Level control system in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the pump when the level is low.

PLC Programming

IF level_sensor = [1] THEN
    pump := TRUE;
END_IF;

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

ALOW

BOFF

CON

DHIGH

Attempts:

3 left

💡 Hint

Common Mistakes

Using HIGH instead of LOW to start the pump.

Confusing pump ON/OFF with sensor states.

The pump should start when the level sensor reads LOW, indicating the tank is empty or below the threshold.

2fill in blank

medium

Complete the code to stop the pump when the level is high.

PLC Programming

IF level_sensor = [1] THEN
    pump := FALSE;
END_IF;

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

ALOW

BHIGH

CON

DOFF

Attempts:

3 left

💡 Hint

Common Mistakes

Stopping the pump when the level is LOW instead of HIGH.

Mixing sensor states with pump states.

The pump should stop when the level sensor reads HIGH, meaning the tank is full.

3fill in blank

hard

Fix the error in the code to correctly check the level sensor and control the pump.

PLC Programming

IF level_sensor [1] HIGH THEN
    pump := FALSE;
ELSE
    pump := TRUE;
END_IF;

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

A!=

B=

C<>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '==' for comparison.

Using '!=' or '<>' which may not be supported in this context.

In PLC programming, '=' is used for assignment, '==' is used to compare values for equality.

4fill in blank

hard

Fill both blanks to create a condition that starts the pump only when the level is low and the emergency stop is not active.

PLC Programming

IF level_sensor = [1] AND emergency_stop = [2] THEN
    pump := TRUE;
END_IF;

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

ALOW

BTRUE

CFALSE

DHIGH

Attempts:

3 left

💡 Hint

Common Mistakes

Using HIGH instead of LOW for level_sensor.

Using TRUE for emergency_stop which means the stop is active.

The pump starts when the level is LOW and emergency_stop is FALSE (not active).

5fill in blank

hard

Fill all three blanks to create a dictionary mapping sensor names to their states, filtering only sensors that are active (TRUE).

PLC Programming

active_sensors = { [1]: [2] for [1] in sensors if sensors[[1]] == TRUE }

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

Asensor

Bsensors[sensor]

Dstate

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not filtering sensors that are TRUE.

We use 'sensor' as the loop variable and key, 'sensors[sensor]' as the value, and filter where sensors[sensor] is TRUE.

Practice

1. What is the main purpose of a level control system in a tank?

easy

A. To measure the temperature of the liquid

B. To keep the liquid level within safe limits automatically

C. To change the color of the liquid

D. To increase the pressure inside the tank

Solution

1. Step 1: Understand the system goal

   A level control system is designed to maintain liquid levels safely.

2. Step 2: Identify the correct function

   It uses sensors and pumps to keep levels steady, not temperature or color.

3. Final Answer:

   To keep the liquid level within safe limits automatically -> Option B

4. Quick Check:

   Level control = safe liquid level [OK]

Hint: Focus on what 'level control' means in real life [OK]

Common Mistakes:

• Confusing level control with temperature control
• Thinking it changes liquid properties
• Assuming it controls pressure

2. Which of the following is the correct simple IF statement to turn ON a pump when the level is below 30%?

easy

A. IF level = 30 THEN pump = OFF;

B. IF level > 30 THEN pump = ON;

C. IF level < 30 THEN pump = ON;

D. IF level <= 30 THEN pump = OFF;

Solution

1. Step 1: Understand the condition for turning pump ON

   The pump should turn ON when level is below 30% to fill the tank.

2. Step 2: Match the correct syntax

   IF level < 30 THEN pump = ON; correctly uses IF level < 30 THEN pump = ON;

3. Final Answer:

   IF level < 30 THEN pump = ON; -> Option C

4. Quick Check:

   Turn ON pump if level less than 30% [OK]

Hint: Pump ON when level is less, so use '<' operator [OK]

Common Mistakes:

• Using > instead of < for turning pump ON
• Confusing ON and OFF states
• Using equality instead of inequality

3. Given this PLC logic snippet:

IF level < 40 THEN pump = ON;
ELSE pump = OFF;

What will be the pump state if the level sensor reads 45?

medium

A. Pump will be ON

B. Pump will stay in previous state

C. Pump state will toggle rapidly

D. Pump will be OFF

Solution

1. Step 1: Check the condition with level = 45

   Since 45 is not less than 40, the IF condition is false.

2. Step 2: Follow the ELSE branch

   Because IF is false, pump = OFF is executed.

3. Final Answer:

   Pump will be OFF -> Option D

4. Quick Check:

   Level 45 ≥ 40 means pump OFF [OK]

Hint: Check IF condition with given value carefully [OK]

Common Mistakes:

• Assuming pump stays ON without checking ELSE
• Confusing < and > operators
• Ignoring ELSE branch

4. Identify the error in this PLC code snippet for level control:

IF level > 70 THEN pump = ON;
ELSE pump = ON;

medium

A. Pump is always ON regardless of level

B. Syntax error: missing ENDIF

C. Pump never turns ON

D. Level sensor value is not checked

Solution

1. Step 1: Analyze the IF and ELSE assignments

   Both IF and ELSE branches set pump = ON, so pump is always ON.

2. Step 2: Understand the logic flaw

   This means pump never turns OFF, ignoring level changes.

3. Final Answer:

   Pump is always ON regardless of level -> Option A

4. Quick Check:

   Same action in IF and ELSE means no control [OK]

Hint: Check if IF and ELSE do different things [OK]

Common Mistakes:

• Thinking ELSE is missing
• Assuming pump turns OFF somewhere
• Ignoring logic duplication

5. You want to design a level control system that turns ON the pump when level is below 30%, turns OFF when above 70%, and keeps the pump state unchanged between 30% and 70%. Which logic correctly implements this?

hard

A. IF level < 30 THEN pump = ON; ELSE IF level > 70 THEN pump = OFF;

B. IF level <= 70 THEN pump = OFF; ELSE pump = ON;

C. IF level < 30 THEN pump = ON; ELSE pump = OFF;

D. IF level > 70 THEN pump = ON; ELSE IF level < 30 THEN pump = OFF;

Solution

1. Step 1: Understand the required behavior

   Turn pump ON below 30%, OFF above 70%, and keep state unchanged between 30% and 70%.

2. Step 2: Analyze each option

   IF level < 30 THEN pump = ON; ELSE IF level > 70 THEN pump = OFF; turns ON if level < 30, OFF if level > 70, and does nothing in between (keeps state).

3. Final Answer:

   IF level < 30 THEN pump = ON; ELSE IF level > 70 THEN pump = OFF; -> Option A

4. Quick Check:

   Two conditions control pump ON/OFF, else no change [OK]

Hint: Use two IFs for ON and OFF, no ELSE for unchanged [OK]

Common Mistakes:

• Turning pump OFF immediately below 70%
• Not handling the middle range correctly
• Reversing ON and OFF conditions