Level control system in PLC Programming - Mini Project: Build & Apply

Level control system

📖 Scenario: You are working with a water tank that needs to maintain its water level between certain limits. The tank has sensors that detect the current water level. Your task is to create a simple program that reads the water level and controls a pump to fill the tank when the level is low and stop the pump when the level is high.

🎯 Goal: Build a level control system that reads the water level from a sensor, compares it with set thresholds, and controls a pump accordingly.

📋 What You'll Learn

Create a variable to store the current water level.

Create variables for low and high level thresholds.

Write logic to turn the pump ON when the water level is below the low threshold.

Write logic to turn the pump OFF when the water level is above the high threshold.

Display the pump status.

💡 Why This Matters

🌍 Real World

Level control systems are used in water tanks, chemical tanks, and many industrial processes to maintain safe and efficient operation.

💼 Career

Understanding basic control logic and sensor integration is essential for automation engineers and technicians working with PLCs and industrial control systems.

1

Create water level variable

Create a variable called water_level and set it to 50 to represent the current water level.

PLC Programming

# Create a variable called water_level and set it to 50
# Your code here

Hint

Use a simple assignment statement like water_level = 50.

2

Set level thresholds

Create two variables called low_level and high_level. Set low_level to 30 and high_level to 70.

PLC Programming

water_level = 50
# Create variables low_level = 30 and high_level = 70
# Your code here

Hint

Use two assignment statements: low_level = 30 and high_level = 70.

3

Write pump control logic

Create a variable called pump_on. Use an if statement to set pump_on = True if water_level is less than low_level. Use elif to set pump_on = False if water_level is greater than high_level. Otherwise, keep pump_on unchanged and initialize it to False before the conditions.

PLC Programming

water_level = 50
low_level = 30
high_level = 70
# Initialize pump_on to False
# Use if and elif to control pump_on based on water_level
# Your code here

Hint

Start with pump_on = False. Then use if water_level < low_level to set pump_on = True. Use elif water_level > high_level to set pump_on = False.

4

Display pump status

Write a print statement to display "Pump is ON" if pump_on is True, otherwise display "Pump is OFF".

PLC Programming

water_level = 50
low_level = 30
high_level = 70
pump_on = False
if water_level  high_level:
    pump_on = False
# Print "Pump is ON" if pump_on is True, else print "Pump is OFF"
# Your code here

Hint

Use if pump_on: to print "Pump is ON", else print "Pump is OFF".

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