A Quick Guide to PLC Programming Algorithms in 1 Minute

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Learn the fundamentals of PLC programming algorithms, including switch, analog, and pulse signal processing, in this comprehensive guide designed for industrial automation professionals.

In the world of PLC programming, mastering the three core signal types—switch signals, analog signals, and pulse signals—is crucial. By understanding the relationships between these signals, you can unlock the full potential of PLC systems for industrial automation.

1. Understanding the Basics

Switch Signals: The Foundation of PLC Control

Also known as logic signals, switch signals represent binary states: 0 or 1, ON or OFF. This type of control is the most fundamental and widely used in PLC systems.

  • Objective: The goal of switch signal control is to produce corresponding outputs based on the combination of current inputs and their historical sequence. This enables the system to operate in a specific order, a principle often referred to as sequential control.
  • Types: Sequential control can be divided into manual, semi-automatic, and automatic operations, with control principles ranging from distributed to centralized and hybrid systems.

Analog Signals: Managing Continuous Data

Analog signals represent continuously changing physical quantities, such as voltage, current, pressure, speed, and flow.

  • Conversion: Analog signals are converted into digital signals using sensors and transducers. For example, a temperature range of 0–100°C can be converted into a digital value ranging from 0 to 32767 in a PLC with 1/32767 resolution.
  • Standardized Signals: Signals such as 4–20mA, 1–5V, and 0–10V are commonly used. Analog input/output modules (A/D and D/A) handle the conversion between these signals and digital values.
  • Control Types: Analog signal control, also known as process control, includes feedback control, feedforward control, proportional control, and fuzzy control.

Pulse Signals: The Driving Force for Precision Control

Pulse signals alternate between 0 (low) and 1 (high) at specific frequencies, making them ideal for position, motion, and trajectory control.

  • Application: For example, controlling the rotation of a stepper motor involves calculating the required number of pulses. If the motor requires 10,000 pulses per revolution and must rotate 90 degrees, the formula is:
    Pulse Count = Total Pulses per Revolution × (Desired Angle ÷ 360°).
    In this case, it would be 2500 pulses.

2. Analog Signal Calculation

Understanding signal resolution and data conversion is essential for precise analog signal processing.

Common Analog Signal Ranges and Resolutions:

  • -10 to 10V: At 6000 resolution, the signal is converted to -3000 to 3000 (Hex: F448 to 0BB8).
  • 0 to 10V: At 12000 resolution, the signal is converted to 0 to 12000 (Hex: 0 to 2EE0).
  • 4 to 20mA: Similarly, at 12000 resolution, the range is 0 to 12000.

Practical Wiring Tips for Analog Inputs:

  1. Use shielded twisted-pair cables, but avoid connecting the shield.
  2. Short-circuit unused inputs between the VIN and COM terminals.
  3. Isolate analog signal lines from power lines to reduce interference.
  4. Use filters when power lines are noisy.
  5. Always power the CPU unit before the load, and reverse the sequence when shutting down.

3. Pulse Signal Calculation

Pulse signals are essential for controlling stepper motors, servo motors, and other precision devices. Below are common control methods:

Angle Control for Stepper Motors:

  1. Determine the total number of pulses required per revolution.
  2. Calculate the angle percentage using the formula:
    Pulse Count = Total Pulses per Revolution × (Set Angle ÷ 360°).

Distance Control for Stepper Motors:

  1. Calculate the circumference of the roller using its diameter: Circumference = Diameter × π.
  2. Determine the pulse count required for the set distance:
    Pulse Count = Set Distance ÷ (Circumference ÷ Pulses per Revolution).

Position Control:

This combines angle and distance control for precise motion execution.

Servo Motor Considerations:

Servo motors require additional calculations for electronic gear ratios and reduction ratios to account for internal configurations.

4. Advanced Techniques for PLC Programming

Tips for Control Expert Configuration:

  • Set Redundant Modes: Enable “Hot Standby” for critical systems.
  • Synchronize Data: Define critical data for efficient synchronization to reduce network load.
  • Test Switch-Over Times: Use simulation tools to test response times and optimize performance.
Wiring PLC Control panel with wires industrial factory

Why PLC Programming Algorithms Matter

Understanding these fundamental algorithms allows engineers to unlock the full capabilities of PLC systems, improving efficiency, accuracy, and reliability in industrial automation. From managing complex analog signals to executing precise pulse controls, mastering these techniques ensures seamless operations across diverse applications.