Start-stop motor control in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

PLC Programming

IF StartButton = [1] THEN
    Motor := TRUE;
END_IF;

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

ATRUE

BON

CFALSE

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using FALSE instead of TRUE to detect button press.

Using numeric values like 1 instead of TRUE.

The motor should start when the StartButton is TRUE (pressed).

2fill in blank

medium

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

PLC Programming

IF StopButton = [1] THEN
    Motor := FALSE;
END_IF;

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

AFALSE

BTRUE

COFF

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using FALSE instead of TRUE to detect button press.

Using numeric values like 0 instead of TRUE.

The motor should stop when the StopButton is TRUE (pressed).

3fill in blank

hard

Fix the error in the code to keep the motor running after the start button is released.

PLC Programming

IF StartButton = TRUE THEN
    Motor := TRUE;
ELSIF StopButton = [1] THEN
    Motor := FALSE;
END_IF;

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

AON

BFALSE

C0

DTRUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using FALSE instead of TRUE for stop button condition.

Using numeric values instead of TRUE.

The motor should stop only when the StopButton is TRUE (pressed).

4fill in blank

hard

Fill both blanks to create a latch that keeps the motor running after start is pressed and stops on stop press.

PLC Programming

IF StartButton = [1] THEN
    Motor := TRUE;
ELSIF StopButton = [2] THEN
    Motor := FALSE;
END_IF;

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

ATRUE

BFALSE

CON

DOFF

Attempts:

3 left

💡 Hint

Common Mistakes

Using FALSE for stop button condition.

Using ON/OFF instead of TRUE/FALSE.

Both start and stop buttons are checked for TRUE to control motor state.

5fill in blank

hard

Fill all three blanks to implement a start-stop motor control with a holding contact.

PLC Programming

IF StartButton = [1] OR Motor = [2] THEN
    Motor := TRUE;
END_IF;
IF StopButton = [3] THEN
    Motor := FALSE;
END_IF;

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

ATRUE

DFALSE

Attempts:

3 left

💡 Hint

Common Mistakes

Using FALSE for StartButton or Motor conditions.

Using FALSE for StopButton condition instead of TRUE.

StartButton and Motor are checked for TRUE to keep motor running; StopButton TRUE stops motor.

Practice

1. What is the main purpose of a start-stop motor control circuit in PLC programming?

easy

A. To reverse the motor direction when the Stop button is pressed

B. To run a motor only while the Start button is held down

C. To turn a motor on with a Start button and keep it running until a Stop button is pressed

D. To stop a motor automatically after a set time

Solution

1. Step 1: Understand start-stop control basics

   Start-stop control uses two buttons: Start to turn on the motor, Stop to turn it off.

2. Step 2: Identify motor running behavior

   The motor stays on after Start is pressed and released, until Stop is pressed.

3. Final Answer:

   To turn a motor on with a Start button and keep it running until a Stop button is pressed -> Option C

4. Quick Check:

   Start keeps motor running until Stop pressed = D [OK]

Hint: Motor runs after Start pressed, stops only when Stop pressed [OK]

Common Mistakes:

• Thinking motor runs only while Start is held
• Assuming motor stops automatically without Stop button
• Confusing Stop button with reversing motor

2. Which of the following is the correct ladder logic symbol for a normally open (NO) Start pushbutton in a start-stop motor control?

easy

A. A contact that closes when the button is pressed

B. A contact that stays closed all the time

C. A contact that opens when the button is pressed

D. A coil that energizes the motor

Solution

1. Step 1: Recall NO contact behavior

   A normally open (NO) contact is open by default and closes when pressed.

2. Step 2: Match to Start button function

   The Start button is NO so it closes circuit when pressed to start motor.

3. Final Answer:

   A contact that closes when the button is pressed -> Option A

4. Quick Check:

   NO contact closes on press = B [OK]

Hint: Start button uses NO contact that closes on press [OK]

Common Mistakes:

• Confusing NO with NC (normally closed)
• Thinking Start button contact is always closed
• Mixing coil symbol with contact symbol

3. Given this PLC ladder logic snippet for start-stop control:

Start NO ---[ ]---+---( ) Motor
Stop NC ----[ ]---|
Motor ---[ ]-------+

What happens when the Start button is pressed and then released, assuming the motor was off initially?

medium

A. Motor turns on and stays on until Stop is pressed

B. Motor turns on only while Start is pressed

C. Motor never turns on

D. Motor turns on and off repeatedly

Solution

1. Step 1: Analyze Start button effect

   Pressing Start closes NO contact, energizing Motor coil.

2. Step 2: Understand holding circuit

   Motor contact in parallel holds coil energized after Start released.

3. Final Answer:

   Motor turns on and stays on until Stop is pressed -> Option A

4. Quick Check:

   Holding circuit keeps motor on after Start release = A [OK]

Hint: Holding contact keeps motor on after Start release [OK]

Common Mistakes:

• Thinking motor turns off immediately after Start release
• Ignoring Stop button effect
• Misreading holding contact function

4. In a start-stop motor control program, the motor never turns off when the Stop button is pressed. What is the most likely error?

medium

A. Motor coil is missing from the circuit

B. Start button contact is wired as normally closed (NC)

C. Holding contact is missing from the circuit

D. Stop button contact is wired as normally open (NO) instead of normally closed (NC)

Solution

1. Step 1: Check Stop button wiring

   Stop button must be NC to break circuit when pressed.

2. Step 2: Identify effect of NO Stop button

   If Stop is NO, pressing it does not open circuit, so motor stays on.

3. Final Answer:

   Stop button contact is wired as normally open (NO) instead of normally closed (NC) -> Option D

4. Quick Check:

   Stop must be NC to stop motor = C [OK]

Hint: Stop button must be NC to break motor circuit [OK]

Common Mistakes:

• Wiring Stop as NO contact
• Confusing Start and Stop button contacts
• Forgetting holding contact role

5. You want to add an emergency stop (E-Stop) button to a start-stop motor control circuit that immediately stops the motor when pressed. Which is the best way to add it?

hard

A. Add the E-Stop as a normally open (NO) contact in parallel with the Start button

B. Add the E-Stop as a normally closed (NC) contact in series with the Stop button

C. Add the E-Stop as a coil that energizes the motor

D. Add the E-Stop as a normally open (NO) contact in series with the motor coil

Solution

1. Step 1: Understand emergency stop function

   E-Stop must break power immediately to stop motor safely.

2. Step 2: Choose wiring method

   Placing E-Stop as NC contact in series with Stop button breaks circuit when pressed.

3. Final Answer:

   Add the E-Stop as a normally closed (NC) contact in series with the Stop button -> Option B

4. Quick Check:

   E-Stop NC in series cuts motor power = A [OK]

Hint: E-Stop wired NC in series to cut motor power immediately [OK]

Common Mistakes:

• Wiring E-Stop as NO contact
• Placing E-Stop in parallel with Start button
• Using E-Stop as coil instead of contact