Human-Machine Interface (HMI)

The Human-Machine Interface (HMI) plays a pivotal role in modern industrial automation, facilitating communication between operators and machines while providing easy access to process information. Over the years, HMI systems have evolved significantly - from simple control panels to sophisticated touchscreens featuring advanced graphics and integration with other systems. This guide delves into what HMI is, the components that enable its functionality, and the best practices for designing and programming such interfaces.

Definition and Importance of HMI

HMI (Human-Machine Interface) refers to systems designed to facilitate communication between humans and machines in industrial environments. These interfaces provide users with seamless access to process data and allow them to control various operations. Modern HMIs are employed in factories, power plants, HVAC systems, and many other industries, enabling operators to monitor process parameters, adjust settings, and respond to emergencies effectively.

HMI serves as a bridge between the human and machine worlds. Practically speaking, it grants access to the entire control system - from machine parameters to alarms, performance statistics, and much more. Operators gain full control over processes, enabling real-time decision-making and ensuring efficient operations.

What Does HMI Stand For?

HMI stands for Human Machine Interface. It is the screen, panel or software through which an operator monitors and controls a machine or process. A human machine interface shows process values, alarms and trends, and lets the operator start and stop equipment, change setpoints and acknowledge faults. In most installations the HMI does not control the process itself: the logic runs in programmable logic controllers (PLCs), and the HMI reads and writes PLC tags over an industrial network.

Where Is the HMI Located?

An HMI is usually located where the operator works: in the door of the control cabinet, on a pedestal next to the machine, or in a control room. On a single machine it is typically a 4-15 inch touch panel at machine level. In a large plant, PC-based HMI stations in the control room are combined with mobile HMI clients on tablets for maintenance staff.

Types of HMI

• Basic HMI - small panels with a few screens, buttons and alarms, used to control a single machine.
• Comfort or advanced HMI - larger touch panels with recipes, trends, user management, scripts and data logging.
• PC-based HMI - an industrial PC running HMI software, often used as a SCADA client.
• Web and mobile HMI - screens served by the PLC or HMI runtime and opened in a browser on a tablet or phone.

Evolution of HMI Systems

Initially, HMI systems were very basic - mainly consisting of panels with buttons, switches, and indicator lights. Operators used these panels to start and stop machines, while signal lights provided information about system status. As technology advanced, the first text displays emerged, enabling the presentation of basic process information.

Over time, graphical displays became the standard. Modern HMI systems now feature high-resolution, touch-sensitive, full-color screens capable of displaying complex graphics and charts. The next significant milestone in HMI evolution was their integration with SCADA and ERP systems, making process management and data access seamless across the entire organization.

Key Components of HMI Systems

An HMI system is composed of three essential elements: hardware, software, and communication protocols.

Hardware

The hardware forms the physical layer of the interface. This includes operator panels, industrial computers, or dedicated tablets designed to withstand harsh industrial conditions, such as vibrations, high humidity, or extreme temperatures. HMI hardware must ensure reliability and longevity to maintain seamless operations in challenging environments.

Software

Software is the soul of an HMI system. It defines how operators interact with machines. Various platforms are used to design interfaces that must be intuitive and user-friendly. Examples of such tools include Wonderware, Siemens WinCC, and Rockwell FactoryTalk.

FactoryTalk View Studio Machine Edition (ME)

FactoryTalk View Studio Machine Edition (ME) is one of the most versatile tools for creating HMI applications, offered by Rockwell Automation. Widely used in industrial environments, this platform enables the design of HMI screens tailored for integration with automation systems. ME supports features such as real-time process monitoring, alarm handling, and data visualization. It is particularly well-suited for developing solutions for PanelView Plus, one of the most popular devices used in industrial facilities.

FactoryTalk View Studio ME allows users to quickly design and deploy applications, significantly accelerating the implementation of new solutions in a factory setting. Its intuitive user interface and pre-configured components simplify development, even for less experienced users. Thanks to the HMI Tag Database feature, ME offers convenient management of all system variables, enhancing application clarity and facilitating future modifications.

Communication Protocols

Communication protocols are essential for exchanging information between the HMI and control systems, such as PLCs or sensors. Modern HMI systems support a wide range of protocols, including Modbus, Ethernet/IP, Profibus, Profinet, and OPC UA, ensuring versatility and seamless integration with various types of devices.

HMI vs SCADA: What Is the Difference?

SCADA stands for Supervisory Control and Data Acquisition. Both HMI and SCADA systems are used to monitor and control processes, so the terms are often mixed up. The difference is in scale and function:

Feature	HMI	SCADA
Scope	Single machine or line	Whole plant or many distributed sites
Main task	Operate and monitor a machine	Supervise, collect and archive data from many controllers
Hardware	Operator panel at machine level	Servers, client PCs, communication to many PLCs and RTUs
Data history	Limited, short-term trends	Long-term historian, reports, analytics
Typical software	WinCC Comfort, FactoryTalk View ME	WinCC Unified/Professional, Ignition, FactoryTalk View SE

In practice a SCADA system always includes HMI screens, but an HMI does not have to be part of a SCADA system. A packaging machine with one touch panel has an HMI; a water utility with 50 pump stations monitored from one control room uses SCADA.

Popular HMI Software

HMI software is used to create screens, link objects to PLC tags, configure alarms and download the project to the panel or runtime. The most common HMI solutions in industry include:

• Siemens WinCC in TIA Portal - WinCC Basic, Comfort, Advanced and Unified for SIMATIC HMI panels and PCs, fully integrated with S7-1200 and S7-1500 PLCs.
• Rockwell FactoryTalk View - Machine Edition for PanelView panels and Site Edition for SCADA applications.
• CODESYS Visualization - built into the CODESYS IDE, with TargetVisu and WebVisu options for PLCs from many vendors.
• Inductive Automation Ignition - a web-based HMI and SCADA platform.
• AVEVA (formerly Wonderware) InTouch - widely used HMI software for PC-based operator stations.

The choice usually depends on the PLC platform. With a Siemens PLC, WinCC in TIA Portal makes it easy to use the same tags in the PLC program and on the HMI screens, which eliminates the need to define the communication twice. If you work with CODESYS, see our guide to creating a CODESYS visualization.

The Process of Designing and Programming HMI

Creating an effective HMI system is a complex process that requires consideration of both technical and ergonomic aspects. This process can be divided into several key stages:

1. User Requirements Analysis

The first step in HMI design is understanding the needs of the operator and the requirements of the specific process. Engineers must analyze the application’s specifications, determine which information is critical for the operator, and identify the most frequently used functions.

2. User Interface Design

This stage focuses on designing the individual screens the operator will use. The interface must be clear, intuitive, and tailored to the specific application. Key information should be easily accessible, and alarm messages must be clear and understandable.

3. Implementation of Control Logic

Programming the HMI involves defining button actions, displaying process data, managing alarms, and ensuring communication with other devices. At this stage, designers outline the actions operators can take and the information they will have access to.

4. Testing and Validation

Every HMI system must undergo thorough testing before deployment. Testing involves verifying the correctness of all functions, assessing the system's response to errors, and simulating various scenarios that may arise in real-world conditions.

5. User Training

The final step is training the operators. Even the most well-designed system will be ineffective if users do not know how to operate it. Training should cover all aspects of system usage, including responding to alarms and troubleshooting potential issues.

Best Practices in HMI Design

To create an effective and secure HMI system, it is crucial to adhere to key design principles:

Simplicity and Clarity

One of the most important aspects of HMI design is simplicity. HMI screens should be clear, with information presented in an understandable manner. Avoid overcrowding a single screen with too much information, as this can confuse the operator and hinder decision-making.

Consistency

All screens should maintain consistency in terms of color scheme, layout, and the method of presenting information. Operators should be able to navigate seamlessly between different screens without encountering unexpected changes in operation or design. Consistency enhances usability and reduces the learning curve.

Responsiveness and Speed

The HMI system should respond instantly to operator actions. Any delay can lead to frustration and increase the risk of operational errors. Ensuring that all functions are quick and responsive is crucial for maintaining efficiency and usability.

Safety

Safety is a critical aspect of HMI design. The system should include robust access authorization mechanisms to ensure that only authorized personnel can modify critical process parameters. Additionally, alarm messages must be clear and easily understood, allowing operators to respond promptly and effectively to emergency situations.

Challenges in HMI Programming

Programming HMI systems can be challenging due to the complexity of the process and the diversity of environments in which they operate. Some of the key challenges include:

Integration with Diverse Systems

HMI systems must work seamlessly with a wide range of devices and control systems. Ensuring full compatibility with various communication protocols and enabling smooth integration with existing infrastructure is critical. This requires a deep understanding of both the hardware and software components involved.

Managing Large Amounts of Data

Industrial processes generate an enormous volume of data that must be efficiently processed and presented to operators. It is important to ensure the data is displayed in a clear and comprehensible manner, enabling operators to easily interpret the information and make informed decisions.

Adapting to User Needs

Operators have varying levels of experience and skill. It is crucial to design an interface that is intuitive and tailored to the needs of different user groups. Advanced features should be accessible for experienced operators, while the interface for beginners should remain simple and easy to navigate.

The Future of HMI Systems

The future of HMI systems is closely tied to the development of technologies such as the Internet of Things (IoT), Artificial Intelligence (AI), and Augmented Reality (AR). As these technologies become more widespread, HMI interfaces will be able to offer increasingly advanced features, including predictive analytics, intelligent recommendations, and interactive visualizations.

Integration with IoT will enable the collection of data from numerous sources and its centralized processing, facilitating even better process management. AI can assist in data analysis and decision-making, reducing operator workload and minimizing the risk of errors. Meanwhile, AR can provide more intuitive interactions with HMI systems, such as displaying critical information directly on an operator's visor for enhanced situational awareness.

The Impact of Artificial Intelligence on HMI

Artificial Intelligence (AI) brings a new level of capability to HMI systems, automating many tasks that previously required manual operator intervention. With AI, it is possible to predict machine failures, analyze usage patterns, and automatically fine-tune process parameters. For example, machine learning algorithms can analyze historical data to identify trends, enabling proactive maintenance and preventing potential breakdowns.

AI enhances the efficiency and reliability of industrial systems, making HMI a smarter and more adaptive tool in complex environments. By reducing operator workload and improving predictive capabilities, AI-driven HMI systems contribute to increased productivity and minimized downtime.

The Use of Augmented Reality in HMI

Augmented Reality (AR) opens up entirely new possibilities for HMI systems. Operators can use devices like AR glasses to receive real-time information about machine status without needing to look at traditional screens. This enhances mobility and enables better process monitoring in the field. For example, operators can view step-by-step repair instructions in real time, significantly reducing response times during equipment failures.

Cloud Integration with HMI

The integration of HMI systems with cloud computing is becoming increasingly important. Process data can be stored in the cloud, allowing for analysis from anywhere in the world. This provides operators and managers with real-time access to data, enabling better planning and quicker responses to changes. Additionally, the cloud simplifies the creation of backups, minimizing the risk of data loss due to local hardware failures.

Personalization of HMI Interfaces

Personalizing HMI interfaces is essential for improving operator efficiency. Each user has unique preferences and working styles, making the ability to customize screens to individual needs a growing standard. For example, operators can select which information is most critical to them and place it on the main screen. This approach enhances work comfort, reduces response times to events, and minimizes the likelihood of errors.

Application of Predictive Analytics

Predictive analytics is becoming increasingly common in HMI systems. Leveraging data collected from machines and AI algorithms, HMI systems can forecast when failures might occur or when maintenance is required. Operators are notified in advance about potential issues, allowing them to prevent downtime and reduce maintenance costs. These capabilities are especially critical in large production facilities, where every minute of downtime can result in significant losses.

Examples of HMI Applications in Industry

HMI systems are used across various industrial sectors. HMI systems play a crucial role in the food industry by enabling control over production processes, monitoring temperature and humidity, and managing packaging lines. Operators in the automotive industry use HMI to monitor robots, control assembly lines, and oversee quality assurance processes. In the energy sector, these systems help manage power grids, monitor turbine conditions, and control energy flows.

Ergonomics and HMI Interface Design

Ergonomics in HMI design is a critical factor influencing the efficiency and safety of operators. Designers must carefully arrange interface elements to ensure they are easily accessible and do not cause fatigue during extended use. Colors and fonts should be selected to minimize eye strain, and alarm messages must be distinctly differentiated from other information to ensure quick and accurate responses.

Application of Advanced Functions in HMI

Integration with SCADA and ERP

Modern HMI systems are increasingly integrated with SCADA (Supervisory Control and Data Acquisition) and ERP (Enterprise Resource Planning) systems. SCADA enables the collection, monitoring, and real-time analysis of process data, simplifying the management of multiple devices across various locations. Integration with ERP systems allows for synchronization of production data with managerial information, leading to efficient resource management and production optimization within the enterprise.

Monitoring the Technical Condition of Machines

HMI systems are also used for monitoring the technical condition of machines, which is essential for maintenance and preventing breakdowns. Through appropriate sensors, HMI can provide operators with data on component wear, oil levels, temperature, and other parameters that may impact the machine's condition. This enables operators to take timely maintenance actions, reducing the risk of costly downtime.

How to Program an HMI Step by Step

Regardless of the HMI software, a typical HMI programming workflow looks like this:

• Create the project and add devices - select the panel model and the PLC, and configure the network connection (for example PROFINET or EtherNet/IP).
• Define tags - link HMI tags to PLC variables. In integrated environments you can drag tags directly from the PLC program.
• Build the screens - an overview screen, detail screens for each part of the machine, an alarm screen and a settings screen.
• Configure alarms - discrete alarms from PLC bits and analog alarms with limits, with clear texts that tell the operator what to do.
• Add user management - operator, maintenance and engineer levels with different permissions.
• Simulate and test - most HMI software includes a runtime simulator, so you can test screens with a simulated PLC before going to the machine.
• Download and commission - load the project to the panel and verify every button and value on the real machine.

In our HMI and SCADA in Siemens TIA Portal and WinCC course you go through this process on real projects, from the first screen to alarms, recipes and SCADA.

Summary

HMI systems form the foundation of modern industrial automation, enabling operators to efficiently manage machines and processes. From simple button panels to advanced touch interfaces integrated with AI and IoT, HMI has evolved into an indispensable tool in every modern factory. The key aspects of effective HMI design include ergonomics, simplicity, safety, and personalization.

Today’s HMI systems, enhanced by technologies like predictive analytics, cloud computing, and augmented reality, are becoming even more efficient and user-friendly. Looking ahead, we can expect further integration of HMI with advanced technologies, driving better automation and optimization of industrial processes. This evolution will allow HMI interfaces to meet the growing demands of rapidly developing industries, offering operators an even more intuitive and secure way to control complex industrial systems.

HMI - Frequently Asked Questions

What does HMI mean in automation?

HMI means Human Machine Interface: the operator panel or software used to monitor and control a machine or process that is run by a PLC.

Is an HMI the same as a PLC?

No. The PLC executes the control program and reads inputs and outputs. The HMI is the user interface that displays data from the PLC and sends operator commands to it. Some compact devices combine both functions, but they are still two separate roles.

How do I learn HMI programming?

Start with one platform that matches the PLCs you work with, such as WinCC in TIA Portal or CODESYS Visualization. Build simple screens connected to a simulated PLC, then add alarms, trends and user management. Most HMI software has a free trial or simulator, so you can practice without hardware.

Discover more of our posts on the ControlByte blog - happy reading!