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HMI series LRH… – 01 What a HMI is

The acronym HMI stands for Human Machine Interface and it refers to those operational panels (OP) that allow the final user to communicate with a machine or a production plant. This works through the collection of data coming from instruments that are locally installed (PLC, multimeters, control units etc…), the elaboration and therefore the representation on the touch screen display of the collected information through an user-friendly interface.

The HMI of the series LRH, available in three different formats 4.3”, 7” and 10.1”, are equipped with touch screen display  resistive at 64k colours and LED-backlit. The Ethernet port, USB and serial (configurable as RS232-RS485-RS422)  allow to establish an interface with any device that uses the protocol Modbus RTU, Modbus TCP and OPC UA.

Please, see here all the technical information.

Supported communication protocols

The HMI series LRH support the following protocols of communication:

  • Modbus RTU, in the Master and Slave version
  • Modbus TCP, in the Client and Server version
  • OPC UA, in the Client and Server version.

The protocol Modbus, thanks to its simple use, is one of the most common serial communication protocol in the industrial field for the acquisition of the information from devices which are locally installed. It is available either in the RTU version (usually used on the serial port) and in the TCP version (that runs on the Ethernet port).

The protocol OPC UA is very common in the automation field. Its main advantage is that the HMI can read information coming from locally installed devices with a standard language that does not depend on the devices’ supplier and on the language protocol that they use to communicate.

Programming Software and scenarios ready to use

The software LRHSW allows a user-friendly and an advanced programming of the HMI, with the possibility to collect data, to present trends, to visualize interactive and customized graphics, to set alarms, to memorize recipes and many other functions.  Scenarios for applications as remote control of a micro PLC, monitoring of a pumping station and a photovoltaic plant are available.

Download the software LRHSW for programming the HMI in free trial version here.

Communication between PLC and HMI

PLCs are frequently used in the industrial plant for the processing of the data coming from the plant itself (temperature measures, alarm signals, etc…). Therefore, the almost all the HMI must communicate with them. The connection between HMI and PLC, usually of a serial type, is generally point-to-point. That means that a HMI usually corresponds only a PLC. It is however possible to set on communication an operator panel with more PLCs. The whole system that run a plant is usually realized through the program loaded inside the PLC, leaving the operator panel only the function to visualize and, if necessary, to modify the information.


Laboratori tecnologici ed esercitazioni (Carlo Ferrari, Ed. San Marco)