Human Machine Interface Guide

Human machine interface, commonly abbreviated to HMI, is an interface between machine and user. While "interface" is a broad term that encompasses many technologies, such as office equipment, industrial computers, MP3 players and household appliances, HMI refers more specifically to process control systems and manufacturing. 

With an HMI, companies can increase productivity through the use of a highly user-friendly control center. 

What Is Human Machine Interface?

What is HMI software? Human machine interface products feature electronics that are necessary for controlling and signaling several types of automation equipment within industrial settings. You can find HMI products in a simple design that includes basic LED indicator screens, or you can find more complex HMI systems with a touchscreen and additional features. HMI systems need to be durable enough to withstand difficult environments. They should be able to resist dust, moisture, extreme temperatures, water and, in certain cases, exposure to hazardous chemicals.

Types of HMI Screens

What are the types of HMIs?

  • Data handler: For applications that require constant feedback from your company's system or printed production reports, the data handler is the perfect HMI. The data handler includes functions like data trending, alarm handling, data logging and recipes, and it must be large enough for visual representations, graphs and production summaries.
  • Pushbutton replacer: This HMI streamlines processes in manufacturing, putting every function of each button in one location.
  • Overseer: This HMI is beneficial when an application involves MES or SCADA. The overseer requires multiple Ethernet ports and will usually need to run Windows.

Now that you know about the three types of HMI screens, how do you select one?

How to Select an HMI

Before you make your purchase, you want to know exactly what's required of your HMI and how it can contribute to your workplace. 

  • Determine what screen size you need: Do you know what size screen you'd prefer? How much space do you have for the HMI unit? For SCADA software, screens need to be able to fit an HMI. A larger HMI will leave you with fewer screens.
  • Decide what touch type you want: Will you be able to use your application with the standard touch screen technology? Will you need to use an Elo touch interface? Decide what touch type you'd prefer or need for your application.
  • Consider whether you want an all-in-one product: Do you want an HMI that can include the screen, memory, storage and more, or would you prefer to keep your HMI and PC separate? This will depend both on the usage of the HMI and the physical treatment of the HMI. Keep the HMI separate if you anticipate you'll need to replace damaged screens.
  • Determine the resolution you need: To operate successfully, some software applications must have a certain screen resolution. You'll want to determine what resolution you need so you can choose the right HMI.

By selecting the right HMI for your workplace, you'll enhance the productivity of your company.

How Does an HMI Work?

HMIs make technologies easier to use. An HMI is judged on its usability, and its effectiveness impacts the entire system. An HMI should perform the function a user needs for a given task, allowing the user to expend less effort while improving productivity. 

An HMI should do more than present information and control functions — it should also provide users with active functions, information on system performance and feedback on results.

Human Machine Interface Applications

HMI can be used in multiple industries, such as: 

  • Pharmaceuticals
  • Manufacturing plants 
  • Food and beverage
  • Vending machines 
  • Utilities

In many of these industries, an HMI is the production line's backbone, improving operations significantly. An HMI enables data acquisition, supervisory control, enhanced stock control and control of every aspect of manufacturing lines.


Unlike a PLC alone, an HMI provides real-time feedback, sets off alarms and modifies the system without the need for reprogramming. The major advantage an HMI has over a PLC is functionality — HMIs can be used for both simple and complex tasks. The user can also design the user interface of an HMI to suit their needs. 

Advantages of HMI and Why We Need It

Why do we need HMI? For plants and facilities, there are several benefits of installing an HMI system. Below are a few of the many benefits of having an HMI system:

1. Alarms/Warnings

An HMI can allow plant operators to view alarms and locate a malfunction in the equipment, allowing them to react more quickly. Alarms can be preventive, so the operator is alerted before the system reaches an emergency level. Alarms can also track several different problems and increase productivity by optimizing manufacturing processes.

2. Reliable Messaging

For faxes, pages and more, operators can depend on HMI messaging. As an example, when a machine should be refilled because of a low fuel level, the operator will be alerted automatically.

3. Easier Overall Management of Plant

Using HMI technology, your company can also easily manage and carry out recipes. The high-quality graphics of HMI systems provide realistic views of a plant's operations so that operators can control the facility from central locations. This also helps with any security issues. Now an operator doesn'tneed to approach dangerous areas, and they can control the monitor from another location. 

4. Accurate Testing With Simulation

Plant managers can test equipment and devices easily through the use of an HMI with simulation. Testing can be achieved in the office without any piece of equipment. This function improves overall production and reduces startup time.

5. Cost Reduction

A human machine interface can reduce operating costs by replacing hundreds of selectors, pushbuttons, indicator lights and more. This means the need for extra cables, panels and consoles is also greatly reduced.

6. Improved Communications

HMI can also improve communications throughout the facility by using various types of equipment. This includes the use of:

  • Ethernet
  • Data Highway Plus
  • DDE (Dynamic Data Exchange)
  • Remote I/O
  • Serial port

Adding an HMI to a workplace benefits a facility by improving its productivity, operation and safety. Companies such as Red Lion provide a variety of HMI products (available for purchase through Carotron, Inc.) for even the most demanding industrial applications. To learn more, read about Red Lion HMI products.

Contact the Team at Carotron for Assistance

Does your company need a reliable HMI for your workplace? At Carotron, we manufacture and distribute electronic components. We offer free quotes, engineering support and free phone tech support for products that our customers purchase from us.

Contact a customer representative or engineer at Carotron, Inc. at 1-888-286-8614 if you need assistance figuring out what you need. We can review your application and offer the right components for the job.

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