Normally open (NO) contact in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to represent a normally open (NO) contact in ladder logic.

PLC Programming

LD [1]

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

AXIC

BXIO

COTE

DOTL

Attempts:

3 left

💡 Hint

Common Mistakes

Using XIO instead of XIC, which is normally closed (NC) contact.

Using OTE or OTL which are output instructions, not contacts.

The XIC instruction represents a normally open (NO) contact in ladder logic. It passes power when the input is ON.

2fill in blank

medium

Complete the code to turn ON an output coil when the NO contact is closed.

PLC Programming

LD XIC Input1
[1] Output1

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

AXIC

BOTE

CXIO

DOTU

Attempts:

3 left

💡 Hint

Common Mistakes

Using XIC or XIO which are contact instructions, not outputs.

Using OTU which is used to turn off outputs.

The OTE instruction energizes an output coil when the rung conditions are true.

3fill in blank

hard

Fix the error in the code to correctly represent a normally open contact controlling an output.

PLC Programming

LD [1] Input1
OTE Output1

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

AXIC

BXIO

COTE

DOTL

Attempts:

3 left

💡 Hint

Common Mistakes

Using XIO instead of XIC for normally open contact.

Using output instructions in place of contact instructions.

The normally open contact is represented by XIC. Using XIO would represent a normally closed contact, which is incorrect here.

4fill in blank

hard

Fill both blanks to create a rung that uses a normally open contact and an output coil.

PLC Programming

LD [1] StartButton
[2] Motor

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

AXIC

BXIO

COTE

DOTU

Attempts:

3 left

💡 Hint

Common Mistakes

Using XIO for normally open contact.

Using OTU instead of OTE for output coil.

The normally open contact is XIC and the output coil is OTE.

5fill in blank

hard

Fill all three blanks to create a rung that uses a normally open contact, a normally closed contact, and an output coil.

PLC Programming

LD [1] Start
AND [2] Stop
[3] Pump

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

AXIC

BXIO

COTE

DOTL

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up XIC and XIO for contacts.

Using OTL instead of OTE for output coil.

XIC is the normally open contact for Start, XIO is the normally closed contact for Stop, and OTE energizes the Pump output coil.

Practice

1. What does a Normally Open (NO) contact do in a PLC circuit?

easy

A. It remains open until activated, then closes to allow current flow.

B. It remains closed until activated, then opens to stop current flow.

C. It always stays closed regardless of activation.

D. It always stays open regardless of activation.

Solution

1. Step 1: Understand NO contact default state

   A Normally Open contact is open by default, meaning no current flows through it initially.

2. Step 2: Behavior when activated

   When the NO contact is activated (e.g., button pressed), it closes, allowing current to flow.

3. Final Answer:

   It remains open until activated, then closes to allow current flow. -> Option A

4. Quick Check:

   NO contact = open by default, closes when activated [OK]

Hint: NO means open until pressed, then closes [OK]

Common Mistakes:

• Confusing NO with Normally Closed (NC) contact
• Thinking NO contact is closed by default
• Assuming NO contact always stays open

2. Which of the following is the correct syntax to represent a Normally Open (NO) contact in a PLC ladder logic program?

easy

A. --[/]-- symbol

B. |/| symbol

C. | | symbol

D. --[ ]-- symbol

Solution

1. Step 1: Identify NO contact symbol

   The Normally Open contact is represented by two parallel vertical lines: | |.

2. Step 2: Differentiate from NC contact

   The Normally Closed contact uses |/| or --[/]-- symbols, which are different.

3. Final Answer:

   | | symbol -> Option C

4. Quick Check:

   NO contact = | | [OK]

Hint: NO contact looks like two parallel lines | | [OK]

Common Mistakes:

• Using NC contact symbol for NO contact
• Confusing ladder logic symbols
• Mixing up contact and coil symbols

3. Given the following ladder logic snippet with a Normally Open (NO) contact named Start_Button controlling a coil Motor, what happens when Start_Button is pressed?

--| |--( )--
  Start_Button  Motor

medium

A. Motor coil de-energizes, turning the motor OFF.

B. Motor coil energizes, turning the motor ON.

C. Nothing happens; the motor state remains unchanged.

D. Motor coil toggles ON and OFF rapidly.

Solution

1. Step 1: Analyze NO contact behavior when pressed

   Pressing the Start_Button closes the NO contact, allowing current to flow.

2. Step 2: Effect on coil Motor

   Current energizes the Motor coil, turning the motor ON.

3. Final Answer:

   Motor coil energizes, turning the motor ON. -> Option B

4. Quick Check:

   NO contact pressed = coil energized [OK]

Hint: Pressing NO contact energizes coil [OK]

Common Mistakes:

• Assuming coil de-energizes when NO contact closes
• Thinking NO contact does not affect coil
• Confusing coil with contact behavior

4. In the ladder logic below, the Normally Open (NO) contact Sensor is supposed to start the Conveyor motor. However, the motor never starts even when the sensor is triggered. What is the likely error?

--|/|--( )--
 Sensor Conveyor

medium

A. The contact is Normally Closed (NC) instead of Normally Open (NO).

B. The coil Conveyor is wired incorrectly.

C. The sensor is not physically connected.

D. The power supply is off.

Solution

1. Step 1: Identify contact type in code

   The contact symbol |/| represents a Normally Closed (NC) contact, not Normally Open (NO).

2. Step 2: Effect of NC contact on motor start

   Since the sensor is triggered (activated), the NC contact opens, breaking the circuit and preventing the motor from starting.

3. Final Answer:

   The contact is Normally Closed (NC) instead of Normally Open (NO). -> Option A

4. Quick Check:

   Wrong contact type = motor won't start [OK]

Hint: Check contact symbol: |/| means NC, not NO [OK]

Common Mistakes:

• Confusing NC and NO contact symbols
• Assuming coil wiring is always the issue
• Ignoring sensor physical connection

5. You want to design a control circuit where a Normally Open (NO) start button must be pressed to start a machine. Which logic setup correctly uses the NO contact to achieve this?

hard

A. Use the NO contact in series with the motor coil; pressing the button breaks the circuit to start the machine.

B. Use the NO contact in parallel with the motor coil; pressing the button breaks the circuit to start the machine.

C. Use the NO contact in parallel with the motor coil; pressing the button energizes the coil to start the machine.

D. Use the NO contact in series with the motor coil; pressing the button energizes the coil to start the machine.

Solution

1. Step 1: Understand NO contact behavior in start circuit

   A Normally Open start button is open by default, meaning no current flows through it initially (machine OFF).

2. Step 2: Effect of pressing NO start button

   When the NO button is pressed, it closes, allowing current to flow and energizing the motor coil to start the machine.

3. Final Answer:

   Use the NO contact in series with the motor coil; pressing the button energizes the coil to start the machine. -> Option D

4. Quick Check:

   NO series press = coil energized to start [OK]

Hint: NO start button in series energizes coil when pressed [OK]

Common Mistakes:

• Placing NO contact in parallel for start function
• Assuming pressing NO button breaks circuit to start
• Confusing NO and NC contacts in control circuits