What is an HMI?

HMI is the acronym for Human Machine Interface, and can be designed as just that; an interface between the user and the machine. An HMI is considered an interface; a very broad term that can include MP3 players, industrial computers, household appliances, and office equipment. However, an HMI is much more specific to manufacturing and process control systems. An HMI provides a visual representation of a control system and provides real time data acquisition. An HMI can increase productivity by having a centralized control center that is extremely user-friendly.

HMI Block Diagram


hmi block diagram

A Human Machine Interface (HMI) is exactly what the name implies; a graphical interface that allows humans and machines to interact. Human machine interfaces vary widely, from control panels for nuclear power plants, to the screen on an iPhone. However, for this discussion we are referring to an HMI control panel for manufacturing-type processes. An HMI is the centralized control unit for manufacturing lines, equipped with Data Recipes, event logging, video feed, and event triggering, so that one may access the system at any moment for any purpose. For a manufacturing line to be integrated with an HMI, it must first be working with a Programmable Logic Controller (PLC). It is the PLC that takes the information from the sensors, and transforms it to Boolean algebra, so the HMI can decipher and make decisions.

Basic Types of HMIs

FamilyShot HMI

There are three basic types of HMIs: the pushbutton replacer, the data handler, and the overseer. 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 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 for such things as graphs, visual representations and production summaries. The data handler includes such functions as recipes, data trending, data logging and alarm handling/logging. Finally, anytime an application involves SCADA or MES, an overseer HMI is extremely beneficial. The overseer HMI will most likely need to run Windows, and have several Ethernet ports.

How to Select an HMI

An HMI is a substantial purchase, so it is important to know exactly what is required of it. An HMI is used for three primary roles: a pushbutton replacer, data handler, and overseer. 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 can provide a visual representation of all these devices on its LCD screen, while performing all the same functions. The Data Handler is used for applications that require constant feedback and monitoring. Often these Data Handlers come equipped with large capacity memories. The last of the HMI three types is referred to as the overseer, because it 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.

Physical Properties of a HMI


The actual physical properties of an HMI vary from model to model and among manufacturers. It is important that one makes the appropriate selection. 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. The actual 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. Lastly, physical properties include the processor and memory of the HMI. It is important to make sure that the processor and memory capabilities are sufficient enough to control a system.

How does an HMI Work?

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.

Environmental Aspects for an HMI

The operating environment should always be considered when selecting an HMI. For example: for use in a warehouse that has excessive noise or vibration, one might decide on a heavy-duty HMI. If used in the food processing industry or somewhere that might need to be washed down, select a water-protected HMI. One must also consider temperature as a factor in the selection process. If used in a steel plant, next to a furnace, one would want something that can withstand extreme temperatures.

What Programming Software to Choose?

When considering which programming software to use, there are three main categories to choose from: proprietary, hardware independent and open software. Proprietary software is the software that the manufacturer provides, which is typically easy to use and allows for quick development. The drawback is that proprietary software will only run on that specific hardware platform. Hardware-independent software is third party software developed to program on several different types of HMIs. This type of software gives the developer much more freedom for the HMI selection. The downside to hardware independent software is that it is not as user-friendly as the proprietary. Open Software should only be selected by the advanced programmer. It allows the developer to have complete openness in the design process.

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HMI Applications

The HMI is used throughout various industries including manufacturing plants, vending machines, food and beverage, pharmaceuticals, and utilities, just to name a few. HMIs along with PLCs are typically the backbone of the production line in these industries. The integration of the HMI into manufacturing has vastly improved operations. The HMI allows for supervisory control and data acquisition in the entire system, so parameter changes are feasible as the operator’s choosing. For example, in metals manufacturing, an HMI might control how metal is cut and folded, and how fast to do so. An HMI offers improved stock control and replenishment, so the fewer journeys are required out to the vendors. HMIs are used in bottling processes to control all aspects of the manufacturing line, such as speed, efficiency, error detection and error correction. Utility companies may use HMIs to monitor water distribution and waste water treatment.

Advantages of an HMI

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). Pictures and icons allow for fast recognition, easing the problems of illiteracy. HMI can reduce the cost of product manufacturing, and potentially increase profit margins and lower production costs. HMI devices are now extremely innovative and capable of higher capacity and more interactive, elaborate functions than ever before. Some technological advantages the HMI offers are: converting hardware to software, eliminating the need for mouse and keyboard, and allowing kinesthetic computer/human interaction.

Advantage of an HMI over a PLC alone

The advantage to using an HMI over using just a PLC is the fact that there are no disadvantages! Using just a PLC will not provide any real-time feedback, cannot set off alarms nor modify the system without reprogramming the PLC. The key advantage to an HMI is it functionality; an HMI can be used for simple tasks such as a coffee brewing controller, or a sophisticated control unit of a nuclear plant. With new HMI designs emerging every day, we are now seeing HMIs that offer remote access, allowing for access of the terminal while away. Another advantage of an HMI is that the user can personally design the user interface.


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The convenience that comes with an HMI is extremely valuable; the functionality achieved with digitizing a system with an HMI is unbeatable. HMI combines all the control features that are typically found throughout the automation line and places them in one centralized location, eliminating the need to run to a red pushbutton that will stop your line in an emergency. With remote access, the operator does not need to be anywhere near the automation line to start/stop or monitor production. With remote access, the operator can have all the same features, on your centralized unit in a smaller compact form. Simplicity is also a big factor in the usability of an HMI. The screens and functions provide for easy training to supervise the automation line.

Interface Flexibility

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One of the most convenient 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, he/she can have instructions for the controller directly written onto the HMI. Every HMI comes with different features; some may play sound, play video, or even may have remote access control. The design of the actual 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.

HMI/PLC Combination

How can a PLC be controlled without ladder logic? How does an HMI replace the standard software a PLC comes with? Ladder logic is simply conditional programming. For example, if input 1 is energized, then coil 1 will be powered. A statement has to be true for the output to be executed. The same can be achieved with C programming. However, in order to program an HMI to operate a PLC properly, all the registers of the PLC must be known. A good way to learn how to program a PLC via an HMI is to first start working with the PLC and the software it came with. This helps build an understanding of how to operate the PLC without the HMI. That knowledge will easily transfer over when the user is ready to connect the two units together.


Wiring an HMI into a system may be an easy task if a PLC is already being used. This connection is as simple as connecting a USB, RS-232, RS-485 between the HMI and PLC. In some instances, both units are equipped with wireless features, making the connection even easier. Although the wiring between the PLC and HMI may be an easy task, the wiring between the PLC and the actual automation line could be chaotic. Depending on the size and complexity of the application, profibus extensions may be required for the PLC. A profibus extension is similar to a power strip that extends one input/output to multiple input/outputs by connecting to the expansion port of the PLC. A wiring schematic from the production line to the PLC is highly recommended, so that programming the HMI is sped up drastically.


Sometimes when the PLC and HMI are hooked up together and operating under the EV5000 software, a PLC error may appear. To troubleshoot the error, simply use a numeric display and set it to the PLC register the data is being written to. If this PLC register comes back with random register values, this indicates that the HMI did not deliver the information to that register. If it was sent correctly, then the numeric displays should show the information that was sent. This is a very simplistic way of solving HMI/PLC errors. See Anaheim Automation’s Video Tutorials for more help with programming an HMI.

History of the HMI

HMI products originated from the need to make machinery easier to operate, while producing optimal outputs. Predecessors of HMI include the
GP-S057web Batch Interface (1945-1968), Command-Line User Interface (1969-Present), and the Graphical User Interface (1981-Present). The Batch Interface is a non-interactive user interface, where the user specifies the details to the batch process in advance, and receives the output when all the processing is done. This batch process does not allow for additional input once the process has begun, is problematic in modern manufacturing lines. The Command-Line Interface is a mechanism that interacts 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; a big downfall of Batch Interface because it could not 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 highly complex and extremely easy to use. One such interface would be the Graphical User Interface (GUI). Graphical User Interface allows people to interact with programs in more ways than typing, such as computers, hand-held devices such as MP3 Players, Portable Media Players or Gaming devices, household appliances, and office equipment with images, rather than text commands. Human Machine Interface stems directly from Graphical User Interface, and comes from the need to control and operate machinery much more effectively. Human Machine Interface formerly known as Man Machine Interface, is now leading the way in the control of manufacturing processes as an extremely user-friendly device.

HMI Quiz

What does HMI stand for?
Human Machine Interface

How many different HMI types are currently offered by Anaheim Automation and what are the major differences?
With just Kinco, Anaheim Automation offers three different types of HMI starting with the MT4000, ranging in sizes from; 4.3″ to 12.1,” with a 400 MHz processor. The MT5020 and MT6000 on the other hand, both contain a 520 MHz processor. The MT5020 series comes standard with Ethernet capabilities along with more ports than the MT4000. The MT6000 is the complete package, although it has the same processing power as the MT5020. This HMI comes standard with Windows CE and its own SDK, which allows the user to use any programming language to build an application.

What are the benefits of using both an HMI and PLC, as opposed to just a PLC?
The benefits of using an HMI along with a PLC are substantial. PLCs tend to be complex, with many wires connected to them, making it difficult to find the correct input to manually toggle. With an HMI, the user can toggle PLC’s through memory, as opposed to having to re-wire. HMIs also provide a real time view of the system, so if recipe memory in the PLC was to max out, the user could easily wipe its contents without having to disconnect the PLC.

What is a Baud Rate?
Baud, synonymous to symbols per second, or pulses per second, is often times referred to as the unit of the symbol rate. It is the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a line code.

What communication protocols are applicable to our HMI line?

Which PLC unit do I select if my PLC is not listed under compatible PLC’s?
Selecting a PLC depends on what protocol this PLC or controller uses. If the controller uses Modbus RTU, then the user should select Modbus RTU Slave. If the controller uses ASCII, then the user should select the Universal ASCII slave.

What is Windows CE and what is the Codesy’s packet?
Windows CE in an embedded operating system, which translate to a very stripped and minimalistic copy of windows for smaller devices such as HMIs and cellular phones. The Codesy’s packet is a proprietary third party software, which will give allow the user to program an HMI and PLC.

What type of touch panel do these Kinco HMI’s use?
TFT, which stands for Thin Film Transistor

How many controllers can I hook up to one HMI?
As many COM ports as that specific HMI has.

What programming language comes standard with the EV5000?


Do HMIs have printing capabilities?
It varies depending on the manufacturer. Some HMIs will come with specific printers that are compatible, while others will not have printing capabilities. Some HMIs have the capability to install the user’s own drivers for the printer of choice.

How does one program an HMI?
There are a few third party programs that can be used to create an HMI graphical user interface, such as CodeSys and EV5000. Some HMIs come standard with their own proprietary software, which provides the functions specific to that HMI. Lastly, some HMI’s come with SDK packages so the user can program the HMI in his/her native language.

What does an HMI do?
With an HMI the user will have a centralized unit of control, which allows for decisions based on real time events in a visual manner. That HMI must be in constant communication with a controller so the HMI can receive real time data from controller. The HMI accesses specific registers on the controller and makes decisions based on the state of those registers. Most controllers deal with heavy wiring, and without a user interface they require manual input (wiring) to toggle certain registers. This is accomplished through software and makes the application simple and easy to perform.

How does the HMI communicate with other devices?
The HMI must be connected to a device, whether it is through Ethernet (RJ45), serial communication (RS232, USB or RS422), or wireless. The two devices baud rates must be in sync, so that no miscommunication occurs.

What if my Controller is not supported by this HMI?
If the software that came with the HMI does not have a universal controller option, then third-party software may be used. Most software has a generic universal controller, in case the controller being used is not considered compatible with the HMI.

What are the benefits of an HMI over a desktop?
An added benefit of an HMI is that it is application-specific. In other words, a panel will not allow for internet browsing, solitaire game play, or update reminders unless it pertains to the task at hand. HMIs provide absolute control; meaning that you may give the user limited access to specific features, or full access depending on how the interfaces are created. (See Advantages of an HMI).

HMI Glossary

Macro: Macro instructions are an advanced touch screen control method. Macro strengthens the functions of the touch screen, so it has the same logic and arithmetic operations as the PLC. The use of macros will enable the touch screen to implement many powerful functions that cannot be supported by regular components, perfecting the human-machine interface.

Recipe: A recipe activates data transmission of consecutive registers, and supports downloading data from the memory of the recipe card to the PLC, and vice versa.

LW: A local word register is a 32-bit register which has been declared within the scope of the program.

LB: A local bit register is just a 1-bit register which has been declared within the scope of the program.

RW: A recipe word register is a 32-bit register that will execute sequentially when activated.

TFT: A thin film transistor is an LCD that uses thin film transistors technology to improve image quality.