HMI(Human Machine Interface), A link from Man to Machine!

Welcome to another informative blog from about HMI. Today we are going to see all about HMI.

HMI is the short abbreviation of the Human Machine Interface.

In this blog, we are going to see What is HMI? What it is for? Why HMI is important in industrial automation? How it is different from SCADA? Connection of HMI to PLC.

So without wasting much time, let’s dive into this blog.

What is HMI?

HMI is the term used for Human Machine Interface, generally used in the field of industrial automation.

Nowadays widely used for all the applications where remote monitoring is important to control the process parameter.

What is HMI, exactly?

HMI (Human Machine Interface) is a device or software that is used to communicate with the machines or groups of machines in the plant or production area.

HMI directly connect the human with the machine just by translating the huge amount of complex data into accessible information via graphical representation on the monitor.

In this way, the operator has all the necessary tools to control the process.

It is sometimes referred to as Man-Machine Interface (MMI), Operator Interface Terminal (OIT), Local Operator Interface (LOI), or Operator Terminal (OT).


How HMI is used in Industrial Automation?

HMI is mainly used for,

  • To monitor or visualize the process
  • To control the process
  • To visualize trends, alarms, etc.

HMI may come in the form of the built-in screen on machines, computers, tablets, etc. but after all these forms the purpose is the same as an interacting human with machines.



There are lots of information like Pressure, Temperature, Flow, Equipment Running Status, Equipment Fault Status, Alarm, etc. are displayed on the screen of HMI. An operator can operate or monitor the machine status from HMI.

A small plant or industrial site can be controlled or monitored using one centrally located HMI. Many HMIs can be connected in parallel with single PLC. Therefore it will be easy to troubleshoot faults without disturbing the operator.

How does HMI work?

A programmable logic controller(PLC) is used to control the process via a sequential user control logic.

PLC first scans the input stats then process it according to the logic installed in it, after that it activates the outputs like relays, coils, contactor, etc. via the signal from the output card.

But PLC itself is incapable of showing all these data in an easy graphical manner.

A person with access to a personal computer or appropriate software to change the logic in the PLC program can see the stats of inputs and outputs by putting the PLC in online mode.

But this is not the practical way to monitor the inputs and outputs stat and control logic for every other person.


In order to represent all this information, we need certain software that can connect with PLC memory and displaying all the necessary information without giving access to change or modify the logic in the PLC.

HMI is a device that can connect with the PLC on a network and gives all the information of process parameters as well as stats of inputs and outputs without losing the integrity of PLC security.

HMI may be the general-purpose computer screens or maybe the special purpose screen that is mounted on the sheet of a metal frame with the machine.

Most of the industrial HMI comes with the touch capacitive screens that help to operate it in a better way.

Electrical personnel can program the HMI in a way that can be easy to understand the operator about machines and sensor status.


SCADA (Supervisory Control and Data Acquisition) does the same thing as HMI, Although SCADA has some additional functions that differ SCADA from HMI.

HMI can be a part of SCADA, but SCADA can’t be a part of HMI.

HMI usually installed at the field near the equipment, but SCADA generally located at the center of the plant from where an operator can monitor or control the equipment of the whole plant.

⇒ SCADA (Supervisory Control and Data Acquisition) and HMI (Human Machine Interface) are closely related, both are used to represent the plant information’s in a graphical user interface.

⇒ HMI is mainly used to represent the information in front of the user in a graphical manner, SCADA also does the same but it has also gathered the data or have a database to collect the historical information.

⇒ Unlike SCADA, HMI does not record the data or have a database.

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