HMI is Human Machine Interface designed for industrial applications. We can think of HMI systems as a “window” of a process. This window can be on special devices such as operator panels or on a computer. An HMI system has connected with both hardware and software components of an industry so that, the HMI can interchange information between the user and the system.
The human-machine interface (HMI) is the collection of screens, graphic displays, and other technologies used by the operator to monitor and interact with the control system
The signals of the process are conducted to the HMI by means of devices with input/output cards in the computer, PLC’s,RTU (remote units) or Drive’s, All these devices must have a communication that the HMI understands.
Functions of an HMI Software:
Monitoring: It is the ability to obtain and display plant data in real time. This data can be displayed as numbers, text or graphics that allow a reading easier to interpret.
Supervision: This function allows, together with the monitoring, the possibility of adjusting the working conditions of the process directly from the computer.
Alarm: It is the ability to recognize exceptional events within the process and report them
Control: It is the ability to apply algorithms that adjust the values of the process and thus maintain these values within certain limits.
Historian: It is the ability to display and store in files, process data at a certain frequency. This storage of data is a powerful tool for the optimization and correction of processes.
Displays should be designed in a hierarchy that provides progressive exposure of detail. Displays designed from a stack of P&ID schematic designs will not have this; they will be “flat” like a computer hard disk with one folder for all the files.
There are four-level display hierarchy:
Level 1 - Operational overview:
Overview graphics are usually not designed for making control interactions. It is an overall indicator as to how the operation is running. It provides clear indication of the current performance of the operation by tracking the Key Performance Indicators.
Level 2- Unit Control:
A process consists of different small units, each unit has its own process system. There is a Level 2 graphic for each separate main unit operation. It is designed to contain all the information and controls necessary to perform almost all the tasks of the operator associated with that section from a single graphics.
Level 3- Unit Detail:
Level 3 graphics provide all of the detail about a single piece of equipment. These are used for detailed diagnosis of problems. They show all of the instruments, interlock status, and other details. A schematic or P&ID type of depiction is often desirable for a Level 3 display.
Level 4- Support and Diagnostic Displays:
Level 4 displays provide the most detail of subsystems, individual sensors, or components. They show the most detailed possible information about the system and subsystems.
Types of HMI:
Developed to measure: They are developed in a graphical programming environment such as VC ++, Visual Basic, Delphi, etc.
HMI canned packages: These are software packages that cover most of the standard functions of SCADA systems.