What Is an HMI? Operator Panel Selection Guide
An HMI is an industrial interface device that lets an operator monitor a machine on screen and control it through the PLC; this guide covers PLC compatibility, ports and screen selection.
What is an HMI and where is it used
HMI (Human Machine Interface) is an industrial interface device, usually touch-operated and mounted in an enclosure or on the machine body, through which an operator monitors and controls a machine or process on a screen. In Turkish, the same product group is also called HMI panel, operator panel and touch panel.
In most applications, the program that runs the machine runs in the PLC systems; the panel displays the values in the PLC and writes the commands and setpoints the operator enters to the PLC. Typical applications are packaging lines, pump and compressor stations, filling machines and building automation panels. Siemens describes HMI as an industrial visualization solution and notes that operator panels range from machine-level units to PC-based systems.
HMI panel types
The main products in the category are operator panels with a display; there are also two separate subcategories.
- Fixed-mount touch panels: Panels mounted by cutting an opening in the enclosure door or the front of the machine. Screen sizes are listed with values such as 4.3, 7, 10.1 and 15 inches.
- Handheld terminals: Models designed for wired portable use. Example product names include products with a handwheel, such as the Delta DOP-107HS46A.
- HMI controllers without display: HMI controllers that have no screen are listed in a separate subcategory.
- HMI accessories: Auxiliary parts used together with the panel.
What to look at when choosing an HMI
- PLC and protocol compatibility. The panel software must include the driver (communication protocol) for the PLC model you will connect to. This is checked before screen size.
- Communication ports. The number of serial ports and the Ethernet port determine how many devices you can talk to at the same time. In the category, the number of serial ports is listed as 1, 2, 3 and 4, and some models have none. If the physical interfaces of the panel and the PLC do not match, converters and gateways among the industrial communication products are also considered.
- Screen size and resolution. It is chosen according to the number of values, graphics and buttons you want to see on the screen at the same time; resolution is listed with values such as 480 × 272, 800 × 480 and 1024 × 600.
- Brightness and environment. Screen brightness is given in cd/m²; in a bright environment a higher value improves readability. Operating temperature and front panel protection rating must suit the place where the panel will be installed; the limits are taken from the product's manufacturer data.
- Memory, real-time clock and transfer ports. A clock provides time information for alarm and event logs, memory is used for logging and recipe backup, and a USB or card slot is used for transfer; this hardware varies by model. On the Delta DOP-100 series, recipes can be updated and backed up via USB disk, SD card or FTP.
- Cut-out dimensions and software. Fit to the existing enclosure cut-out is important. Each brand uses its own programming software; one brand's project file generally cannot be transferred directly to another brand's panel.
Port information in the Delta model code
On the Delta DOP-100 series, the type letter in the model code indicates the port configuration (such as the E in DOP-107EG): type B has 1 COM port, type C has 2 COM ports, type E has 2 COM ports and 1 Ethernet port, and type M has 2 COM ports and 2 Ethernet ports. The same catalog gives the front protection rating of the fixed-mount models as IP65 (for indoor use only) and the operating temperature as 0 to 50 °C; for the wired handheld terminal, IP54 and 0 to 40 °C are stated. For other brands and series, refer to the manufacturer data.
The difference between an HMI and a Panel PC
An HMI is a device programmed with its manufacturer's own software and usually focused only on visualization and control. Panel PCs, on the other hand, are computers integrated with a display; they are preferred when PC-based software such as SCADA or additional applications must run. If you only need a machine interface, consider an HMI; if additional software will be run, consider a panel PC.
Brands in this category
- Schneider Electric: Models with 10, 12 and 12.1 inch screens, such as HMIST6500, HMIET6500, HMIDT651 and HMIGTO6315.
- Delta Electronics: DOP series panels with 7, 10.1 and 12.1 inch screens, and a wired handheld terminal.
- GMT: Operator panels with 7 and 10.1 inch screens.
- ABB: CP series operator panels such as CP604-B, CP610 and CP6410.
Ordering notes
Products are sold by the piece. Some panels carry a "made to order" (terminli) label; for these products, the lead time is communicated separately before the order. You can reach a product directly by typing the full model code or stock code into the store search.
Comparison and selection table
| Selection Criterion | Compact Touch HMI (4.3" – 7") | Wide-Screen Industrial HMI (10" – 15"+) | Networked / IIoT Enabled HMI Panel |
|---|---|---|---|
| Display & Resolution | 4.3" (480×272) or 7" (800×480) TFT color LCD | 10.1" (1024×600) or 15" high-brightness display | 7" – 15" resistive or multi-touch capacitive screen |
| Communication Ports | RS232 / RS485 (Modbus RTU) + USB host/device | Dual serial (RS232/485/422) + Ethernet (Modbus TCP) | Dual Ethernet, VNC server, MQTT, OPC UA, data logging |
| Front Protection | IP65 front bezel, 24 V DC supply | IP65/IP66 front seal, recipe & trend archiving | IP65 front bezel, remote diagnostics & SQL/cloud push |
| Typical Application | Standalone packaging, dosing & cutting machines | Multi-zone process lines & multi-PLC operator desks | Remote pumping stations, HVAC & smart factory cells |
Frequently asked questions
What is the difference between an HMI and a PLC?
The PLC runs the machine's control program and manages the inputs and outputs; the HMI is the screen that lets the operator see the values in the PLC and write commands or settings. An HMI does not replace a PLC. On a machine the two work together and are connected through a communication port or Ethernet.
Is an HMI panel the same as an operator panel?
On the market, these two names are mostly used for the same product group: an industrial screen connected to the machine, through which the operator monitors and controls it. HMI is the general term of English origin, and operator panel is its Turkish equivalent. For the exact scope, you need to check the definition in the product's manufacturer catalog.
How is an HMI panel connected to a PLC?
The connection is made through the panel's serial (COM) or Ethernet port. The PLC brand's driver is selected in the panel software, and the communication parameters are matched on both sides. On the Delta DOP-100 series, the E-type model has 2 COM ports and 1 Ethernet port; determine the port to use according to the model code and the manufacturer data.
How is an HMI panel programmed?
Each manufacturer uses its own screen design software; the screens are prepared on a computer and loaded into the panel. For the DOP-100 series, Delta presents DOPSoft 4.0 software and a built-in Lua editor, as well as alarm, history log and user authorization functions. If you change brands, the screens usually have to be prepared again.
What size HMI panel should I choose?
Screen size depends on the number of values, graphics and buttons you will display at the same time, and on the operator's viewing distance. A small screen may be enough for simple machines that show few values; for multi-page or graphics-heavy screens, a larger size makes the job easier. Also check the enclosure cut-out dimensions and the resolution together.