HMI Touchscreen Panel Symbol
Definition: The HMI Touchscreen Panel symbol represents a human-machine interface display unit — a touchscreen or keypad-based operator terminal connected to a PLC, controller, or SCADA system — shown in electrical and control system schematics as a rectangular block with Power, RS232, and Ethernet connection points, consistent with IEC 81346-2 functional block diagram conventions for operator interface devices.
Also known as: HMI, operator panel, operator interface terminal (OIT), operator interface unit (OIU), industrial touchscreen, Simatic HMI, GOT panel, Weintek HMI.
What the HMI Touchscreen Panel symbol means
The HMI Touchscreen Panel symbol denotes an operator interface device that provides a graphical display and touch- or button-based input mechanism allowing plant operators to monitor process variables, adjust setpoints, acknowledge alarms, and control equipment connected to a PLC or DCS. In a control system wiring diagram, the HMI symbol sits between the operator and the control hardware, communicating via serial (RS232/RS485/Profibus) or Ethernet (EtherNet/IP, PROFINET, Modbus TCP) links.
HMI panels replace traditional banks of pilot lights, analog meters, and physical selector switches with a single configurable touchscreen interface. The symbol in a wiring or control panel diagram shows the HMI's power supply connection and communication ports, allowing panel builders and engineers to understand the device's physical and electrical integration points within the control cabinet.
How to identify the HMI Touchscreen Panel symbol
The HMI touchscreen panel symbol is drawn as a tall rectangle (portrait orientation) representing the panel enclosure, with a rectangular screen area shown inside. Three terminals emerge from the bottom: Power (supply voltage input), RS232 (serial communication port), and Ethernet (network port). Some symbol representations include a simplified screen graphic or a text label such as 'HMI' or 'OP' inside the rectangle body.
Function in a circuit
An HMI touchscreen panel acquires real-time data from a connected PLC or controller via its communication port, renders process graphics, trends, and alarm lists on the screen, and forwards operator inputs (setpoint changes, command buttons) back to the controller. It acts as both a display server and a command terminal: the Ethernet or RS232 link exchanges tag data with the PLC at scan rates typically between 100 ms and 1 s, while the power supply (24 V DC or 120/240 V AC) energises the display and processor board.
Standards: IEC vs ANSI
| IEC 60617 | IEC 81346-2 defines reference designation classes for human interface devices; HMI panels fall under class S (switching/sensing devices) or P (protection/measuring devices) depending on the manufacturer's interpretation. IEC 61131-3 governs the PLC programming environment that the HMI communicates with. Graphical block representation follows IEC 60617 functional block conventions. |
|---|---|
| ANSI/IEEE 315 | ANSI/IEEE 315-1975 does not define a unique symbol for HMI panels (as the standard predates modern industrial HMIs); in ANSI-based control drawings, an HMI is represented as a rectangular functional block with labelled communication and power terminals. The designator HMI or OP (operator panel) is used. |
| Key difference | IEC and ANSI/IEEE drawings both use labelled rectangular blocks for HMI panels. IEC 81346-based drawings use systematic reference designators (e.g., =Plant+Cabinet-HMI1), while ANSI drawings typically use simpler tags (HMI1, OP1). There is no unique glyph difference between the two standards. |
Terminals / pins
| Pin | Name |
|---|---|
| power | Power |
| rs232 | RS232 |
| eth | Ethernet |
Typical values
Supply voltage: 24 V DC (most industrial HMIs) or 100–240 V AC (panel-mount models). Power consumption: 5–30 W. Screen size: 4.3 in to 21.5 in diagonal. Communication protocols: RS232, RS485, Profibus DP, EtherNet/IP, PROFINET, Modbus RTU/TCP, CANopen. Operating temperature: 0–55 °C. IP rating: IP65 (front bezel, flush-mounted).
Where the HMI Touchscreen Panel symbol is used
- Manufacturing process control: HMI panel mounted on control cabinet door displays conveyor speed, motor status, temperature setpoints, and production counts for a packaging line
- Water and wastewater treatment: operator panel shows pump run status, tank levels, flow rates, and allows operators to start/stop pumps and adjust PID setpoints
- Building automation and HVAC: HMI touchscreen on a mechanical room panel displays chiller, AHU, and VAV status, allows setpoint adjustment and alarm acknowledgement
- Food and beverage production: HMI panel provides recipe management, batch tracking, and CIP (clean-in-place) sequence initiation with sanitary stainless-steel enclosure variants
- Oil and gas remote terminal units (RTU): HMI at wellhead or compressor station shows process pressures, temperatures, and flow measurements for local operator access
- Power distribution switchgear: HMI panel on medium-voltage switchboard provides metering, protection relay settings, and breaker status for substation operators
Example
In a bottling plant control panel wiring diagram, an HMI touchscreen panel symbol (24 V DC powered via the Power terminal) is connected via its RS232 terminal to a PLC serial port (COM1) and via its Ethernet terminal to the plant SCADA network switch. The HMI displays fill-level setpoints, conveyor speed, and bottle-count totals, and allows the operator to start/stop the filling sequence.
Key facts
- The HMI Touchscreen Panel symbol has three connection points: Power (24 V DC supply), RS232 (serial PLC communication), and Ethernet (network/SCADA communication).
- HMI panels communicate with PLCs using industrial protocols including Modbus RTU (RS232/RS485), PROFINET (Ethernet), EtherNet/IP, and Profibus DP, depending on the PLC platform.
- Most industrial HMI panels are powered by 24 V DC, sourced from the control panel's 24 V DC power supply bus, and draw 5–30 W depending on screen size.
- IEC 81346-2 governs reference designation of HMI devices in industrial control system documentation; ANSI/IEEE 315 uses the designators HMI or OP for operator interface panels.
- The front bezel of a panel-mount HMI is typically rated IP65 (dust-tight and water-jet resistant) to withstand industrial wash-down environments when flush-mounted in a steel enclosure.
- HMI screens range from 4.3 inches to 21.5 inches diagonal; larger screens are used for complex process overview graphics, while smaller screens are used for simple machine interfaces with basic status and setpoint entry.
- Modern HMI panels can serve as thin clients connecting to SCADA server tag databases over Ethernet, eliminating the need for local screen programming by rendering server-side graphics.
- Common HMI manufacturers include Siemens (Simatic HMI / KTP series), Mitsubishi (GOT series), Weintek (cMT/MT series), Schneider Electric (Magelis/Harmony), and Rockwell Automation (PanelView).
Frequently asked questions
What does the HMI panel symbol mean in a wiring diagram?
The HMI panel symbol represents a human-machine interface touchscreen terminal that displays process data and accepts operator inputs for a connected PLC or control system. In a wiring diagram it shows the device's power supply connection and communication ports (RS232 and Ethernet), indicating how the panel is physically integrated into the control cabinet.
What does the HMI touchscreen panel symbol look like?
The HMI touchscreen panel symbol is a tall rectangle representing the panel enclosure, often with a smaller rectangle inside depicting the screen area. Three terminals extend from the bottom: Power (DC supply), RS232 (serial port), and Ethernet (network port). The rectangle may be labelled 'HMI' or 'OP' to identify the device type.
What voltage does an HMI panel require?
Most industrial HMI panels require a 24 V DC supply, typically drawn from the control panel's 24 V DC power supply bus. Some panel-mount HMI models accept 100–240 V AC directly, but 24 V DC is the predominant industrial standard for compatibility with PLC I/O and relay output modules.
What communication protocols do HMI panels use?
HMI panels communicate with PLCs and controllers via Modbus RTU (RS232 or RS485), PROFINET (Ethernet), EtherNet/IP, Profibus DP, and CANopen, depending on the PLC platform. The RS232 terminal on the HMI symbol represents the legacy serial port, while the Ethernet terminal supports modern high-speed industrial Ethernet protocols.
What standard defines the HMI panel symbol?
IEC 81346-2 defines the reference designation system for HMI devices in industrial control documentation. IEC 60617 functional block conventions define the rectangular block representation. ANSI/IEEE 315-1975 uses similar rectangular blocks for operator interface devices, designated HMI or OP in North American control drawings.
What is the IP rating of an industrial HMI panel?
The front bezel of a panel-mount industrial HMI is typically rated IP65 (per IEC 60529) when flush-mounted in a steel enclosure, meaning it is dust-tight and protected against water jets from any direction. This rating makes IP65 HMIs suitable for food and beverage, pharmaceutical, and industrial wash-down environments.
What is the difference between an HMI and a SCADA system?
An HMI (human-machine interface) panel is a local operator terminal — a touchscreen at a machine or control cabinet — that communicates directly with one or a few PLCs to display and control that specific equipment. A SCADA (supervisory control and data acquisition) system is a centralised software platform that aggregates data from many PLCs and HMIs across a plant or facility, providing supervisory monitoring, historical data logging, and alarm management at a higher level.
Place the HMI Touchscreen Panel symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.