PLC-Course

Lab 06 — Emergency Stop with Safety Relay (Cat 1 Stop)

Sprint: 6 — Design & Safety Time: ~1 hour

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🎯 Brief

Implement the PLC-side logic for a Category 1 controlled stop. Real safety logic lives in a dedicated safety relay or safety PLC — but the standard PLC needs to react correctly when E-stop is pressed:

1. Issue controlled-stop command to the drive
2. After T_Decel_Done (deceleration timer), allow safety relay to remove power
3. Refuse to restart until: E-stop reset AND Reset button pressed AND drive at zero speed

📋 I/O

Tag	Type	Description
EStop_OK	BOOL	Dual-channel E-stop says OK (both channels true)
Reset	BOOL	Manual reset button
Start	BOOL	Start request
Drive_AtZero	BOOL	Drive feedback: speed = 0
T_Decel_Done	BOOL	Deceleration timer elapsed
Drive_Run_Cmd	BOOL	Output: drive run command
Drive_Stop_Cmd	BOOL	Output: controlled stop request
Power_Permit	BOOL	Output to safety relay: OK to keep contactor energized
Ready	BOOL	System ready (idle, awaiting start)
State	INT	0=Faulted, 1=Ready, 2=Running, 3=Stopping

🚦 Transitions

• 0 → 1: EStop_OK AND Reset AND Drive_AtZero
• 1 → 2: Start AND EStop_OK
• 2 → 3: NOT EStop_OK
• 3 → 0: T_Decel_Done OR Drive_AtZero
• Any → 0: NOT EStop_OK in states other than 2 and 3 (already handled)

🛡️ Output Rules

• Drive_Run_Cmd = (State = 2)
• Drive_Stop_Cmd = (State = 3)
• Power_Permit = (State = 1) OR (State = 2) OR (State = 3) — power kept on during deceleration
• Ready = (State = 1)

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