Forward-reverse motor control with interlock in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the motor in forward direction when the forward button is pressed.

PLC Programming

IF Forward_Button = 1 THEN Motor_Forward := [1] END_IF

Drag options to blanks, or click blank then click option'

ATRUE

BFALSE

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using FALSE or 0 which do not start the motor.

Using numeric 1 instead of TRUE in some PLC languages.

Setting Motor_Forward to TRUE starts the motor in forward direction when the forward button is pressed.

2fill in blank

medium

Complete the code to stop the motor when the stop button is pressed.

PLC Programming

IF Stop_Button = 1 THEN Motor_Forward := [1]; Motor_Reverse := [1] END_IF

Drag options to blanks, or click blank then click option'

A0

BTRUE

C1

DFALSE

Attempts:

3 left

💡 Hint

Common Mistakes

Setting outputs to TRUE which keeps the motor running.

Using numeric 1 instead of FALSE to stop.

Setting both Motor_Forward and Motor_Reverse to FALSE stops the motor when the stop button is pressed.

3fill in blank

hard

Fix the error in the interlock logic to prevent both forward and reverse from being ON at the same time.

PLC Programming

IF Forward_Button = 1 AND Motor_Reverse = [1] THEN Motor_Forward := TRUE END_IF

Drag options to blanks, or click blank then click option'

ATRUE

BFALSE

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if Motor_Reverse is TRUE which allows both directions ON.

Using numeric 1 instead of FALSE.

The interlock requires Motor_Reverse to be FALSE before Motor_Forward can be TRUE, preventing both directions ON simultaneously.

4fill in blank

hard

Fill both blanks to complete the interlock logic preventing simultaneous forward and reverse motor operation.

PLC Programming

IF Forward_Button = 1 AND Motor_Reverse = [1] THEN Motor_Forward := TRUE END_IF
IF Reverse_Button = 1 AND Motor_Forward = [2] THEN Motor_Reverse := TRUE END_IF

Drag options to blanks, or click blank then click option'

AFALSE

BTRUE

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using TRUE or 1 which allows both directions ON.

Mixing numeric and boolean values inconsistently.

Both conditions check that the opposite motor direction is OFF (FALSE) before turning ON the requested direction, ensuring interlock.

5fill in blank

hard

Fill all three blanks to complete the full forward-reverse motor control with interlock and stop logic.

PLC Programming

IF Stop_Button = 1 THEN Motor_Forward := [1]; Motor_Reverse := [1] END_IF
IF Forward_Button = 1 AND Motor_Reverse = [2] THEN Motor_Forward := TRUE END_IF
IF Reverse_Button = 1 AND Motor_Forward = [3] THEN Motor_Reverse := TRUE END_IF

Drag options to blanks, or click blank then click option'

AFALSE

BTRUE

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using TRUE or 1 to stop motor outputs.

Allowing both directions ON simultaneously.

Stop sets both directions OFF (FALSE). Forward and Reverse start only if opposite direction is OFF (FALSE), ensuring safe interlock.

Practice

1. What is the main purpose of using an interlock in forward-reverse motor control?

easy

A. To increase the motor speed beyond its rated capacity

B. To prevent the motor from running forward and reverse at the same time

C. To allow the motor to run in both directions simultaneously

D. To reduce the power consumption of the motor

Solution

1. Step 1: Understand interlock function

   An interlock is a safety feature that prevents conflicting commands from activating simultaneously.

2. Step 2: Apply to motor control

   In forward-reverse motor control, the interlock stops both forward and reverse commands from running at the same time to protect the motor.

3. Final Answer:

   To prevent the motor from running forward and reverse at the same time -> Option B

4. Quick Check:

   Interlock prevents simultaneous directions = A [OK]

Hint: Interlock means 'no two directions at once' [OK]

Common Mistakes:

• Thinking interlock increases speed
• Believing motor can run both ways simultaneously
• Confusing interlock with power saving

2. Which of the following is the correct ladder logic condition to implement an interlock for forward and reverse motor control?

easy

A. Forward = StartF AND NOT Reverse

B. Forward = StartF OR Reverse

C. Forward = StartF AND Reverse

D. Forward = NOT StartF AND Reverse

Solution

1. Step 1: Understand interlock logic

   The forward command should only activate if the forward start is pressed and the reverse is NOT active.

2. Step 2: Match logic to options

   Forward = StartF AND NOT Reverse uses AND with NOT Reverse, which correctly prevents forward and reverse running together.

3. Final Answer:

   Forward = StartF AND NOT Reverse -> Option A

4. Quick Check:

   Forward requires StartF and no Reverse = D [OK]

Hint: Use AND with NOT for interlock conditions [OK]

Common Mistakes:

• Using OR instead of AND
• Missing NOT to block reverse
• Allowing both directions simultaneously

3. Given the following PLC code snippet for motor control:

Forward = StartF AND NOT Reverse
Reverse = StartR AND NOT Forward

What will be the state of Forward and Reverse if both StartF and StartR are pressed at the same time?

medium

A. Forward = True, Reverse = False

B. Forward = False, Reverse = True

C. Forward = False, Reverse = False

D. Forward = True, Reverse = True

Solution

1. Step 1: Analyze Forward condition

   Forward = StartF AND NOT Reverse. Since StartR is pressed, Reverse may be True, so NOT Reverse is False, Forward is False.

2. Step 2: Analyze Reverse condition

   Reverse = StartR AND NOT Forward. Forward is False (from step 1), so NOT Forward is True, but Reverse depends on StartR AND True = True. However, this creates a conflict because Forward depends on Reverse and vice versa.

3. Step 3: Resolve conflict

   Because both depend on each other's negation, neither can be True simultaneously. Both will remain False to avoid conflict.

4. Final Answer:

   Forward = False, Reverse = False -> Option C

5. Quick Check:

   Both pressed blocks both directions = C [OK]

Hint: Both starts pressed disables both directions [OK]

Common Mistakes:

• Assuming both directions run simultaneously
• Ignoring mutual exclusion logic
• Forgetting NOT conditions

4. Identify the error in this forward-reverse motor control logic:

Forward = StartF OR NOT Reverse
Reverse = StartR OR NOT Forward

medium

A. Using OR instead of AND causes both directions to run simultaneously

B. Missing NOT operator before StartF and StartR

C. Correct logic with no errors

D. Reverse should depend only on StartF

Solution

1. Step 1: Analyze use of OR operator

   Using OR means Forward can be True if StartF is True or Reverse is False, which can allow both Forward and Reverse to be True simultaneously.

2. Step 2: Understand interlock requirement

   Interlock requires AND with NOT to prevent simultaneous activation, so OR breaks this rule.

3. Final Answer:

   Using OR instead of AND causes both directions to run simultaneously -> Option A

4. Quick Check:

   OR allows both directions = A [OK]

Hint: Interlock needs AND NOT, not OR [OK]

Common Mistakes:

• Confusing OR with AND
• Ignoring interlock logic
• Assuming logic is correct without testing

5. You want to design a forward-reverse motor control with interlock using a PLC. Which of the following ladder logic snippets correctly implements the interlock to prevent simultaneous forward and reverse commands?

hard

A. Forward = StartF OR Reverse
Reverse = StartR OR Forward

B. Forward = StartF AND StartR
Reverse = StartR AND StartF

C. Forward = StartF AND Reverse
Reverse = StartR AND Forward

D. Forward = StartF AND NOT Reverse
Reverse = StartR AND NOT Forward

Solution

1. Step 1: Understand interlock logic requirements

   Interlock requires that Forward only runs if Reverse is NOT running, and vice versa, to avoid damage.

2. Step 2: Evaluate each option

   Forward = StartF AND NOT Reverse Reverse = StartR AND NOT Forward uses AND with NOT conditions correctly to prevent simultaneous activation. The other options allow both directions or require both starts simultaneously, which is incorrect.

3. Final Answer:

   Forward = StartF AND NOT Reverse Reverse = StartR AND NOT Forward -> Option D

4. Quick Check:

   AND with NOT ensures interlock = B [OK]

Hint: Use AND NOT for safe forward-reverse control [OK]

Common Mistakes:

• Using OR instead of AND
• Allowing both directions at once
• Requiring both start buttons pressed