HMI is an abbreviation for Human Machine Interface, also known as a human-computer interface . An HMI is the medium through which a system and a user interact and exchange information; it converts information from its internal form to a form that is acceptable to humans. HMIs exist in any field involving human-computer information exchange.
What does the HMI human-computer interface include?
Human-machine interface ( HMI) products consist of two parts: hardware and software. The hardware part includes a processor, display unit, input unit, communication interface, data storage unit, etc. Among them, the performance of the processor determines the performance level of the HMI product and is the core unit of the HMI.
Depending on the product level of the HMI, 8-bit, 16-bit, or 32-bit processors can be selected. HMI software generally consists of two parts: system software running on the HMI hardware and screen configuration software running on a PC with a Windows operating system. Users must first create a "project file" using the HMI's screen configuration software, and then download the created "project file" to the HMI's processor for execution via the serial communication port between the PC and the HMI product.
Basic Functions and Selection Criteria of HMI Human-Machine Interface Products
1) Equipment operating status display;
2) Data and text input operations, and printing output;
3) Production formula storage and equipment production data recording;
4) Simple logic and numerical operations;
5) It can connect to a network of various industrial control devices.
Selection criteria:
1) Display screen size, color, and resolution;
2) HMI processor speed performance;
3) Input method: Touchscreen or membrane keyboard;
4) Screen storage capacity: Note whether the manufacturer specifies the unit of capacity as bytes or bits;
5) Types and number of communication ports, and whether printing function is supported.
4. HMI (Human Machine Interface) Product Classification
The membrane key input HMI has a display size of less than 5.7 inches, and the screen configuration software is free; it is a basic product.
The display screen size ranges from 5.7 to 12.1 inches, and the screen configuration software is free; this is a mid-range product. The high-performance HMI (Human Machine Interface) based on a tablet PC computer, with multiple communication ports, has a display size greater than 10.4 inches, and the screen configuration software is paid; this is a high-end product.
5. How to use the human-computer interface
1) Clearly define the monitoring task requirements and select a suitable HMI product;
2) Edit the "project file" on the PC using the screen configuration software;
3) Test and save the edited "project file";
4) Connect the PC to the HMI hardware and download the "project file" to the HMI.
HMI Human-Computer Interface Design
One of the most common misunderstandings and misapplications of the ASM (Advanced Management System) guidelines when designing effective console HMIs (Human Machine Interfaces) is the overemphasis on color: simply applying a new color to all existing displays at a specific location on the console. This is generally referred to as a like-for-like HMI migration project. Some might hope that this mere color-similar project could transform the screen shown in Figure 1 into the screen shown in Figure 2. Typically, if the HMI of a distributed control system (DCS) is not a carefully designed hierarchical display based on the depth of console operator interaction, then it is a flattened DCS display system. In this system, most displays are precisely designed for detailed P&ID (Pipes and Instrument Diagram) displays. Faced with such a DCS display system, console operators typically use the DCS screen as shown in Figure 3, with each operator selecting the Level 3 device display and alarm summary screen according to their own preferences. Ideally, if the developers correctly applied the ASM guidelines in color selection and followed good screen layout principles, the migrated DCS display system may have a single Level 3 display screen that meets the ASM requirements, but the DCS HMI does not meet the ASM requirements.
Figure 1 shows the existing display before the HMI-like color replacement project was performed.
What are the requirements for ASM?
Using the ASM (Advanced Feature Management) guidelines in HMI design is not simply about converting color to grayscale, nor is it limited to using color only in alarms. In fact, the ASM guidelines advocate for the effective use of color, including appropriately specifying certain display backgrounds that are hue brighter than those vendor-supplied backgrounds in the HMI library that claim to meet the ASM guidelines. However, designing an HMI that meets ASM requirements must also adhere to other aspects, particularly regarding display type, content, navigation, and interaction. This necessitates attention to other implementation details:
Figure 2 shows the relocated display screen, which uses certain basic layout principles.
■ Based on the main operation steps, the display hierarchy is designed to conform to the operator's thinking pattern;
■ A second-level control and monitoring screen with a design and display hierarchy is used to complete daily operations;
■ In collaboration with subject matter experts, based on needs analysis, identify the display content at levels 1, 2, 3, and 4, enabling the HMI to support operator condition awareness, daily monitoring and control operations, fault diagnosis activities, and abnormal operating condition management.
■ The previous browsing strategy has been changed to a new, redesigned, hierarchical approach that utilizes simple screen browsing objectives to meet the operator's mental model and enable fast, error-free use;
■ The pop-up display screen applied to the entire display content has been replaced with window management technology, which can assign different display types to specific areas and preset sizes;
■ Provides real-time browsing of the Level 1 overview display, such as KPI and trend overview, Level 2 monitoring and control display, panel, real-time trend and alarm summary details (Figure 4), etc., instead of designing the entire HMI as a single screen, a single display system (Figure 3).
Figure 3 shows a typical console screen, which utilizes an HMI-like replacement migration project.
Figure 4 shows a conceptual diagram of a console operator HMI following ASM (Automatic Management System). In this example, through a linked navigation mode, it provides operation screens, panels, device details, real-time trend operations, and supports large-scale image-based operational status recognition.
The ASM guidelines are not simply about using gray backgrounds and restricting color usage. In the initial version, color requirements were just one of 16 guideline categories. The goal of the ASM HMI guidelines was to design an operator HMI framework that could support operator cognition and effective interaction. The second version (Bullemer & Reising, 2013) shifted the focus to the display hierarchy, its role in operator cognition, and its role as the basis for operator interaction and navigation. This shift in focus led to the removal of the word "display" from the title of the second version to emphasize the integrity and effectiveness of the console operator HMI design. Although the ASM guidelines address the design of individual display screens, the overall HMI design framework is enhanced by the requirement to use multiple display screens and interactive devices to display multiple screens at different levels of detail on the same console operator station.
The recent trend of upgrading displays to widescreen creates opportunities for direct upgrades to ASM-compliant HMIs. In particular, if the migration project abandons the typical single-screen, single-display approach, the extra pixels on a widescreen provide some space for HMI to accommodate panels, trend windows, and Level 4 displays, which would otherwise need to be displayed as pop-ups on a full-screen operating display (Figure 5).
Figure 5 shows a widescreen schematic of the console operator HMI concept following ASM, using a drop-down navigation mode in this example.
Operator's awareness
ASM's vision is for empowered operations teams to proactively manage their plants, achieving maximum safety while minimizing environmental impact and operating processes within optimal limits. Effective operator-managed HMI (Hardware Management System) design practices partially overlap with these goals: operators can proactively manage production processes, optimize plant performance, and prevent abnormal conditions. Furthermore, when abnormal conditions do occur, the aim is to enable operators to recognize the current situation, quickly bring the plant to a safe state, and then return it to normal operation.
The link between cognitive operation and the console operator HMI lies in the operator's perception of operating conditions. Ensuring operators continuously update their understanding of operating conditions, grasping the status of processes and equipment, results in appropriate control actions being taken before alarm limits are reached—this is the essence of cognitive operation. Establishing a high level of operator perception of operating conditions and providing effective operational HMI design practices is a crucial step for operating companies to achieve cognitive operation.
Figure 6 is a schematic diagram of the console operator HMI concept that follows ASM, while also supporting proactive operator situation awareness, from the big picture to the label details.
The Endsley model summarizes condition perception into three stages:
■ Perceive information and change accordingly;
■ Understand the process status and any implied deviations;
■ Predict the direction the process will take and the available response time.
In the Endsley model of working condition cognition, a key psychological component is the mental model. Rasmussen and his colleagues have demonstrated that human experts working on complex systems possess mental models that encompass different levels of abstraction and detail. They have shown that human experts move back and forth between different levels of abstraction and detail when performing assigned tasks, which can be explained by the hierarchy of knowledge about how complex systems function and the contents of the equipment.
HMIs that follow the ASM (Advanced Management Model) guidelines consciously define display types at different levels of the mental model structure to create display hierarchies that satisfy these mental models. Furthermore, as shown in Figure 5, each of these display types has a homepage in the overall HMI design, allowing operators to easily and promptly switch between information from different display types. This aligns with human factors research in mental models. Providing rich trend information interfaces also supports operators' cognitive abilities, enabling the prediction of system operation direction and speed, which is consistent with condition cognition and human factors theory in mental models.
The advantages of HMIs that meet ASM requirements have been proven. In a controlled comparison, professional petrochemical plant operators, using their plant's high-fidelity simulator, found that DCSHMIs using the ASM system approach were 41% faster in completion time, 36% more accurate in diagnosis, and 380% more effective in detecting process fluctuations before the first alarm occurred.
Recent research by the ASM organization has demonstrated the improvement in operator condition awareness achieved by using range control displays created with qualitative and overview instruments, as well as qualitative trend indicators.
HMI and effective operator interaction
Fast, error-free browsing of the display hierarchy and interaction with the DCS itself are crucial for operator performance, not to mention effective cognitive operation. HMIs compliant with ASM (Advanced Management System) provide screen browsing that reflects the overall display hierarchy and clearly shows the operator's location, key alarm conditions, and whether browsing linked through ASM best practices or the industry-standard drop-down menu style browsing has been implemented.
The ASM-compliant HMI also supports rapid operator input. For a given tag, a dedicated area on the HMI is provided to open the panel when control adjustments are needed (Figure 4). Simultaneously, the HMI also provides a dedicated area for Level 4 displays, through which operators can interact with pre-defined controllers, selectors, and indicators. These combinations may be based on cascade control loops or combinations of different Level 3 displays to support specific activities (e.g., igniting the heater pilot gas and fuel gas, operating the flow controller to support heater startup).
Operator interaction also includes window management, eliminating the need for operators to move pop-ups and panels, resize windows, or close them. Systems with sufficient tools, or even those without such tools but using minimal scripting, can eliminate the need for operators to divert their energy and attention from plant processes to window management activities.
Basic design principles
In enhancing operator capabilities to adopt proactive operational strategies, two fundamental design principles determine the effectiveness of operator HMIs, as described below:
■ The operator interface allows operators to maintain a high level of real-time awareness of the state of the processes under their control, while also allowing them to perform specific operations on individual process units and equipment at a very specific level.
■ The operator interface allows operators to focus on the process they are controlling, rather than interacting with the underlying system platform. This means that HMIs are consistent and easy to use from the perspective of understanding and interacting with process control systems with minimal console operator effort and physical resources.
When color usage is critical to supporting subsequent design principles, other ASM (Advanced Feature Management) guidelines need to be utilized to ensure that an HMI meets ASM requirements. An HMI design based on an effectively defined display hierarchy, a multi-screen/multi-window approach that allows simultaneous access to different displays within the hierarchy, and effective navigation and interaction support are also necessary to meet ASM requirements, rather than simply requiring color to indicate alarms on grayscale displays.
