In large industrial structures, it is impractical or even impossible to control the individual parts of the system because, in most installations, the parts are often located very far from each other.
Thus the need arises to monitor and control them with SCADA and HMI. The main difference between SCADA and HMI is their scope. HMI is actually just a part of the larger SCADA system. Without SCADA, the HMI would be pretty much useless.

“SCADA” stands for “Supervisory Control and Data Acquisition,” which is an integrated system that is used to control and monitor the workings of the individual parts of the plant. The SCADA often control pumps, fans, and other machinery along with their other characteristics. The controlling mechanisms are electronic circuits known as programmable logic circuits or PLCs. The PLC controls the machine as well as polls the sensors for data. The data is then sent to the control room. In the control room, the operator needs to make sense of the data as well as issue commands like turning the machines on or off. 

This is where the HMI, or Human Machine Interface, comes in. The HMI is usually a graphical layout of the entire system with gauges, lights, and controls situated in the corresponding locations of the machines. The gauges show the normal range of operation as well as the abnormal range so that the operator knows if the equipment is within the accepted operating range. The lights may indicate if the machine is working or not, as well as the occurrence of faults. The controls send the instructions to the PLC, which in turn control the machine.

The SCADA is the entirety of the system that controls and monitors the operations of a plant. But in general operation, most of its parts are not really to be dealt with on a regular basis. The majority of the time, only the HMI is visible and interacted with. This makes people think that SCADA and HMI are the same or are different implementations of the same system, when one is just an integral part of the other.

SCADA and HMI are not adding any type of logic into your process or plant, Just

This graphical representation helps us in:

1.     Reduce the process cost of the plant.

2.     It can also support us with safe interaction between operator and machine.

3.     Eliminating the maintenance time and downtime of the machine.

All of this reasons very enough to make SCADA and HMI systems essential parts of the process.

What is HMI system

HMI stands for Human Machine Interface, it might be an application (software) or also a hardware device

unlike the SCADA it is just software, so we can say that it allows the operator or engineers to communicate and exchange data with a machine.

Note the type of data that is supported by an HMI application is totally different from the data of SCADA system, this data can be called the low level of information that is considered by an operator or technician or either an engineer this data could be (state of level sensors – overload indication of motor – alarms …).

What is SCADA system

First of all, and regardless of the theoretical definition of the SCADA system let us discuss the real meaning of SCADA system, as all of us knows SCADA stands for Supervisory Control and Data Acquisition, or we can say it is a software that is installed into a PC (that is responsible
for controlling of the plant), this software supports you with Higher Level of monitoring and control.

So, assume we have an application that supports us with some detailed information about the machine such as ( Motor Amps – Machine state – Rated Temp and Pressure …) this information is not considered as Supervisory information, it may be related to the operator or the maintenance engineer but information like that will not be considered by the manager of the plant, this is could be a low level of monitoring but a supervisor like a manager wants to know somethings like ( amount of production/day – the usage of power – does there is any problem or not …. ) this how the SCADA should be built Just for Higher Level of Monitoring.

Also, the very critical point is the Data Acquisition the manager of the plant or of the production process is not spending all of his time on the SCADA screen, he just opens the history of performance of the plant and checks what is really mean to him.

Major Difference Between SCADA and HMI

Here we are going to say that as the both systems have some differences, they also have a lot of similarities that we are going to talk about:

We can say that Basically, they both serve the same purposes (Graphical Representation)

Both can be developed using the same designing environment

The two systems can be run from a PC

Both two systems can communicate with the controlling device (PLC) using the same protocols