IEC 61131-3 Programmable Logic Controllers (PLC)
Last Updated: January 16, 2025 Reviewed by: Mohsen Mostafaei, consulting engineer
Description
IEC 61131-3 is the third part of the IEC 61131 standard that establishes a standardized programming interface for Programmable Logic Controllers. It defines five programming languages: Ladder Diagram (LD), Function Block Diagram (FBD), Structured Text (ST), Instruction List (IL), and Sequential Function Chart (SFC). This standard provides a unified framework for PLC programming, ensuring consistency across different manufacturers and platforms while maintaining a structured approach to industrial automation programming.
Working Principle
The standard operates by providing a common architectural model that defines program organization units, including functions, function blocks, and programs. These elements can be written in any of the five programming languages and are organized within a hierarchical structure. The execution model follows a cyclic scan pattern where inputs are read, the program is executed, and outputs are updated. Variables are strictly typed and can be declared as local, global, or directly represented I/O, enabling structured data handling and program flow control. The standard implements both graphical and textual programming methods, allowing programmers to choose the most suitable approach for their specific requirements.
Applications
IEC 61131-3 is extensively used in automotive manufacturing lines for coordinating robotic assembly operations and managing paint booth sequences. In pharmaceutical manufacturing, it controls batch processes, maintaining precise temperature and pressure parameters during drug production. Water treatment facilities utilize it for managing multiple pumping stations, chemical dosing systems, and filtration processes. The standard is also implemented in food and beverage production lines, controlling pasteurization temperatures, filling operations, and packaging systems. In steel mills, it manages complex rolling mill operations, temperature control systems, and material handling sequences.
Advantages over other Programmable Logic Controllers (PLC)
IEC 61131-3 compliant systems offer superior interoperability, allowing programs to be transferred between different manufacturers' hardware with minimal modification. The structured programming approach reduces debugging time by approximately 30% compared to non-standardized systems. The ability to mix programming languages within a single project enables optimized solutions - for example, using Sequential Function Charts for process sequences while implementing complex calculations in Structured Text. The standard's strict variable declaration requirements reduce memory allocation errors by approximately 40% compared to proprietary systems.
Limitations
The standard does not address real-time performance specifications, leaving timing-critical applications subject to hardware-specific implementations. Complex motion control applications often require manufacturer-specific extensions beyond the standard's scope. The learning curve for utilizing all five programming languages effectively is steep, typically requiring 6-12 months of dedicated training. Implementation variations between different manufacturers can still cause compatibility issues, particularly with advanced features and specialized function blocks.
Considerations
Initial implementation costs typically range from $5,000 to $50,000, depending on system size and complexity. Training costs average $2,000-$5,000 per programmer. Annual maintenance costs generally run 10-15% of the initial investment, including software updates and technical support. Hardware durability is typically 10-15 years in normal industrial environments, though software updates may be required every 3-5 years to maintain compatibility with newer systems. Programming tools require annual licensing fees ranging from $500 to $3,000 per development seat. System migration costs between different manufacturers can range from 20-40% of the initial implementation cost, even with standard compliance.
from Sichuan Odot Automation System Co., Ltd.
The C4374 follows the IEC61131-3 international standard programmable logic controller, supports ladder diagram (LD), instruction list (IL), structured text (ST), function block diagram (CFC/FBD), sequential function chart (SFC) five programming languages, user program storage supports 4 Mbytes, data... [See More]
- Program Languages: IEC61131-3; IEC61131-3(LD、IL、ST、CFC/FBD、SFC)
- Baud Rate: 115200
- Computer Interface Options: Single Serial Interface; 3*RJ45，1*RS485，1*CAN
- Network Options: CANbus
from Sichuan Odot Automation System Co., Ltd.
The B2341 programming environment is Codesys, a programmable controller that. follows the IEC61131-3 international standard, and supports five programming. languages: ladder diagram (LD), instruction list (IL), structured text (ST), function. block diagram (CFC), and sequential function diagram... [See More]
- Program Languages: IEC61131-3; IEC61131-3(LD, IL, ST, CFC, SFC)
- Operating Temperature: -4 to 122
- Computer Interface Options: 2*RJ45
from Sichuan Odot Automation System Co., Ltd.
#183; Supports optional Profinet and EtherCAT masters, with future support for IO-Link, EtherNet/P, and more. · The world's first commercially available IEC61499+Profinet solution utilizes IEC61499 standards, including distributed, hardware-software decoupling, and object-oriented design. [See More]
- Program Languages: IEC61131-3; IEC61499
- Mounting Options: DIN Rail
- Network Options: Ethernet
- Operating Temperature: -4 to 140
from Delta Electronics (Americas)
Highly integrated software ISPSoft: Graphical Interface with 5 programming languages. Enhanced flexibility: Max. 100m between 2 local extension racks. Improved maintainability: Hot-swapping function keeps the system running [See More]
- Program Languages: IEC61131-3; Sequential Function Chart; Function Block Diagram; Ladder Diagram; Structured Text; Instruction List
- Inputs: 0
- Total Points: 4352
- Outputs: 0
from STW Technic
Designed for harsh environments, freely programmable [See More]
- Program Languages: IEC61131-3; Sequential Function Chart; Function Block Diagram; Ladder Diagram; Structured Text; Instruction List; Relay Ladder Logic; Flow Chart; C Programming Language
- Inputs: 24
- Total Points: 36
- Outputs: 12
from OMEGA Engineering, Inc.
The ADAM-5510KW series is designed to monitor and control processes through multi-channel I/O modules. Each system is capable of handling up to 4 or 8 I/O modules for channel capacities up to 128 I/O points. Depending on the type and number of I/O points a system can be configured to meet your... [See More]
- Program Languages: IEC61131-3; Sequential Function Chart; Function Block Diagram; Ladder Diagram; Structured Text; Instruction List
- Input: DC Input (optional feature); AC Input (optional feature); Thermocouple Input (optional feature); RTD Input (optional feature); Frequency or Pulse (optional feature)
- Total Points: 128
- Output: DC Output (optional feature); Relay Output (optional feature); Analog Output (optional feature)
from Delta Electronics (Americas)
The Delta Compact Modular Mid-range PLC AS Series is a high performance multi-purpose controller designed for all kinds of automated equipment. It features Delta's self-developed 32-bit SoC CPUs for enhanced execution speed (40 k steps/ms) and supports up to 32 extension modules or up to 1,024... [See More]
- Program Languages: IEC61131-3; Sequential Function Chart; Ladder Diagram; Structured Text; CFC
- Inputs: 16
- Total Points: 32
- Outputs: 16
from Delta Electronics (Americas)
Delta's DVP series programmable logic controllers offer high-speed, stable and highly reliable applications in all kinds of industrial automation machines. In addition to fast logic operation, bountiful instructions and multiple function cards, the cost-effective DVP-PLC also supports various... [See More]
- Program Languages: IEC61131-3; Sequential Function Chart; Ladder Diagram; Instruction List
- Inputs: 36
- Total Points: 60
- Outputs: 24