PLC program documentation standards in PLC Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of PLC program documentation?

The main purpose is to clearly explain how the PLC program works, making it easier for others to understand, maintain, and troubleshoot the system.

beginner

Name three key elements that should be included in PLC program documentation.

1. Description of program functions and logic
2. List and explanation of inputs and outputs
3. Comments on special instructions or sequences

beginner

Why are comments important in PLC programs?

Comments help explain what each part of the program does, making it easier for anyone reading the code to understand the logic without guessing.

intermediate

What standard format is recommended for documenting PLC programs?

A clear, consistent format including a program overview, detailed descriptions of each routine, input/output lists, and revision history is recommended.

intermediate

How does good PLC documentation help during troubleshooting?

It provides quick insight into how the program should behave, helping technicians find and fix problems faster without trial and error.

What should you always include in PLC program comments?

A Explanation of the logic and purpose of code sections

B Personal opinions about the program

C Unrelated notes about other projects

D Only variable names without explanation

Comments should clearly explain the logic and purpose to help others understand the program.

Which of the following is NOT a key part of PLC program documentation?

A Input and output descriptions

B Program revision history

C User's personal contact details

D Program function overview

User's personal contact details are not part of standard PLC program documentation.

Why is a consistent documentation format important?

A It allows skipping some parts of the program

B It reduces the program size

C It hides complex parts of the program

D It makes the documentation easier to read and maintain

Consistency helps users quickly find and understand information.

What is the benefit of documenting inputs and outputs clearly?

A Helps understand how the PLC interacts with the machine

B Makes the program run faster

C Prevents the need for comments

D Allows ignoring hardware details

Clear input/output documentation shows how the program controls and responds to the machine.

When should PLC program documentation be updated?

A Only when the program is first created

B Every time the program is changed

C Once a year regardless of changes

D Never, documentation is static

Documentation should always reflect the current program to remain useful.

Explain why clear and consistent documentation is essential for PLC programs.

Think about how documentation helps when you are not the original programmer.

List the main sections you would include in a PLC program documentation file.

Consider what information someone new to the program would need.

Practice

1. Why is it important to include documentation in a PLC program?

easy

A. It automatically fixes errors in the program.

B. It makes the program run faster.

C. It reduces the size of the program file.

D. It helps others understand and maintain the program easily.

Solution

1. Step 1: Understand the purpose of documentation

   Documentation explains the program's purpose and logic to others.

2. Step 2: Identify benefits of documentation

   It helps maintain and update the program without confusion.

3. Final Answer:

   It helps others understand and maintain the program easily. -> Option D

4. Quick Check:

   Documentation improves understanding = A [OK]

Hint: Documentation = easier understanding and maintenance [OK]

Common Mistakes:

• Thinking documentation speeds up program execution
• Assuming documentation reduces program size
• Believing documentation fixes errors automatically

2. Which of the following is the correct way to add a comment in a PLC program?

easy

A. (* This is a comment *)

B. # This is a comment

C. // This is a comment

D.

Solution

1. Step 1: Identify comment syntax in PLC programming

   Many PLC languages use (* ... *) for comments.

2. Step 2: Compare options

   // is for C-like languages, # for scripting, for HTML, so only (* ... *) fits PLC.

3. Final Answer:

   (* This is a comment *) -> Option A

4. Quick Check:

   PLC comments use (* ... *) = C [OK]

Hint: PLC comments use (* and *) symbols [OK]

Common Mistakes:

• Using // or # which are not standard in PLC
• Confusing HTML comments with PLC comments
• Leaving out comment delimiters

3. Given this comment in a PLC program: (* Input: Start button, Output: Motor *), what is the main purpose of this comment?

medium

A. To optimize the motor control logic.

B. To execute the motor when the start button is pressed.

C. To describe the program's inputs and outputs clearly.

D. To declare variables for the start button and motor.

Solution

1. Step 1: Read the comment content

   The comment states inputs and outputs: Start button and Motor.

2. Step 2: Understand comment purpose

   Comments explain code parts, not execute or declare variables.

3. Final Answer:

   To describe the program's inputs and outputs clearly. -> Option C

4. Quick Check:

   Comments explain inputs/outputs = D [OK]

Hint: Comments explain, not execute or declare [OK]

Common Mistakes:

• Thinking comments run code
• Confusing comments with variable declarations
• Assuming comments optimize logic

4. A PLC program has this comment: (* Author: John Doe Purpose: Control conveyor speed *) but it is missing input and output details. What is the best fix?

medium

A. Remove the author name to save space.

B. Add comments describing inputs and outputs clearly.

C. Delete the comment because it is incomplete.

D. Add code to automatically generate comments.

Solution

1. Step 1: Identify missing documentation parts

   The comment lacks input and output descriptions which are important.

2. Step 2: Choose the best way to improve documentation

   Adding clear input/output comments improves understanding and maintenance.

3. Final Answer:

   Add comments describing inputs and outputs clearly. -> Option B

4. Quick Check:

   Complete comments include inputs/outputs = B [OK]

Hint: Complete comments include inputs and outputs [OK]

Common Mistakes:

• Removing author info unnecessarily
• Deleting useful comments
• Expecting code to auto-generate comments

5. You need to document a complex PLC program controlling multiple machines. Which approach best follows PLC program documentation standards?

hard

A. Write clear comments for each machine's inputs, outputs, logic, and author info.

B. Write one long comment at the start describing the whole program.

C. Skip comments to avoid clutter and rely on variable names only.

D. Use technical jargon to impress other engineers.

Solution

1. Step 1: Understand documentation needs for complex programs

   Complex programs need clear, organized comments for each part.

2. Step 2: Evaluate options for clarity and standards

   Clear comments per machine with inputs, outputs, logic, and author info follow best practices.

3. Final Answer:

   Write clear comments for each machine's inputs, outputs, logic, and author info. -> Option A

4. Quick Check:

   Clear, organized comments = A [OK]

Hint: Document each part clearly with inputs, outputs, logic [OK]

Common Mistakes:

• Writing only one big comment
• Skipping comments entirely
• Using confusing technical jargon