Programming and PLCs

Programmable Logic Controllers (PLCs) are essential in industrial automation for controlling machinery and processes. Understanding the programming formulas and techniques used in PLC programming is crucial for optimizing and troubleshooting automation systems.

Binary Arithmetic in PLCs

Binary arithmetic is fundamental in PLC programming, as PLCs operate using binary logic. Here are some common binary arithmetic operations:

1. Binary Addition

Binary addition is similar to decimal addition but follows binary rules. The possible outcomes are:

• 0 + 0 = 0
• 0 + 1 = 1
• 1 + 0 = 1
• 1 + 1 = 10 (which is 0 with a carry of 1)

Example Calculation: Add binary numbers 1011 and 1101.

Solution:

• 1011
• +1101
• ------
• 11000

2. Binary Subtraction

Binary subtraction follows similar rules to binary addition, with borrowing as needed. The possible outcomes are:

• 0 - 0 = 0
• 1 - 0 = 1
• 1 - 1 = 0
• 0 - 1 = 1 (with a borrow from the next higher bit)

Example Calculation: Subtract binary number 1101 from 10101.

Solution:

• 10101
• - 1101
• -------
• 10000

Ladder Logic Programming

Ladder logic is a graphical programming language used to develop software for PLCs. It uses symbols that mimic the layout of relay logic diagrams. Here are some basic elements of ladder logic:

1. Contacts

Contacts represent input conditions. There are two types:

• Normally Open (NO): Passes power when the input is true.
• Normally Closed (NC): Passes power when the input is false.

2. Coils

Coils represent outputs. When powered, they activate the output device.

3. Timers

Timers delay actions for a specified period. Types of timers include:

• On-Delay Timer (TON): Delays turning on the output.
• Off-Delay Timer (TOF): Delays turning off the output.

4. Counters

Counters count events. Types of counters include:

• Up Counter (CTU): Increments the count.
• Down Counter (CTD): Decrements the count.

Mathematical Operations in PLCs

PLCs can perform various mathematical operations, including addition, subtraction, multiplication, and division.

1. Addition

Adds two numbers together.

Formula: Result = A + B

2. Subtraction

Subtracts one number from another.

Formula: Result = A - B

3. Multiplication

Multiplies two numbers together.

Formula: Result = A × B

4. Division

Divides one number by another.

Formula: Result = A / B

Example PLC Program

Here is an example of a simple PLC program using ladder logic to control a motor:

    +------------------+
    | Start | Stop     |
    |  --[ ]--|--[ ]-- |
    |         |        |
    |         |        |
    |         +-[ ]----+
    |         | Motor  |
    |         +-[M]----+
    +------------------+
  

Explanation:

• Start: Normally open contact for the start button.
• Stop: Normally closed contact for the stop button.
• Motor: Output coil for the motor.