PLC Time Relay Ladder Diagram Example (IEC 61131-3 TON / TOF / TP, 2026)
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PLC Time Relay Ladder Diagram Example (IEC 61131-3 TON / TOF / TP, 2026)
A PLC time relay ladder diagram is still the fastest way to ship a deterministic delay on a conveyor, a pump, or a heating zone. This 2026 update rewrites the classic TON example using the IEC 61131-3 timer block family and shows how Allen-Bradley, Siemens, Mitsubishi, Omron, Schneider, and Mitsubishi-FX rung-by-rung programming compare against the new Structured Text (ST) shortcut.
Detail
TON, TOF, and TP cover 90% of time relay logic; use TP for pulse, TOF for off-delay.
A safe rung always closes a NC contact in parallel to the start signal as a watchdog.
IEC 61131-3 timers port across Allen-Bradley, Siemens, Mitsubishi, Omron, and Schneider with only tag-mapping changes.
Time bases in 2026 firmware default to 1 ms for AB CompactLogix and Siemens S7-1500, so scale old projects.
For new code, add a TON done-bit seal-in around the output instead of latching an output coil.
2026 walk-through of a 10s conveyor start-delay using IEC 61131-3 TON/TOF/TP, brand tag names, and a new Structured Text shortcut for AB, Siemens, Mitsubishi, and Omron.
Time-delay relays used to be electromechanical devices bolted to a DIN rail. In 2026, the equivalent logic is a software timer function block running on a PLC scan, but the engineering discipline has not changed: define the inputs and outputs, prove the timing, and only then draw the rungs. The IEC 61131-3 standard defines three timer blocks that cover almost every time relay diagram on a factory floor today.
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