Best Practices for PLC Tag and Address Naming Conventions

• PLC (Programmable Logic Controller) tag naming conventions refer to the systematic way in which tags, or variables, within a PLC program are named. 
• These conventions are established to ensure clarity, consistency, and ease of understanding when working with the PLC program, particularly in larger projects where multiple engineers might collaborate or where maintenance and troubleshooting are required over time.
• The core of industrial automation is made up of programmable logic controllers, or PLCs, which coordinate complex operations in a variety of industries, from manufacturing to energy management. 
• The labeling of tags, which function as variables and represent inputs, outputs, memory locations, timers, and control signals inside the system, is essential to PLC programming. 
• To ensure PLC programming is clear, consistent, and easy to comprehend, effective tag labeling is crucial. 
• This helps to make development, troubleshooting, and maintenance procedures run more smoothly. In this comprehensive guide, we explore the significance of PLC tag and address naming conventions and provide insights into crafting efficient and standardized labels.

Importance of PLC Tag and Address Naming Conventions

Clarity and Understanding

• Well-structured tag and address labels facilitate comprehension of PLC programs by programmers, maintenance personnel, and stakeholders involved in automation processes. 
• Uncertainty and the chance of mistakes during programming and maintenance tasks are reduced when clear labels are used to communicate the purpose, placement, and importance of each tag.

Consistency and Standardization

• Standardized naming conventions ensure consistency across PLC programs, enabling seamless collaboration among multiple engineers and facilitating the integration of new components or modifications into existing systems. 
• Consistent tag and address labeling enhance readability, streamline troubleshooting processes, and promote efficient system management.

Efficient Troubleshooting

• Simple tag and address labels make debugging tasks faster by allowing engineers to locate important PLC program components with easily.
• When combined with logical organization and methodical naming practices, descriptive names enable maintenance staff to identify problems, diagnose errors, and take immediate corrective action, reducing downtime and maximizing system reliability.

Scalability and Maintainability

• PLC systems are more scalable and maintainable when robust tag and address labeling procedures are followed, especially in large-scale industrial settings with intricate automation procedures. 
• Clear labels make it easier to upgrade systems, allow for future expansions, and ensure that PLC programs are understandable and controlled during their entire lifecycle.

Components of PLC Tag and Address Naming Conventions

In PLC programming, the naming conventions for tags and addresses are critical for ensuring clarity, consistency, and efficiency in system design, development, and maintenance. 

Let’s explore the key components in detail:

Prefixes or Identifiers

• Prefixes categorize tags based on their type or function within the PLC system, providing a clear indication of their purpose. 
• Common prefixes include:

I_: Input tags representing signals from external sensors or devices.

O_: Output tags controlling actuators or devices.

M_: Memory tags for internal storage, such as counters and timers.

T_: Timer tags used for time-based operations.

C_: Control tags for system control signals.

• Prefixes help organize and differentiate between different types of tags, making it easier for programmers and maintenance personnel to understand and work with them.

Descriptive Names

• Within the PLC system, descriptive names provide a brief description of the purpose, location, or importance of each tag. 
• Programming, maintenance, and troubleshooting procedures become more effective when meaningful labels are used to improve readability and comprehension. 

For example:

I_Temperature_Tank1: Input tag for temperature measurement in Tank 1.

O_Valve_Main: Output tag controlling the main valve.

M_Count_Product_A: Memory tag counting products on line A.

Descriptive names provide valuable context and information about the purpose of each tag, making it easier to understand and manage the PLC program.

Sub-tags

By adding more information and depth to the primary tag, sub-tags further classify or define its elements. Adding sub-tags improves the readability and precision of tag labels, making it easier to precisely identify and use them in the PLC program.

Examples include

I_Temperature_Tank1_Setpoint: Input tag for the setpoint temperature of Tank 1.

O_Valve_Main_Position: Output tag indicating the position of the main valve.

Sub-tags help organize related information within the tag name, making it easier to navigate and understand complex PLC programs.

Numeric Suffixes

• Numeric suffixes differentiate between multiple instances of similar tags, allowing for scalability and organization within the PLC program. Sequential numbering or specific identifiers denote distinct components or instances of a particular tag type, facilitating systematic arrangement and easy reference. 

For instance:

I_Temperature_Tank2

O_Valve_Secondary

• Numeric suffixes help avoid naming conflicts and provide a structured way to manage and reference multiple instances of the same type of tag.

Use of Underscores or CamelCase

• Utilizing underscores (_) or CamelCase (no spaces, with each word capitalized except the first) enhances the readability of tag labels, ensuring clarity and consistency in PLC programming. 
• Clear formatting conventions mitigate confusion and streamline communication among engineers and stakeholders involved in the automation process.

Let’s illustrate the use of underscores (_) and CamelCase with an example of a PLC tag for a temperature sensor:

Underscores (_)

Tag Name: temperature_sensor

• In this format, each word is separated by an underscore. 
• This tag name clearly indicates that it pertains to a temperature sensor. It is concise and easy to read, making it suitable for situations where clarity and brevity are important.

CamelCase

Tag Name: temperatureSensor

• In CamelCase format, each word is concatenated without spaces, and each subsequent word starts with a capital letter except the first. 
• This tag name also indicates that it refers to a temperature sensor. The lack of spaces and consistent capitalization make it easy to read and distinguish from other tag names.

Abbreviations

Abbreviations may be employed to condense lengthy terms or commonly used phrases, provided that they are standardized and easily comprehensible to all users. Careful consideration of abbreviations ensures that tag labels remain concise without sacrificing clarity or precision.
Abbreviations help reduce the length of tag names while preserving their meaning and readability, making the PLC program more concise and manageable.

Let’s consider an example where abbreviations are used to condense lengthy terms in a PLC tag:

Original Tag Name: temperature_sensor_room1

Abbreviated Tag Name: temp_sensor_rm1

In this example, the original tag name temperature_sensor_room1 is quite lengthy. To make it more concise while preserving its meaning, abbreviations are used.

• temp is an abbreviation for “temperature.”
• sensor remains unchanged as it is a commonly used term in PLC programming.
• rm1 is an abbreviation for “room1.”

By employing these abbreviations, the tag name temp_sensor_rm1 achieves the goal of reducing the length of the original tag while still conveying the same information about the type of sensor (temperature sensor) and its location (room1)..

Tag Naming Styles According to IEC Standards

PLC tag names can adhere to various naming styles outlined in IEC standards:

Camel Style

Each word in the tag name starts with a capital letter, and there are no underscores between words. For example, m101CompressorRunCommand.

Pascal Style

Similar to Camel Style, but the first letter is always capitalized. For instance, M101CompressorRunCommand.

Snake Style

Words in the tag name are separated by underscores. For example, M101_Compressor_Run_Command.

Address-Based PLC Tags

• Years ago, it was common practice for PLC tags to represent memory addresses within the PLC’s memory. 
• Tags such as N7:2.3 or B3:1.2 were standard for Allen-Bradley controllers like the SLC 500 or MicroLogix series. 
• These tags directly mapped to specific memory locations but lacked human-readable context.

Example:

N7:2.3 – Represents a memory location in the N7 data table, with an offset of 2 and bit 3.

B3:1.2 – Represents a memory location in the B3 data table, with an offset of 1 and bit 2.

Name-Based PLC Tags

• Modern PLC controllers allow for the use of human-readable tag names that represent functions or elements within the system. 
• Tags like “Motor_Run_Command” or “Valve_Open” provide clear context and are easier to understand compared to raw memory addresses.

Example:

Motor_Run_Command – Represents the command to run a motor.

Valve_Open – Represents the status of an open valve.

In contrast to name-based PLC tags, which provide clear context and are easier to understand, address-based tags were primarily used due to historical reasons and limitations in older PLC systems. However, with advancements in PLC technology and software, name-based tags have become more prevalent, offering improved clarity, maintainability, and ease of use in modern industrial automation systems.

Hierarchy and Organization

In larger PLC programs, organizing tags hierarchically plays a crucial role in maintaining clarity and ease of navigation. By structuring tags in a hierarchical manner, programmers can reflect the physical or logical layout of the system, making it easier to understand and manage. 

Here are some strategies for organizing PLC tags hierarchically:

By Equipment or Device

• Grouping tags based on the equipment or devices they represent is a common approach. 
• For example, in a manufacturing plant, tags related to motors, pumps, valves, and sensors can be grouped under their respective equipment categories. This structure might look like:

Motors

└── Motor1

    ├── Motor1_Run_Command

    ├── Motor1_Speed_Setpoint

    └── …

Pumps

└── Pump_A

    ├── Pump_A_Run_Command

    ├── Pump_A_Flow_Rate

    └── …

By Process Stage or Area

• If the system consists of multiple process stages or areas, organizing tags based on these divisions can be beneficial. 
• For instance, in a water treatment facility, tags can be grouped according to stages such as filtration, disinfection, and distribution:

Filtration

├── Filtration_Pump

├── Filtration_Valve

└── …

Disinfection

├── Chlorine_Monitor

├── UV_Sterilizer

└── …

By Functional Area or Subsystem

• Tags can also be organized by functional areas or subsystems within the overall system. 
• For example, in a packaging line, tags might be grouped by subsystems such as conveyor systems, labeling machines, and sorting mechanisms:

Conveyor_System

├── Conveyor_Motor

├── Conveyor_Speed_Sensor

└── …

Labeling_Machine

├── Labeling_Motor

├── Labeling_Position_Sensor

└── …

Mixed Hierarchy

• In practice, a combination of these approaches is often used to achieve the most logical and intuitive organization. 
• For instance, a PLC program for a manufacturing plant might incorporate hierarchical structures based on equipment, process stages, and functional areas to ensure comprehensive organization and clarity.

By adopting a hierarchical organization for PLC tags, programmers can enhance readability, facilitate troubleshooting, and streamline maintenance procedures, ultimately contributing to the overall efficiency and reliability of the industrial automation system.

Guidelines for Establishing PLC Tag and Address Naming Conventions

When establishing PLC tag and address naming conventions:

• Clarity:  To minimize misunderstandings during programming and maintenance, make sure tag names express their function and location inside the system.
• Consistency: Adopt uniform naming conventions for all PLC programs to promote consistency and make system integration and engineer collaboration easier.
• Descriptive: Give each tag a name that is helpful in explaining its purpose and improving readability and comprehension for all parties involved.
• Logical Organization: To make navigation easier, tag information should be arranged hierarchically according to equipment, process steps, or functional regions. This should reflect the system’s physical or logical layout.
• Avoid  Confusion: To avoid mistakes and misunderstandings, make sure every tag name in the PLC program is distinct and clear.
• Scalability:Create naming guidelines that support future system additions or upgrades as well as the methodical insertion of new tags.
• Human-Readable: Prioritize tag names that are easy to understand and interpret by personnel involved in PLC programming, maintenance, and troubleshooting.
• Documentation and Training: Document the chosen naming conventions and provide training to ensure all team members understand and adhere to them consistently.
• Standards Compatibility: Align naming conventions with relevant industry standards or guidelines to promote interoperability and compatibility with other systems.
• Feedback and Iteration: Seek feedback from stakeholders and regularly review naming conventions to identify areas for improvement and ensure ongoing effectiveness. Iterative refinement can lead to more optimized PLC programming practices over time.

Five Essential Tips for PLC Tag and Address Naming Conventions

To ensure efficiency, consistency, and clarity while creating naming conventions for PLC tags and addresses, it’s important to take into account a number of aspects. 

Here are five crucial pointers to help you with your approach:

Descriptive Naming

• Make that tag names accurately convey how they work within the system, including technician-friendly standard terminology and abbreviations to facilitate speedier troubleshooting. 
• When needed, include descriptions to give more background information.

Organizational Prefixes

• To help programmers and technicians locate tags more easily and to help with alphabetical or numerical categorization, start tags with a consistent letter or number to indicate the purpose or area.

Formatting for Readability

• Use capitalization or underscores (_) to improve tag readability. 
• This will increase comprehension and lower the chance of errors during programming and maintenance tasks.

Pre-Assignment of Local Tags

• Assigning all tags for a particular assembly or program before duplication, if applicable, can save time and guarantee consistency between duplicate programs by eliminating the need for manual tag assignment.

Use of Spreadsheets for Tag Creation

• Instead of manually entering tags into databases, use spreadsheets to create tags. 
• This will make it easier to increment tags, avoid duplication, and ensure consistency across design and programming stages. 
• The process of creating tags is streamlined by using spreadsheet capabilities to facilitate simpler export/import of tags into PLC platforms.

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