PLC Industry Standards and Guidelines

Programmable Logic Controllers (PLCs) are widely used in industrial automation to control machinery, production lines, and critical processes. To ensure safety, reliability, compatibility, and efficiency, global industry standards and guidelines govern how PLC systems are designed, programmed, and maintained.
Adhering to these standards not only improves technical performance but also ensures legal compliance in regulated sectors such as pharmaceuticals, energy, and food manufacturing. In modern automation, where PLCs often interact with IoT devices, AI-based monitoring tools, and cloud systems, understanding these guidelines is critical for long-term scalability and interoperability.

These standards help manufacturers, engineers, and industries establish best practices for PLC programming, hardware selection, network integration, safety, cybersecurity, and interoperability. Understanding these industry standards is crucial for ensuring compliance with regulatory requirements and best practices in automation.
Following recognized standards also allows teams from different countries or vendors to collaborate more easily, since the terminology, programming methods, and safety protocols remain consistent across projects.

1. IEC 61131: PLC Programming Language Standard

The International Electrotechnical Commission (IEC) 61131 standard defines the official programming languages for PLCs. It ensures that PLC programs are structured, efficient, and maintainable, improving interoperability across different brands and models.
This reduces the learning curve for engineers moving between brands like Siemens, Allen-Bradley, Mitsubishi, and Omron, making workforce training more efficient and cost-effective.

Programming Languages Under IEC 61131

• Ladder Diagram (LD): Graphical representation based on relay logic, commonly used for machine control.
• Function Block Diagram (FBD): Uses predefined functional blocks. Ideal for process automation.
• Structured Text (ST): High-level, text-based language similar to Pascal or C for complex logic.
• Instruction List (IL): Low-level language resembling assembly code. Found in legacy systems.
• Sequential Function Chart (SFC): Graphical language for modeling sequential operations.

Why is IEC 61131 Important?

• Ensures consistency across different PLC brands
• Promotes standardized programming practices
• Helps engineers write maintainable, reusable code

More Info: Available on the IEC official website.

2. ISA-88: Batch Process Control Standard

The ISA-88 standard (also known as S88) is a framework for batch process control in industries such as pharmaceuticals, food and beverage, and chemical processing.
It is especially valuable where multiple products are made using shared equipment, as it separates recipe data from control logic, allowing faster product changeovers without modifying the main PLC program.

Key Concepts of ISA-88

• Process Model: Defines units, equipment modules, and phases for batch automation.
• Procedural Model: Specifies how batch sequences are executed.
• Equipment and Recipe Management: Ensures consistent production across batches.

Why is ISA-88 Important?

• Improves consistency and repeatability
• Simplifies batch automation and scalability
• Reduces engineering time and effort

More Info: Available on the ISA website.

3. ISA-95: Enterprise-Control System Integration

The ISA-95 standard (also known as IEC 62264) defines how automation systems integrate with enterprise-level business systems.
It bridges the gap between shop floor automation and corporate decision-making systems, enabling seamless communication between MES, ERP, SCADA, and PLC layers. This helps companies optimize production schedules, manage inventory in real-time, and align manufacturing output with customer demand.

Key Features of ISA-95

• Defines control system hierarchy:
  • Level 4: Enterprise Resource Planning (ERP)
  • Level 3: Manufacturing Execution Systems (MES)
  • Level 2: SCADA, HMIs, control systems
  • Level 1: Sensors, actuators, PLCs
• Standardizes data exchange between business and automation layers

Why is ISA-95 Important?

• Enables real-time decision-making and analytics
• Integrates IT and OT systems
• Optimizes production performance

More Info: Visit ISA’s official website.

4. NFPA 70E: Electrical Safety in Industrial Automation

The NFPA 70E standard focuses on electrical safety in workplaces, especially when dealing with high-voltage PLC cabinets and control systems.
Regular training on NFPA 70E protocols ensures that engineers and technicians can work safely on energized equipment, reducing the risk of accidents and avoiding costly downtime.

Key Safety Guidelines

• Arc Flash Risk Assessment: Identifies potential arc flash hazards.
• Lockout/Tagout (LOTO): Ensures equipment is de-energized before servicing.
• Personal Protective Equipment (PPE): Specifies safety gear for working on PLCs.

Why is NFPA 70E Important?

• Reduces risk of injury and accidents
• Ensures OSHA compliance
• Minimizes downtime from electrical incidents

More Info: Visit NFPA.org.

5. ANSI/ISA-99 (IEC 62443): Cybersecurity for Industrial Automation

With increasing cyber threats, the ANSI/ISA-99 standard (also known as IEC 62443) provides a framework for securing industrial control systems like PLCs and SCADA.
In today’s connected plants, PLCs often communicate over Ethernet and wireless networks, making them potential entry points for hackers. This standard helps organizations implement layered defenses, incident response plans, and ongoing vulnerability assessments.

Key Cybersecurity Measures

• Secure Network Segmentation: Isolates PLCs from corporate networks
• Access Control: Uses multi-factor authentication (MFA)
• Data Encryption: Protects PLC communication
• Security Audits: Routine risk assessments and testing

Why is ANSI/ISA-99 Important?

• Prevents cyberattacks on industrial systems
• Enables secure remote access to PLCs
• Protects critical infrastructure sectors

More Info: Available on ISA’s cybersecurity portal.

6. ISO 9001: Quality Management in Automation

ISO 9001 is a global standard for quality management that applies to PLCs, industrial processes, and automation systems.
When applied to automation projects, ISO 9001 ensures that documentation, testing, and commissioning follow a repeatable and auditable process, which is essential for long-term maintenance and customer satisfaction.

Key Principles

• Process Optimization: Encourages continual improvement
• Customer Satisfaction: Focus on meeting performance expectations
• Risk-Based Thinking: Helps identify and mitigate project risks

Why is ISO 9001 Important?

• Improves quality and consistency in PLC projects
• Demonstrates compliance with regulations
• Builds customer confidence in automation solutions

More Info: Available at ISO.org.

7. How to Stay Updated with PLC Standards

Industrial automation is a fast-evolving field, and PLC-related standards are regularly revised to address new technologies, safety requirements, and cybersecurity threats.
Engineers, technicians, and automation managers must actively keep their knowledge current to ensure their systems remain compliant and competitive.

Practical Ways to Stay Informed

• Professional Training & Certification: Enroll in accredited courses from organizations like ISA, IEC, or NFPA that offer official PLC certification and compliance training.
• Industry Conferences & Webinars: Participate in events focused on automation, Industry 4.0, and control system security.
• Membership in Standards Bodies: Join groups like ISA or IEEE to access draft standards, technical papers, and exclusive resources.
• Manufacturer Updates: Regularly review technical documentation and software release notes from PLC vendors such as Siemens, Allen-Bradley, and Omron.
• Online Communities: Engage in PLC-focused forums and LinkedIn groups where experts share updates, case studies, and troubleshooting tips.

By committing to continuous learning and staying up to date with PLC standards, professionals can ensure compliance, improve system efficiency, and reduce risks in their automation projects.

Industry standards and guidelines are essential for ensuring that PLC systems remain safe, reliable, and efficient. These frameworks help organizations:

• Ensure safety in PLC installations
• Improve reliability and performance
• Enhance cybersecurity protection
• Optimize integration between business and automation

Ultimately, understanding and applying these standards not only meets compliance requirements but also gives businesses a competitive advantage by enabling smoother integrations, reducing engineering costs, and improving system resilience.