HMI – Human Machine Interface

The human machine interface is a panel or screen with the information in real time from the equipment gathered by the SCADA system.
In this panel there is displays, buttons, gauges, leds and several objects to read and control a device or equipment distributed in the factory.
The HMI can be developed inside an SCADA software or in specific devices made specifically to it.
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Examples of elements in the SCADA HMI:

Buttons: Used to receive a user command. By clicking on the button, an action is triggered. Information sent to the PLC, change of HMI panel or report generation. These buttons may be hotspots distributed over a picture on the HMI in a SCADA system.

LEDs: color indicators for digital states. If a digital variable of the PLC is connected, value 1, then the color referring to the connected state is activated in a LED.

Gauge: pointer indicator for analog SCADA system variables. The minimum and maximum values of the scale are set. Limits may also be placed.

Level: Level indicators with scale. They can be used from liquid indications such as in tanks to simple scales of analog numbers. The minimum and maximum values of the scale are defined. SCADA system alarm and safety limits can also be set.

Check: key switches on and off. They are associated with digital tags. When the user clicks the SCADA HMI on the check a digital signal is sent to the PLC.

Text/number input: Components for number or text entry. Usually used in analog variables. The user enters the value in HMI and sends the variable to the PLC. Combos can also be used to stop preset values. Text may be used as information also, for example, product name.

Chart: Charts are important to show the behavior of the tags over time. They may be placed in a HMI associated with the PLCs tags. In the Y axis the tag values are placed, and in the X-axis, the time. This history may be saved to the database.

Control: The setpoints available in the system are controlled by the SCADA system. Limits and presets are changed during the process. Valves, pumps can be also triggered by the SCADA systems.

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