HMI (Human Machine Interface) Guide

"HMI" stands for Human Machine Interface. These devices are also known as Man Machine Interface (MMI), Operator Interface Terminal (OIT), Local Operator Interface (LOI), Operator Terminal (OT), but for the purposes of this guide we will refer to them as HMIs.

An HMI is exactly what the name implies: a graphical interface that allows human users to interact with a system's machinery. As technology develops, HMIs are becoming more abundant in everyday tasks for consumers. Gas station pumps, self-service kiosks, ATM machines, and self checkout lines all use HMIs to process user inputs, convert them to machine readable code, and perform tasks without the need for an attendant, teller, or other employee. In the context of manufacturing and process control systems, an HMI provides a visual representation of the control system, and provides real time data acquisition. An HMI can increase productivity by providing a centralized display of the control process that is extremely user-friendly.

In manufacturing lines, HMIs have can monitor and control processes outside of a Central Processing Unit (CPU), and may be equipped with data recipes, event logging, video feed, and event triggering, so that users can update system processes without changing any of the hardware. For a manufacturing line to be integrated with an HMI, it must first be working with a Programmable Logic Controller (PLC) which acts as the CPU. The PLC takes the information from inputs (physical sensors or commands from the HMI) and transforms it to processes for manufacturing. While these inputs and processes are being performed, the HMI provides a display of received inputs, control process outputs, and defined user variables being leveraged to perform the tasks.

HMIs are typically used in conjunction with a PLC (Programmable Logic Controller) to monitor and control processes in an automated system. In general terms, the HMI allows the user to communicate with the PLC via a graphical interface (typically a touchscreen). This interface allows commands to be given, and also receives and translates feedback data from the PLC, which is then presented in an easily accessible visualization on the screen. This provides the operator with much-needed flexibility and control over a given system. An excellent example of a common HMI would be a tablet or smartphone, which have built-in touchscreens that allow users to interact directly with the machine's programming.

HMI products were originally designed to meet the need for easily operational machinery, while producing optimal outputs. Predecessors of the HMI include the Batch Interface (1945-1968), Command-Line User Interface (1969-Present), and the Graphical User Interface (1981-Present).

The Batch Interface was a non-interactive user interface, where the user specified the details to the batch process in advance, and received the output when all the processing was done. This batch process did not allow for additional input once the process has begun, making them much less agile than HMIs used in modern manufacturing lines.

The Command-Line Interface was a mechanism that interacted with a computer operating system or software by typing commands to perform specific tasks. The concept of the Command-Line interface originated when teletypewriter machines were connected to computers in the 1950s, and offered results on demand; this feature was ultimately the downfall of Batch Interface, which was unable to deliver results on demand. A basic example of Command-Line Interface would be windows Disk Operating System "DOS" which dominated the 1980's.

Over time, interfaces became increasingly complex and easier to use. One such interface would be the Graphical User Interface (GUI), which allows people to interact with programs in a more visual manner, such as via symbols on touch screens rather than text commands.

The modern HMI stems directly from the Graphical User Interface, and comes from the need to control and operate machinery much more effectively. Human Machine Interfaces, formerly known as Man Machine Interfaces, are now leading the way in the control of manufacturing processes as extremely user-friendly devices.

The greatest advantage of an HMI is the user-friendliness of the graphical interface. The graphical interface contains color coding that allows for easy identification (for example: red for trouble), as well as pictures and icons which allow for fast recognition, easing the problems of language barriers.

Because HMIs increase system efficiency, they can reduce production costs, which could potentially increase profit margins. Modern HMI devices are extremely innovative, capable of higher capacity and more interactive, elaborate functions than ever before. Some technological advantages the HMI offers include converting hardware to software, eliminating the need for mouse and keyboard, and allowing kinesthetic computer/human interaction.

• Advantages of an HMI over a PLC alone

  A PLC on its own cannot provide any real-time feedback, and cannot set off alarms nor modify the system without reprogramming the PLC. The key advantage to an HMI is its functionality; an HMI can be used for simple tasks such as a coffee brewing controller, or as the sophisticated control unit of a nuclear plant. With new HMI designs emerging in the field, we are now seeing HMIs that offer remote access, allowing operators access to the terminal from a distance. Another advantage of an HMI is its customizability. The user can personalize the user interface for maximum ease-of-use.

• Convenience

  The convenience that comes with an HMI is invaluable, and the functionality achieved by digitizing a system with an HMI is unbeatable. An HMI combines all of the control features typically found throughout the automation line and places them in one centralized, remotely accessible location, eliminating the need, for example, to run to a red pushbutton to stop the production line in case of an emergency. With remote access, the operator does not need to be near the automation line to start, stop, or monitor production. The operator can access all the same controls on a centralized unit in a compact form. Simplicity is also a big factor in the usability of an HMI. The screens and functions provide for ease-of-use to supervise the automation line.

• Interface Flexibility

  One of the most valuable features of an HMI is the ability to personalize the interface. An HMI can fully support the most complex applications, with multiple screens and several routines running. If the user is looking to program an HMI with something more simplistic, they may write instructions for the controller directly into the HMI. Every HMI comes with different features: some may play sound or video, while others offer remote access control. The design of the user interface should be optimized for specific applications, taking into consideration all the capabilities of the typical user, as well as the environmental aspects such as noise, lighting, dust, vision and technological curves.

There are three basic types of HMIs: the pushbutton replacer, the data handler, and the overseer.

• The Pushbutton Replacer

  Before the HMI came into existence, a control might consist of hundreds of pushbuttons and LEDs performing different operations. The pushbutton replacer HMI has streamlined manufacturing processes, centralizing all the functions of each button into one location. The pushbutton replacer takes the place of LEDs, On/Off buttons, switches, or any mechanical device that performs a control function. The elimination of these mechanical devices is possible because the HMI provides a visual representation of all these devices on its LCD screen, while performing all the same functions.

• The Data Handler

  The data handler is perfect for applications requiring constant feedback from the system, or printouts of the production reports. With the data handler, you must ensure the HMI screen is big enough to display information such as graphs, visual representations of data, and production summaries. The data handler includes such functions as recipes, data trending, data logging and alarm handling/logging. The data handler is used for applications that require constant feedback and monitoring. Often these data handlers come equipped with large capacity memories.

• The Overseer

  Anytime an application involves SCADA or MES, an overseer HMI is extremely beneficial. The overseer HMI will most likely require Windows to operate, and have several Ethernet ports. The overseer works with SCADA and MES. These are centralized systems that monitor and control entire sites or complexes of large systems spread out over large areas. An HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information.

All HMIs have a processor, and memory. It is important to make sure that the processor and memory capabilities are sufficient enough to control a given system.

Additional physical properties of an HMI vary from model to model, application to application, and among manufacturers. An HMI that is located in a water plant might have various water seals around its perimeter, as opposed to an HMI that is located in a pharmaceutical warehouse which would not require waterproofing.

The size of an HMI is also a key physical property that will vary, because not all applications require a large, high-resolution monitor. Some applications may only require a small, black and white touch screen monitor. When it comes to selecting an HMI, the physical properties are extremely important because one must take into consideration the operating environment, and what safety measures the HMI needs to protect itself. Also, a specific size may be needed due to space limitations.

An HMI is a substantial purchase, so it is important to know exactly what is required of it. HMIs typically perform one of three primary roles: a pushbutton replacer, a data handler, or an overseer. The pushbutton replacer HMI takes the place of LEDs, On/Off buttons, switches, or any mechanical device that performs a control function. The Data Handler is used for applications that require constant feedback and monitoring. Often, these data handlers come equipped with large capacity memories. The overseer works with SCADA and MES, centralized systems that monitor and control entire sites or complexes of large systems spread out over large areas. An overseer HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information.

First consider the other components that are necessary to make a manufacturing control system operate. The production line consists of all the machinery that performs the work required in the production of the product. Next, consider the various input/output sensors that monitor temperature, speed, pressure, weight and feed rate. Third, decide on the programmable logic controller (PLC) that will receive the data from the input/output sensors, and converts the data into logical combinations.

Select an HMI based on the needs of the system. HMIs are initially separated by their display size; typically spanning from 4.3” up to 15” diagonal. Within these sizes, HMIs are separated by their characteristics, namely their communication capabilities. HMIs with multiple COM and/or Ethernet ports will usually be more costly, but will allow for an overseer type application to be well connected to multiple PLCs. Make sure that the communication protocol your PLC uses can connect to the HMI by first verifying the protocol of the PLC and ensuring it exists on the HMI Communications and Connections Guide.

If you have a system that has many very simple and repeatable processes, you may not need an HMI with a large memory capacity. In this instance, you can choose an HMI based on size and choose one with the appropriate price point.

Environmental Considerations for an HMI

Which HMI Programming Software to Choose?

Wiring an HMI

HMI Applications

HMIs are used throughout various industries including manufacturing plants, vending machines, food and beverage, pharmaceuticals, and utilities, among many other applications. HMIs, along with PLCs, are typically the backbone of the production line in these industries. The integration of the HMI into any manufacturing system can vastly improve operations. The HMI allows for supervisory control and data acquisition in the entire system, so parameter changes are available at the operator's choosing.

For example

An HMI also offers improved stock control and replenishment, meaning fewer replenishment orders are required of the vendors. Utility companies may use HMIs to monitor water distribution and waste water treatment.

HMI Troubleshooting

HMI Glossary