Glossary · ST
What is Structured Text (ST)?
A textual programming language in IEC 61131-3 resembling Pascal, used for complex PLC logic, calculations and state machines.
It supports IF, CASE, FOR and WHILE, and function blocks such as the TON timer and CTU counter. Siemens TIA Portal calls it SCL.
A simple example: Pump := Start AND NOT Stop AND Level < 90.0; try writing a full program and running it in the ST Lab.
Related terms
- Programmable logic controller (PLC)
- An industrial computer built to control machines and processes: it reads sensors and switches, runs the control program, and drives motors and valves, repeatedly and reliably.
- PID controller
- A control algorithm that computes its output from the difference between the setpoint (SP) and the measured value (PV), in three parts: proportional, integral and derivative.