Conveyor sorting system in PLC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Conveyor Motor Control Logic

Given the following PLC ladder logic snippet controlling a conveyor motor, what will be the motor state if the start button is pressed and the emergency stop is not activated?

PLC Programming

Start_Button = TRUE
Emergency_Stop = FALSE
Motor_Running = Start_Button AND NOT Emergency_Stop

A Motor_Running = UNKNOWN

B Motor_Running = FALSE

C Motor_Running = ERROR

D Motor_Running = TRUE

💡 Hint

Think about how the AND and NOT operators work with TRUE and FALSE inputs.

The motor runs only if the start button is pressed (TRUE) and the emergency stop is not active (FALSE). So Motor_Running = TRUE AND NOT FALSE = TRUE.

📝 Syntax

intermediate

Identify the Syntax Error in Conveyor Sensor Code

Which option contains a syntax error in this PLC structured text code snippet for reading a conveyor sensor?

PLC Programming

IF SensorInput = TRUE THEN
  ConveyorStatus := "Running";
ELSE
  ConveyorStatus := "Stopped";
END_IF

A

IF SensorInput == TRUE THEN
  ConveyorStatus := "Running";
ELSE
  ConveyorStatus := "Stopped";
END_IF

B

IF SensorInput THEN
  ConveyorStatus := "Running";
ELSE
  ConveyorStatus := "Stopped";
END_IF

C

IF SensorInput = TRUE THEN
  ConveyorStatus := "Running";
ELSE
  ConveyorStatus := "Stopped";
END_IF

D

FI_DNE
;"deppotS" =: sutatSroyevnoC  
ESLE
;"gninnuR" =: sutatSroyevnoC  
NEHT EURT = tupnIrosneS FI

💡 Hint

Check the equality operator used in PLC structured text.

In PLC structured text, '=' is used for comparison, not '=='. Using '==' causes a syntax error.

🔧 Debug

advanced

Debug Conveyor Diverter Logic

The conveyor diverter should activate when the item color sensor detects red. The code below does not activate the diverter. What is the cause?

PLC Programming

IF ColorSensor = "Red" THEN
  Diverter := TRUE
ELSE
  Diverter := FALSE
END_IF

A Missing semicolons at the end of assignment lines cause syntax errors.

B The variable Diverter is not declared as a BOOL, causing a type error.

C The string comparison uses single quotes instead of double quotes, causing a mismatch.

D The IF statement lacks parentheses around the condition.

💡 Hint

Check the syntax rules for statements in PLC structured text.

In PLC structured text, each statement must end with a semicolon. Missing semicolons cause syntax errors preventing code execution.

🚀 Application

advanced

Calculate Items Sorted Per Minute

A conveyor system sorts items at a rate controlled by a timer. The timer triggers every 2 seconds to activate the sorter. How many items are sorted in 1 minute?

A 60 items

B 30 items

C 120 items

D 15 items

💡 Hint

Divide 60 seconds by the timer interval to find the number of triggers per minute.

60 seconds / 2 seconds per trigger = 30 triggers per minute, so 30 items sorted.

🧠 Conceptual

expert

Effect of Sensor Delay on Sorting Accuracy

If a conveyor sensor has a delay of 0.5 seconds before detecting an item, and the conveyor speed is 1 meter per second, what is the minimum distance required between items to ensure accurate sorting?

A 0.5 meters

B 0.25 meters

C 1 meter

D 2 meters

💡 Hint

Multiply the sensor delay by the conveyor speed to get the delay distance, then double it to avoid overlap.

Distance = speed × delay = 1 m/s × 0.5 s = 0.5 meters. To avoid overlap, spacing must be at least double that, so 1 meter.

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