter | Meaning |
|---|---|
| A | Analysis |
| D | Density |
| E | Voltage |
| F | Flow |
| G | Distance, position |
| H | Manual input |
| I | Current |
| J | Power |
| K | Time |
| L | Level |
| M | Moisture |
| N | Electric actuator, for example a motor |
| P | Pressure |
| Q | Quantity, quality |
| R | Radiation |
| S | Speed, frequency |
| T | Temperature |
| V | Vibration, torque |
| W | Weight, force |
| Y | Valve, hydraulic or pneumatic actuator |
| X | Free for other uses |
Processing functions (following letters)
| Letter | Meaning |
|---|---|
| A | Alarm, limit message |
| H, L | Upper and lower limit, for example AH, AHH, AL |
| C | Control |
| I | Indication |
| O | Optical or status display |
| Q | Integration, totalising |
| R | Recording |
| S | Binary control or switching, not safety relevant |
| Z | Binary control or switching, safety relevant |
| Y | Computing function |
Examples: PIC is pressure indication and control, TIRC temperature indication, recording and control, FQI totalised flow, LIZ LL a safety-relevant low-low level function.
IEC 62424 compared with ISA 5.1
| ISA 5.1 | IEC 62424 | |
|---|---|---|
| Bubble | Circle (or square, hexagon, diamond for system functions) | Oval |
| Location | No line field, solid line control room, dashed line behind the panel | No line local, one line central control room |
| Transmitters | Own letter: PT, LT, FT, TT | No letter: the function is shown, for example PI |
| Valves | Succeeding letter V: FV, PV, XV | First letter Y for valves and pneumatic actuators |
| Motors | No dedicated first letter | First letter N for electric actuators |
| Safety functions | Shown with the SIS modifier and interlock symbols | Following letter Z for safety-relevant binary functions |
| Letter Y as first letter | Event, state, presence | Valve, actuator |
Frequently asked questions
What is IEC 62424?
IEC 62424 is the international standard for representing process control engineering requests on P&IDs and for exchanging that data between P&ID tools and control system engineering tools. The current edition is IEC 62424:2016.
Why are instruments drawn as ovals?
Because IEC 62424 draws each process control function, called a PCE request, as an oval. ISA 5.1 uses circles. The oval replaced the circle of the old German DIN 19227.
What does a line through the oval mean in IEC 62424?
Operation and display in the central control room. Without the line, the function is local.
Is IEC 62424 the same as DIN EN 62424?
Yes. DIN EN 62424 (VDE 0810-24):2017-12 is the German edition of IEC 62424:2016.
What is CAEX?
CAEX is the XML data format defined in IEC 62424 for passing PCE requests from the P&ID tool to the tools used to engineer the control system.
The symbols on this page were drawn by Deskely to the forms of the standard and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.
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