PLC Simulator

How to read industrial drawings: schematics, I/O lists and P&IDs

Read a P&ID and an electrical drawing set, follow a signal from the process to a PLC terminal, and document your own work the way an employer expects.

10 units
3 free
2.5 hours
Start free: What a P&ID is, and what it is notSee plans

Training material. Follow your site procedures, local electrical code and the manufacturer's instructions. Lockout/tagout and a qualified person are required for real equipment.

What you will be able to do

  • You can read a P&ID in one pass and tell process pipe from signal line, valve type from valve type, and field instrument from control room instrument.
  • You can decode ISA-style instrument tags such as FIC-101, LT-204 and PSV-310 and say which loop they belong to.
  • You can trace a control loop, including a cascade and a separate alarm loop, from the sensor to the final element.
  • You can follow a wire number through a schematic, wiring diagram, terminal diagram and loop diagram to the PLC channel, and fill in the matching I/O list row.
  • You can name and sort FAT, commissioning and SAT activities, write a usable punch list item and list what an as-built handover contains.
  • You can use a drawing and a few meter readings to find which part of a control circuit has failed.

  1. 01

    What a P&ID is, and what it is not

    Free14 min · lesson

    Read a transfer line out loud, learn the vessel, pump, valve and instrument symbols, and finish by clicking the right symbol on a small P&ID.

  2. 02

    Instrument tags: reading FIC-101 and friends

    Free15 min · lesson

    Decode ISA-style tags letter by letter with an interactive decoder, learn the idioms such as PSV, and finish with a decode-the-tags matching quiz.

  3. 03

    Following a loop from sensor to valve

    Free18 min · lesson

    Trace a pressure loop by hand, then follow the signal on three drawings that grow from a flow loop to a level loop with an alarm to a temperature cascade.

  4. 04

    Four drawings of the same circuit

    Pro12 min · lesson

    See one start-stop circuit as a schematic, wiring diagram, terminal diagram and panel layout, and learn which question each one answers.

  5. 05

    Labels, terminals and cross-references

    Pro14 min · lesson

    Follow wire 104 from a button through terminal X1:4 to a PLC input, then use the cross-reference under a coil to find the other half of relay K1.

  6. 06

    From P&ID tag to PLC address to terminal

    Pro18 min · lesson

    Read a loop diagram for a level transmitter end to end, then fill in the signal type and terminal columns of a mini I/O list.

  7. 07

    Cable schedules and field junction boxes

    Pro11 min · lesson

    Read a cable schedule row, see why instruments share a junction box and a multicore home run, and use both to narrow down damage or a fault.

  8. 08

    Documenting the PLC program: names, comments, structure

    Pro16 min · lesson

    Compare a cryptic rung set with the same logic documented well, and learn naming, why-not-what comments, one writer per output and handover records.

  9. 09

    Commissioning documents: FAT, SAT, punch lists and as-built drawings

    Pro14 min · lesson

    Walk a project from workshop to handover, sort real activities into FAT, commissioning and SAT, and learn what each record contains.

  10. 10

    Troubleshooting from drawings: where do you measure?

    Pro18 min · lesson

    Use the last-good, first-bad method on a series rung, then locate the fault on a graded exercise with four symptoms and meter readings.

Who this track is for

Apprentices, maintenance technicians and new controls engineers who can write a rung but get stuck when handed a drawing set or asked for documentation.

3 of the 10 units are free with a free account, with no card and no expiry. The other 7 are part of a paid plan; compare them on the pricing page.

Related tracks

How do I read an electrical schematic?

Start with the power source, follow each rung or line from left to right, identify every device by its tag, and note which contacts must be closed for the load to energise. Cross-references tell you where the same coil or contact appears on other sheets.

What is a P&ID and why do controls technicians need one?

A piping and instrumentation diagram shows the process equipment, pipes, valves and instruments with their tag numbers. It tells you what each sensor measures and which control loop it belongs to, which is the context you need before you can interpret a PLC input.

What is an I/O list?

It is the table that ties each controller input and output address to a field device, a tag name, a signal type and a terminal. It is the quickest route from a PLC bit to a wire.

How much of Drawings and Documentation is free?

3 of the 10 units are free with a free account, no credit card and no expiry, starting with What a P&ID is, and what it is not. The remaining 7 units are included with a paid plan; see the pricing page for the current plans.

Do I need a PLC or any hardware?

No. Everything runs in the browser against simulated equipment. It is training material: it does not replace supervised practice on real equipment, and lockout/tagout and a qualified person are required for real equipment.

Start with the free units

Browser-based, no install, no hardware.

Start free: What a P&ID is, and what it is not