In this article you will learn all about HMIs. You may never have heard of HMI, but I bet you meet them regularly. HMI is short with Human Machine Interface. We use HMIs in the industry to control and monitor equipment. The most common HMI you come across on a regular basis would be an ATM machine. The screen and buttons allow you to use the machine to withdraw a certain amount of money, or to deposit money. Let’s talk about industrial HMI now.

It can be difficult to find a good automated process in the industry without HMI. Most of the time HMI will be in the form of a screen, similar to a computer screen, and more often than not, it is a touch screen. The operator or maintenance staff can operate and monitor the machine from HMI. They can include details such as temperature, pressure, process steps, and calculation. They can also show very accurate levels in tanks and the exact position of the equipment. Where machine information used to view multiple indexes can now be viewed on a single screen. Opportunities are limited only to the software and hardware used.

For maintenance personnel, most HMIs can reconnect to the PLC concept and display it on screen for problem-solving purposes. This can save you valuable time compared to connecting a computer or laptop regularly. Another advantage of having modern HMI is the fact that plants and other industrial sites can monitor and control many machines or other equipment. A small production facility can monitor the entire plant in one central HMI.

Water and wastewater sources have used this for years by combining HMI and PLC. They can monitor remote locations, such as water pumps, and equipment inside the plant. You are probably getting the idea now as HMI is a performance panel with a monitoring screen. But how does HMI actually connect to a machine so that it can control and monitor it? Let’s take a look.

HMI requirements?

First of all, HMI uses special software so that engineers can better configure it. Different types of panels use different software accordingly. The software allows the engineer to design what the operators will actually see on the screen, what they can monitor on the screen, what “buttons” can be pressed and how the operator can control the machine. For example, HMI may have a large tank displayed on the screen at the displayed liquid level. Next to the tank is a pump to lower the liquid level. HMI can have a start and stop button displayed and operated on the screen next to the pump. This mirror will be able to turn on and off the pump. However, it is not as easy as simply putting a button on a screen or a level tank on the screen.

The HMI programmer must set each indicator and button at a specific input or output address of the PLC. This raises another point, HMI and PLC need to be compatible. This means that they need to be able to “talk” to each other. They do this in what is called the Protocol. Different companies use different agreements. Common protocols are Modbus, Ethernet / IP, and Profibus. These are just industrial networks, similar to the network you can have in your home with multiple computers, TVs or other devices connected to each other. Industrial agreements connect different PLCs, HMIs, and other equipment to each other.

Protocol details are readily available on each manufacturer’s website. If PLC and HMI are “talking” then anything included in HMI can be used to monitor and control PLC activities.


Let’s review, today you learned some of the basics of HMI or Human Machine Interface. These are machine monitors and controls that allow the operator to operate the machine or monitor the machine. Engineers can configure HMI to perform almost any unregulated work or details that can be monitored by PLC. HMI and PLCs work together to monitor and control the machine. This means that they have to get along and they have to speak the same language in order to speak. This comes in the form of a Protocol that is just an industrial network.

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