02Level 1
Motor start and stop with seal-in
The most used circuit in industry: NO start button, NC stop button, contactor and thermal overload relay.
Open in the simulator
The simulator is designed for computers (screens 1024 px or wider).
Virtual plant
Contactor K1: de-energized. Overload relay: normal. Speed: 0 %
Shown at rest. In the simulator the plant moves according to your program's outputs.
Inputs and outputs
| Address | Name | Description |
|---|---|---|
| I0.0 | START | Start push button (NO) |
| I0.1 | STOP | Stop push button (NC: 1 at rest) |
| I0.2 | OVERLOAD | Overload relay NC contact (driven by the plant: 0 = tripped) |
| Q0.0 | K1_MOTOR | Motor contactor coil |
Program
Ladder diagram (LD)
Rung 1 — Start with seal-in. STOP and OVERLOAD are NC contacts in the field: they are examined with NO contacts.
Function block diagram (FBD)
Network 1 — Start with seal-in. STOP and OVERLOAD are NC contacts in the field: they are examined with NO contacts.
Structured text (ST)
(* Motor start and stop with seal-in — converted from Ladder *)
(* Rung 1: Start with seal-in. STOP and OVERLOAD are NC contacts in the field: they are examined with NO contacts. *)
K1_MOTOR := (START OR K1_MOTOR) AND STOP AND OVERLOAD;Instruction list (IL)
(* Motor start and stop with seal-in — converted from Ladder *) (* Rung 1: Start with seal-in. STOP and OVERLOAD are NC contacts in the field: they are examined with NO contacts. *) LD START OR K1_MOTOR AND STOP AND OVERLOAD ST K1_MOTOR
Step by step
- 1Press ▶ Run (F5). The STOP input is already 1 because the button is NC.
- 2Press START: the contactor energizes and the motor speeds up. When you release it, the K1_MOTOR contact branch keeps the circuit closed: that is the seal-in.
- 3Press STOP: the input drops to 0, the contact opens and the motor coasts to a stop.
- 4In the “Virtual plant” tab, with the motor running, press “Simulate overload”: the thermal relay opens its contact and the motor stops. It cannot start again until the relay is reset.