Conveyor sorting system in PLC Programming - Mini Project: Build & Apply

Conveyor sorting system

📖 Scenario: You are programming a conveyor sorting system in a factory. The conveyor moves items, and sensors detect the item type. Based on the type, the system activates different sorting arms to direct items to the correct bins.

🎯 Goal: Build a simple PLC program that reads item types from sensors, uses a configuration threshold to decide sorting, and activates the correct sorting arm outputs.

📋 What You'll Learn

Create a variable to hold the current item type detected by the sensor

Create a configuration variable for the sorting threshold

Use a conditional statement to decide which sorting arm to activate based on the item type and threshold

Output the activation signal for the correct sorting arm

💡 Why This Matters

🌍 Real World

Conveyor sorting systems are common in factories to automate sorting of products by type, size, or quality. PLC programs control sensors and actuators to perform this task efficiently.

💼 Career

Understanding how to program sorting logic in PLCs is essential for automation engineers working in manufacturing and industrial automation.

1

Set up the item type variable

Create a variable called itemType of type INT and set it to 3, representing the detected item type.

PLC Programming

# Create an INT variable named itemType and set it to 3
# Your code here

Hint

Use the VAR block to declare variables. Set itemType to 3.

2

Add sorting threshold configuration

Add a variable called sortingThreshold of type INT and set it to 2. This will be used to decide sorting logic.

PLC Programming

VAR
    itemType : INT := 3; // Detected item type
    // Declare sortingThreshold INT variable and set to 2
    // Your code here
END_VAR

Hint

Declare sortingThreshold in the same VAR block as itemType.

3

Implement sorting logic

Write an IF statement that checks if itemType is greater than sortingThreshold. If true, set a BOOL variable activateArm1 to TRUE, else set activateArm2 to TRUE. Declare both BOOL variables before the IF statement and initialize them to FALSE.

PLC Programming

VAR
    itemType : INT := 3; // Detected item type
    sortingThreshold : INT := 2; // Threshold for sorting
    activateArm1 : BOOL := FALSE; // Sorting arm 1 activation
    activateArm2 : BOOL := FALSE; // Sorting arm 2 activation
END_VAR

// Write IF statement to activate correct arm
// Your code here

Hint

Use IF...THEN...ELSE to compare itemType and sortingThreshold. Set the BOOL variables accordingly.

4

Output the sorting arm activation

Write code to output the values of activateArm1 and activateArm2 to the console using WriteLn statements. Output exactly these two lines: WriteLn("Arm1 Active: ", activateArm1); and WriteLn("Arm2 Active: ", activateArm2);

PLC Programming

VAR
    itemType : INT := 3; // Detected item type
    sortingThreshold : INT := 2; // Threshold for sorting
    activateArm1 : BOOL := FALSE; // Sorting arm 1 activation
    activateArm2 : BOOL := FALSE; // Sorting arm 2 activation
END_VAR

IF itemType > sortingThreshold THEN
    activateArm1 := TRUE;
    activateArm2 := FALSE;
ELSE
    activateArm1 := FALSE;
    activateArm2 := TRUE;
END_IF;

// Output the activation states
// Your code here

Hint

Use WriteLn to print the BOOL variables with the exact text.

Practice

1. In a conveyor sorting system, what is the main role of sensors?

easy

A. To power the entire system

B. To move the conveyor belt forward

C. To detect items and send signals for sorting decisions

D. To clean the conveyor belt automatically

Solution

1. Step 1: Understand sensor function in sorting

   Sensors detect the presence or type of items on the conveyor.

2. Step 2: Connect sensor signals to sorting

   The system uses sensor signals to decide where to send each item.

3. Final Answer:

   To detect items and send signals for sorting decisions -> Option C

4. Quick Check:

   Sensors detect items = C [OK]

Hint: Sensors detect items to guide sorting [OK]

Common Mistakes:

• Confusing sensors with motors
• Thinking sensors power the system
• Assuming sensors clean the belt

2. Which of the following is the correct syntax for a simple IF statement in PLC ladder logic to check if a sensor is ON?

easy

A. IF Sensor1 = TRUE THEN Conveyor := ON;

B. IF (Sensor1 == ON) { Conveyor = ON }

C. IF Sensor1 THEN Conveyor ON;

D. IF Sensor1 = ON THEN Conveyor := ON;

Solution

1. Step 1: Identify correct PLC syntax

   PLC languages often use ':=' for assignment and 'THEN' for conditions.

2. Step 2: Check sensor condition and assignment

   IF Sensor1 = TRUE THEN Conveyor := ON; uses 'Sensor1 = TRUE' and 'Conveyor := ON;' which matches PLC style.

3. Final Answer:

   IF Sensor1 = TRUE THEN Conveyor := ON; -> Option A

4. Quick Check:

   Correct PLC IF syntax = A [OK]

Hint: Look for ':=' assignment and 'THEN' keyword [OK]

Common Mistakes:

• Using '==' instead of '='
• Missing ':=' for assignment
• Using curly braces which are not PLC style

3. Given the following PLC code snippet for a conveyor sorting system:

IF SensorA = TRUE THEN
  Diverter := LEFT;
ELSE
  Diverter := RIGHT;
END_IF;

What will be the value of Diverter if SensorA is FALSE?

medium

A. LEFT

B. FALSE

C. TRUE

D. RIGHT

Solution

1. Step 1: Analyze the IF condition

   The code sets Diverter to LEFT if SensorA is TRUE.

2. Step 2: Determine ELSE action when SensorA is FALSE

   When SensorA is FALSE, Diverter is set to RIGHT.

3. Final Answer:

   RIGHT -> Option D

4. Quick Check:

   SensorA FALSE leads to Diverter RIGHT [OK]

Hint: FALSE condition triggers ELSE branch [OK]

Common Mistakes:

• Assuming Diverter stays unchanged
• Confusing TRUE and FALSE branches
• Mixing variable names

4. Identify the error in this PLC code snippet for sorting items:

IF Sensor1 = TRUE THEN
  Conveyor := ON
ELSE
  Conveyor := OFF;
END_IF;

medium

A. Missing semicolon after 'Conveyor := ON'

B. Incorrect use of ELSE statement

C. Sensor1 should be compared with FALSE

D. Assignment operator ':=' is invalid

Solution

1. Step 1: Check statement endings

   Each assignment line in PLC code must end with a semicolon.

2. Step 2: Locate missing semicolon

   The line 'Conveyor := ON' lacks a semicolon at the end.

3. Final Answer:

   Missing semicolon after 'Conveyor := ON' -> Option A

4. Quick Check:

   Semicolon missing = D [OK]

Hint: Check each line ends with semicolon [OK]

Common Mistakes:

• Ignoring semicolon errors
• Misreading ELSE syntax
• Thinking ':=' is wrong assignment

5. You want to program a conveyor sorting system that directs items to three paths: LEFT, CENTER, or RIGHT based on two sensors: SensorX and SensorY.

If SensorX is TRUE and SensorY is FALSE, send to LEFT.
If SensorX is FALSE and SensorY is TRUE, send to RIGHT.
Otherwise, send to CENTER.

Which PLC code snippet correctly implements this logic?

hard

A. IF SensorX = TRUE OR SensorY = FALSE THEN
Diverter := LEFT;
ELSEIF SensorX = FALSE OR SensorY = TRUE THEN
Diverter := RIGHT;
ELSE
Diverter := CENTER;
END_IF;

B. IF SensorX = TRUE AND SensorY = FALSE THEN
Diverter := LEFT;
ELSIF SensorX = FALSE AND SensorY = TRUE THEN
Diverter := RIGHT;
ELSE
Diverter := CENTER;
END_IF;

C. CASE
WHEN SensorX = TRUE AND SensorY = FALSE THEN Diverter := LEFT;
WHEN SensorX = FALSE AND SensorY = TRUE THEN Diverter := RIGHT;
ELSE Diverter := CENTER;
END_CASE;

D. IF SensorX = TRUE THEN
Diverter := LEFT;
ELSEIF SensorY = TRUE THEN
Diverter := RIGHT;
ELSE
Diverter := CENTER;
END_IF;

Solution

1. Step 1: Match conditions to logic

   IF SensorX = TRUE AND SensorY = FALSE THEN
     Diverter := LEFT;
   ELSIF SensorX = FALSE AND SensorY = TRUE THEN
     Diverter := RIGHT;
   ELSE
     Diverter := CENTER;
   END_IF;

   uses AND to check both sensors exactly as required.

2. Step 2: Verify ELSEIF and ELSE branches

   IF SensorX = TRUE AND SensorY = FALSE THEN
     Diverter := LEFT;
   ELSIF SensorX = FALSE AND SensorY = TRUE THEN
     Diverter := RIGHT;
   ELSE
     Diverter := CENTER;
   END_IF;

   correctly uses ELSIF for second condition and ELSE for default.

3. Step 3: Check other options for errors

   IF SensorX = TRUE OR SensorY = FALSE THEN
     Diverter := LEFT;
   ELSEIF SensorX = FALSE OR SensorY = TRUE THEN
     Diverter := RIGHT;
   ELSE
     Diverter := CENTER;
   END_IF;

   uses OR incorrectly, C uses CASE but syntax is not standard PLC, D misses combined conditions.

4. Final Answer:

   The code snippet with AND conditions -> Option B

5. Quick Check:

   Correct AND conditions and ELSIF = A [OK]

Hint: Use AND for combined sensor checks, ELSIF for second condition [OK]

Common Mistakes:

• Using OR instead of AND for combined conditions
• Incorrect CASE syntax in PLC
• Missing combined sensor checks