Indicator light control in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to turn on the indicator light when the start button is pressed.

PLC Programming

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

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

A0

BFALSE

CTRUE

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of 1 to check if the button is pressed.

Using FALSE instead of TRUE.

The start button is pressed when its value is 1 (TRUE). So the condition should check if StartButton equals 1.

2fill in blank

medium

Complete the code to turn off the indicator light when the stop button is pressed.

PLC Programming

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

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

AFALSE

B0

C1

DTRUE

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 0 instead of 1.

Assigning TRUE instead of FALSE to IndicatorLight.

The stop button is pressed when its value is 1 (TRUE). So the condition should check if StopButton equals 1.

3fill in blank

hard

Fix the error in the code to correctly toggle the indicator light when the toggle button is pressed.

PLC Programming

IF ToggleButton = [1] THEN
    IndicatorLight := NOT IndicatorLight;
END_IF;

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

A1

B0

CFALSE

DTRUE

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 0 instead of 1.

Using FALSE instead of TRUE.

The toggle button is pressed when its value is 1 (TRUE). The condition must check for 1 to toggle the light.

4fill in blank

hard

Fill both blanks to turn on the indicator light only when the start button is pressed and the safety switch is ON.

PLC Programming

IF StartButton = [1] AND SafetySwitch = [2] THEN
    IndicatorLight := TRUE;
END_IF;

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

A1

B0

CTRUE

DFALSE

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or FALSE for pressed or ON states.

Using OR instead of AND.

The start button is pressed when it equals 1, and the safety switch is ON when TRUE. Both conditions must be true to turn on the light.

5fill in blank

hard

Fill all three blanks to turn off the indicator light when the stop button is pressed or the emergency stop is activated.

PLC Programming

IF StopButton = [1] OR EmergencyStop = [2] THEN
    IndicatorLight := [3];
END_IF;

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

A1

BTRUE

CFALSE

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or FALSE for pressed or activated states incorrectly.

Assigning TRUE instead of FALSE to IndicatorLight.

Stop button pressed means 1, emergency stop activated means TRUE, and to turn off the light we assign FALSE.

Practice

1. What is the main purpose of an indicator light in a PLC-controlled machine?

easy

A. To increase the machine's speed

B. To show the status of the machine or process clearly

C. To store data from the machine

D. To control the temperature of the machine

Solution

1. Step 1: Understand indicator light function

   Indicator lights are used to show if a machine is running, stopped, or has a fault.

2. Step 2: Match purpose to options

   Only To show the status of the machine or process clearly describes showing status clearly, which is the main purpose.

3. Final Answer:

   To show the status of the machine or process clearly -> Option B

4. Quick Check:

   Indicator lights = show status [OK]

Hint: Indicator lights always show machine status visually [OK]

Common Mistakes:

• Thinking indicator lights control machine speed
• Confusing indicator lights with data storage
• Assuming indicator lights control temperature

2. Which of the following is the correct syntax to turn ON an indicator light named Light1 when a condition StartButton is TRUE in a PLC program?

easy

A. IF StartButton THEN Light1 = ON;

B. IF (StartButton) Light1 = ON;

C. IF StartButton Light1 = ON;

D. IF StartButton THEN Light1 ON;

Solution

1. Step 1: Identify correct IF syntax in PLC

   Standard PLC IF syntax uses 'IF condition THEN action;' format.

2. Step 2: Check each option

   IF StartButton THEN Light1 = ON; matches correct syntax with 'IF StartButton THEN Light1 = ON;'. Others miss THEN or equal sign.

3. Final Answer:

   IF StartButton THEN Light1 = ON; -> Option A

4. Quick Check:

   IF ... THEN ... = ...; syntax [OK]

Hint: Always use THEN and = in PLC IF statements [OK]

Common Mistakes:

• Omitting THEN keyword
• Missing equal sign for assignment
• Incorrect parentheses usage

3. Given this PLC code snippet:

IF Sensor = TRUE THEN
  LightGreen = ON;
ELSE
  LightGreen = OFF;
END_IF;

What will be the state of LightGreen if Sensor is FALSE?

medium

A. LightGreen will be ON

B. LightGreen will blink

C. LightGreen state will not change

D. LightGreen will be OFF

Solution

1. Step 1: Analyze IF condition with Sensor FALSE

   Since Sensor = FALSE, the ELSE branch runs.

2. Step 2: Determine LightGreen state in ELSE branch

   ELSE sets LightGreen = OFF, so light turns off.

3. Final Answer:

   LightGreen will be OFF -> Option D

4. Quick Check:

   Sensor FALSE -> ELSE -> LightGreen OFF [OK]

Hint: FALSE condition triggers ELSE branch [OK]

Common Mistakes:

• Assuming light stays ON when sensor is FALSE
• Thinking light blinks automatically
• Ignoring ELSE branch

4. Identify the error in this PLC code controlling an indicator light:

IF Start = TRUE THEN
  LightRed = ON
ELSE
  LightRed = OFF;
END_IF;

medium

A. Wrong variable name 'Start'

B. Incorrect use of ELSE keyword

C. Missing semicolon after 'LightRed = ON'

D. Missing END_IF statement

Solution

1. Step 1: Check statement endings

   PLC statements require semicolons at end; 'LightRed = ON' lacks semicolon.

2. Step 2: Verify other syntax parts

   ELSE and END_IF are correctly used; variable name 'Start' is valid.

3. Final Answer:

   Missing semicolon after 'LightRed = ON' -> Option C

4. Quick Check:

   Every statement ends with ; [OK]

Hint: Check every statement ends with a semicolon [OK]

Common Mistakes:

• Forgetting semicolons
• Misusing ELSE keyword
• Assuming END_IF is optional

5. You want to control two indicator lights: LightGreen turns ON when MachineRunning is TRUE, and LightRed turns ON when MachineFault is TRUE. Which PLC code correctly implements this logic?

hard

A. IF MachineRunning THEN LightGreen = ON; ELSE LightGreen = OFF; END_IF;\nIF MachineFault THEN LightRed = ON; ELSE LightRed = OFF; END_IF;

B. IF MachineRunning = TRUE AND MachineFault = FALSE THEN LightGreen = ON; ELSE LightGreen = OFF; END_IF;

C. IF MachineRunning THEN LightGreen = ON; IF MachineFault THEN LightRed = ON; END_IF;

D. IF MachineRunning OR MachineFault THEN LightGreen = ON; ELSE LightRed = ON; END_IF;

Solution

1. Step 1: Understand requirements for each light

   LightGreen depends only on MachineRunning; LightRed depends only on MachineFault.

2. Step 2: Check each option for correct separate control

   IF MachineRunning THEN LightGreen = ON; ELSE LightGreen = OFF; END_IF;\nIF MachineFault THEN LightRed = ON; ELSE LightRed = OFF; END_IF; uses two separate IF blocks, correctly controlling each light independently.

3. Step 3: Identify errors in other options

   IF MachineRunning = TRUE AND MachineFault = FALSE THEN LightGreen = ON; ELSE LightGreen = OFF; END_IF; combines conditions incorrectly; IF MachineRunning THEN LightGreen = ON; IF MachineFault THEN LightRed = ON; END_IF; misses ELSE for LightRed OFF; IF MachineRunning OR MachineFault THEN LightGreen = ON; ELSE LightRed = ON; END_IF; mixes logic wrongly.

4. Final Answer:

   Separate IF blocks for each light with proper ON/OFF control -> Option A

5. Quick Check:

   Separate IFs for independent lights [OK]

Hint: Control each light with its own IF-ELSE block [OK]

Common Mistakes:

• Combining conditions incorrectly
• Missing ELSE to turn lights OFF
• Using OR instead of separate controls