Operator input screens in PLC Programming - Mini Project: Build & Apply

Operator Input Screens

📖 Scenario: You are programming a simple machine control system. The operator needs to input a target speed and a start command through the operator input screen. Your task is to create a program that reads these inputs and stores them for the machine to use.

🎯 Goal: Build a PLC program that reads an operator's input for target_speed and a start_button signal, then stores these values in variables for the machine control logic.

📋 What You'll Learn

Create variables to hold the operator inputs: target_speed and start_button.

Create a configuration variable max_speed to limit the speed input.

Write logic to read the operator inputs and apply the speed limit.

Output the final target_speed and start_button values.

💡 Why This Matters

🌍 Real World

Operator input screens are used in industrial machines to allow human operators to set parameters like speed and start commands safely and easily.

💼 Career

Understanding how to read and process operator inputs is essential for PLC programmers working in manufacturing automation and control systems.

1

Create operator input variables

Create two variables: target_speed as an integer initialized to 0, and start_button as a boolean initialized to FALSE.

PLC Programming

# Create 'target_speed' and 'start_button' variables
# Your code here

Hint

Use the VAR section to declare variables. Initialize target_speed to 0 and start_button to FALSE.

2

Add maximum speed configuration

Add a constant integer variable called max_speed and set it to 100 to limit the maximum allowed speed.

PLC Programming

VAR
    target_speed : INT := 0;
    start_button : BOOL := FALSE;
    // Add 'max_speed' constant here
# Your code here

Hint

Declare max_speed as an integer variable with value 100 in the VAR section.

3

Read and limit operator inputs

Write logic to read the operator inputs: assign target_speed from InputSpeed and start_button from InputStart. Limit target_speed to not exceed max_speed.

PLC Programming

VAR
    target_speed : INT := 0;
    start_button : BOOL := FALSE;
    max_speed : INT := 100;
END_VAR

// Read inputs and limit speed
// Your code here

Hint

Assign target_speed and start_button from inputs. Use an IF statement to limit target_speed to max_speed.

4

Output the operator input values

Write code to output the final values of target_speed and start_button using Print() statements.

PLC Programming

VAR
    target_speed : INT := 0;
    start_button : BOOL := FALSE;
    max_speed : INT := 100;
    InputSpeed : INT;
    InputStart : BOOL;
END_VAR

// Read inputs
// Limit speed
// Print the final values
# Your code here

Hint

Use Print() to show the values. Convert target_speed and start_button to strings before printing.

Practice

1. What is the main purpose of an operator input screen in PLC programming?

easy

A. To allow users to enter data and control the machine

B. To display error logs only

C. To run the PLC program automatically

D. To store historical data for analysis

Solution

1. Step 1: Understand the role of operator input screens

   Operator input screens are designed for users to interact with the machine by entering commands or data. The main purpose is to allow users to enter data and control the machine.

2. Final Answer:

   To allow users to enter data and control the machine -> Option A

3. Quick Check:

   Operator input screens = user control [OK]

Hint: Think: Who uses the screen and why? [OK]

Common Mistakes:

• Confusing input screens with data storage
• Thinking input screens only display errors
• Assuming input screens run the program automatically

2. Which of the following is the correct syntax to define a numeric input field named SpeedInput in a PLC operator screen?

easy

A. Define SpeedInput as NumericInput

B. NumericInput SpeedInput

C. InputField SpeedInput Numeric

D. SpeedInput = NumericInput()

Solution

1. Step 1: Review common syntax for input fields

   In many PLC screen definitions, input fields are declared with the keyword InputField followed by the name and type, such as InputField SpeedInput Numeric. Other forms use incorrect or unsupported syntax.

2. Final Answer:

   InputField SpeedInput Numeric -> Option C

3. Quick Check:

   InputField + name + type = correct syntax [OK]

Hint: Look for keyword 'InputField' with name and type order [OK]

Common Mistakes:

• Using assignment syntax instead of declaration
• Omitting the InputField keyword
• Mixing up order of name and type

3. Given this snippet of a PLC operator screen script:

InputField Temperature Numeric
Button Submit
DisplayMessage "Enter temperature and press Submit"

What will the operator see when the screen loads?

medium

A. An error because DisplayMessage is not valid

B. Only a Submit button and a message

C. A numeric input box labeled Submit and a Temperature button

D. A numeric input box labeled Temperature, a Submit button, and a message prompting input

Solution

1. Step 1: Analyze each line of the script

   The script defines a numeric input field named Temperature, a button named Submit, and a message "Enter temperature and press Submit". The operator will see the input box for Temperature, the Submit button, and the message prompting input.

2. Final Answer:

   A numeric input box labeled Temperature, a Submit button, and a message prompting input -> Option D

3. Quick Check:

   InputField + Button + DisplayMessage = all visible [OK]

Hint: Match script lines to screen elements shown [OK]

Common Mistakes:

• Ignoring the DisplayMessage line
• Confusing button and input field names
• Assuming syntax errors without checking

4. Identify the error in this operator input screen code snippet:

InputField Speed Numeric
Button Start
DisplayMessage "Set speed and press Start"
InputField Speed Text

medium

A. Speed input field is declared twice with different types

B. Button Start is missing parentheses

C. DisplayMessage should be inside quotes

D. No error, code is correct

Solution

1. Step 1: Review declarations of input fields

   The code declares Speed as a Numeric input field first, then again as a Text input field. Declaring the same input field twice with different types causes conflict and confusion in the screen design.

2. Final Answer:

   Speed input field is declared twice with different types -> Option A

3. Quick Check:

   Duplicate input fields with different types = error [OK]

Hint: Check for repeated names with different types [OK]

Common Mistakes:

• Thinking button syntax is wrong
• Ignoring duplicate input field declarations
• Assuming DisplayMessage syntax error

5. You want to create an operator input screen that asks for two numeric values, Length and Width, and calculates the area when the user presses a Calculate button. Which script snippet correctly sets up the input fields and button to achieve this?

hard

A. InputField Length Numeric
InputField Width Numeric
Button Calculate
OnPress CalculateArea(Length, Width)

B. InputField Length Numeric
InputField Width Numeric
Button Calculate
OnButton Calculate CalculateArea(Length, Width)

C. InputField Length Text
InputField Width Text
Button Calculate
OnButton Calculate CalculateArea(Length, Width)

D. InputField Length Numeric
InputField Width Numeric
Button Calculate
OnClick CalculateArea(Length, Width)

Solution

1. Step 1: Verify input fields and button event syntax

   Length and Width must be Numeric inputs for area calculation; Text inputs are incorrect. The button event requires the standard syntax OnButton Calculate CalculateArea(Length, Width). Event keywords like OnPress or OnClick are not standard.

2. Final Answer:

   InputField Length Numeric InputField Width Numeric Button Calculate OnButton Calculate CalculateArea(Length, Width) -> Option B

3. Quick Check:

   Numeric inputs + OnButton event = correct setup [OK]

Hint: Use numeric inputs and OnButton event for calculations [OK]

Common Mistakes:

• Using Text input for numeric values
• Using wrong event keywords like OnPress or OnClick
• Omitting event handler for button