How to Program HMI-interfaces for industrial automation?

Well programmed HMI-the interface may mean the difference between the production that is running smoothly and the machine where the operator needs the help of the repairer when any malfunction occurs. Imagine a production line that suddenly stops. Only a red light appears on the screen with the inscription "Fault". What happened? Which sensor triggered the shutdown? Is there a problem with the tire, the engine or the communication?

That's why programming HMI-interfaces for industrial automation it's not just drawing buttons on the screen. It is a user interface design that allows the operator to view the machine, the technician to quickly detect errors and the manufacturing manager to better control the process.

HMI (Human Machine Interface) is a human-machine connection. It usually communicates with a programmable logic controller (PLC), which performs control logic. HMI displays data, allows parameter input, control of authorised functions and monitoring of alarms and production results.

How Programming works HMI-screen? Seven Key Steps

1. Analysis of machine and user needs. First, determine which functions the operator must operate. Does it need to start and stop, set the speed of the assembly line, monitor the temperature, display the weight or select production recipes? At this stage, we also determine what the maintainer needs to see and what the authorised person can change.
2. Selection HMI-interfaces and software. For Siemens's HMI-paneles, WinCC is often used in TIA Portal and for Weintek's, EasyBuilder Pro. The choice depends on the controller, communication protocols, screen size, required functionality and possible future upgrades.
3. Establishment of communication between HMI and PLC. HMI is connected to the controller via an appropriate industrial protocol, such as Modbus TCP, Modbus RTU, PROFINET or Ethernet/IP if supported by the selected devices. Determine IP-addresses, communication parameters and data registers. Correct data types, addressing and conversion of values into understandable measurement units are particularly important.
4. Graphical user interface design. We create transparent displays showing machine operation, control buttons, numerical values, graphs and status indicators. The operator needs to understand in a few moments whether the machine is working properly. The most important information is visible immediately and detailed settings are arranged in separate menus.
5. Programming alarms, diagnostics and recipes. In the event of an error, HMI shall display an understandable message, the cause where it can be detected by the system, and an appropriate instruction for correction. Instead of "Error 17" is more useful "The product has not reached the weighing station – check the optical sensor". We can add the history of alarms, measurement charts, product counters and storage of production settings.
6. Setting user rights. We give the operator day-to-day management, the repairman diagnostics, and the administrator access to the secure settings. Passwords, limits on permitted values and recording of significant changes reduce the possibility of unintentional interventions in production.
7. Simulation, testing and transmission of the program. Before starting, check the operation of screens, communications, alarms and commands. Specifically, we test the loss of connection, restart and incorrect entries. Next is the transmission of the program on HMI-panel, the verification on the actual machine and the production of a backup project.

Practical example: HMI for automatic balance on production line

Imagine an automatic control scale that checks the mass of products on the conveyor belt. The operator must quickly determine whether the products are within the permitted tolerances and, if necessary, select another production programme.

To HMI-screen can be displayed:

• The currently measured product weight in grams.
• Minimum and maximum permissible weight.
• Number of corresponding (OK) and non-compliant (NOK) products.
• Speed of the conveyor belt and state of propulsion.
• Status of optical sensors and ejection mechanism.
• Active alarms and error history.
• Choice of recipes for different products.
• Service menu with secure settings.

Example: The operator selects a recipe for a product with a nominal weight of 250 g and sends the tolerance of ±2 g. HMI to the required settings to the controller to verify and use them. The system shall monitor the weighing results during operation. If the product is outside the authorised range, the control logic shall carry out the intended ejection process. The HMI shall display the result and the corresponding notification.

It is important that HMI does not normally implement timing critical control or safety logic. PLC, dedicated electronics or appropriate security systems are responsible for this. In particular, HMI is a transparent and understandable management and diagnostic link to the process.

What problems are solved by quality programmed HMI?

1. Fear of expensive production stops

When the machine stops, every minute counts. The HMI shall use appropriate diagnostics to show the operator where the problem is and what to check. Instead of long speculation, the maintainer can quickly determine whether the problem is due to a sensor, engine, communication or other part of the system. This may significantly shorten the search for the cause of the error.

2. Fear of Wrong Settings

Wrongly introduced temperature, speed or tolerance may mean rejected products and unnecessary costs. Therefore, when programming HMI we set the permitted values, clearly mark the units of measurement and use additional confirmation or corresponding user rights for important changes.

3. Dependence on one programmer

Poorly documented HMI-the project may become a serious problem when the original contractor is no longer available. Therefore, it makes sense to save the original project file, document the links to the PLC, create a backup and record the software versions. Thus, future upgrades are HMI-interface and servicing significantly easier.

4. Untransparent machine management

Too many buttons, unconnected information and unclear symbols increase the possibility of error. A good industrial user interface shows the most important data on the central screen and distributes the details into transparent menus. Colors are used thoughtfully, especially for warnings and abnormal conditions.

Can Older People Program HMI-interfaces?

Yes, in many cases older HMI-panel can be repaired, adjusted or replaced by a more recent model. First, however, it is necessary to check the manufacturer, the device label, the software version, the availability of the original project and the method of communication with PLC.

If the source file is not available, it is sometimes possible to backup an existing application, but it does not necessarily allow its editing. In such a case, partial or complete reconstruction of screens and functions may be required.

How much does programming cost HMI-interface?

The price depends on the complexity of the system. A simple HMI with a few screens, basic displays and buttons requires less work than a comprehensive interface with manufacturing recipes, alarm logs, graphs, various user rights and a multi-controller connection.

In evaluating the project, we take into account the number of screens, data points, communication links, necessary macros and the scope of testing. It is also important whether we upgrade an existing machine or develop a completely new control system.

Can HMI programming be learned without prior knowledge?

You can win the basics with a simple test project. Start with one screen, digital input display, start command and display the device's current state. Then add numerical display, alarm and user rights.

More demanding projects require understanding PLC-programming, industrial communications, electrical schemes, state of the machine and safety. A beautifully designed display does not mean a reliable steering system!

How can we help you with the Black Council?

In the company Svet Črnil from Ljubljana we are also working on the development of solutions for industrial automation, robotics and machine building. In HMI-projects aim to combine technical correctness with simple management, transparent diagnostics and the possibility of further upgrading.

Whether or not you need programming new HMI-interface, HMI connection with PLC-controllers, renewal of existing displays or upgrade of industrial machinery, it makes sense to start the project by reviewing the equipment and actual production needs.

Do you have a machine with an opaque screen, recurring errors, or do you want to update control? Send us the HMI-panel label, the type of PLC-controller and a description of the desired features. Together we can check for more reliable, safer and user-friendly automation!