Some info about Human Machine Interface displays…

Lets have a fun little discussion about Human Machine Interface.
The discussion will be a general overview and will assume no previous knowledge about the subject.
This discussion will also be from the point of view of a person working in the maintenance department of a manufacturing facility, specializing in electrical and control issues.
And that would be me, Your friendly, faithful and ever vigilant administrator here at

I have already done a piece about PLC’s (Programmable Logic Controllers) on this website, so for those of you who are unfamiliar I would suggest reading that first.

Typical HMI

An HMI is a touchscreen mounted in an area industrial activity.
The purpose is to allow operator control of manufacturing equipment and provide feedback concerning the process status back to the operator.

The HMI works in conjunction with a PLC, passing information to and receiving information from the PLC,( or multiple PLC’s) through a communications network.
In modern times this network is a propriety, and derived from standard Ethernet. This industrial network will typically be populated with things like PLC,s, Motor controllers, HMI’s, etc.
This is a good place to state that industrial Ethernet networks are usually separated from normal office type Ethernet networks. Although sometimes gateways are provided to get from one network to the other.

So how does one program such a wonderfully productive beast?
I’m glad you asked!
Like PLC’s, propriety software created by the equipment manufacturer is typically needed.
This software runs in the programmers computer and provides the means of both creating the user program, and of downloading the user program to the HMI, so that it can start it’s glorious career of helping humanity create useful things.

And now, let’s focus on the actual practice of creating the User program and downloading it to the HMI.
Drum-roll please…

Typical screen

Once the programming software is fired up on your desktop and you are programming within a display screen you have created, there will be many graphical components available to you to place in your new display.
Options of size , color and position within the display are yours for the taking.
Some of these graphics components are for Control,others are for condition indication, and still others provide navigation amoungst different screens you may have created.
Some control components might include momentary push button, latched push button, numeric input,ramp buttons, and control list selectors.
Some display(condition feedback) components might include numeric display,local message display, time and date display, also conditions could be indicated through color manipulation of any object. You can even import your own images to use for control or indication purposes.
Other possibilities include navigation buttons through different displays.
Most programs contain multiple screens, each dedicated to different subjects such as tasks or areas of a machine.

Once the graphics and screens have been created, it is time to concern ourselves with communication.
As indicated previously, full communication between the PLC and HMI is necessary.
each object in the HMI program can be bound to a specific object within the PLC program, usually by right clicking the object in the HMI programming software (which brings up all options for that object).

Once you are done creating the HMI program and referenced all graphical objects to elements within the PLC program, it’s time to download your program to the HMI display using your programming computer and either a communications cable or the network.
Once a push button (for instance) is bound to a unique element within the PLC program, and the button is pushed on the HMI(after downloading), something is going to happen, what that is depends on what that bound element is doing within the PLC program.

Some Manufacturers hmi pages:

I hope this satisfies any curious desire for information.

Wayne Dover,


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