PLC-Course

Lab 02 — Conveyor Sort by Height

Sprint: 3 — Ladder & FBD (uses early shift register concept previewed) Languages allowed: ST or LD Time: ~90 minutes

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🎯 Brief

A conveyor moves boxes past two photoelectric sensors. The lower sensor detects every box; the upper sensor only detects “tall” boxes. A reject solenoid 4 conveyor positions downstream pushes tall boxes off the line.

You need to:

1. Detect a box at the inspection point
2. Determine if it’s tall (upper sensor active when lower also active)
3. Track which conveyor positions hold a tall box
4. Fire the reject solenoid for one scan when a tall box reaches the reject position

📋 I/O List

Inputs

Tag	Type	Description
Sensor_Low	BOOL	Lower photo-eye (any box present)
Sensor_High	BOOL	Upper photo-eye (tall box present)
Index_Pulse	BOOL	Conveyor index (one pulse per position advance)
EStop	BOOL	Emergency stop (NC, fail-safe — true when OK)

Outputs

Tag	Type	Description
Reject_Sol	BOOL	Reject solenoid (pulse high for one scan when needed)
Tall_Detected	BOOL	Status — tall box detected at inspection point

Internal state

Tag	Type	Description
Track_P0	BOOL	Inspection position
Track_P1	BOOL	One position downstream
Track_P2	BOOL	Two positions downstream
Track_P3	BOOL	Three positions downstream
Track_P4	BOOL	Reject position
Last_Index	BOOL	For edge detection on Index_Pulse

💡 Hints

• Use Track_P0..P4 as a manual shift register — on the rising edge of Index_Pulse, shift the values along.
• Tall_Detected is true only when both sensors are active in the same scan.
• Reject_Sol should fire when Track_P4 is true.
• EStop should clear all tracking when false.

Submit your solution as solution.st.

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