Saturday, September 23, 2023

Industrial Automation using SCADA, HMI & PLC

Vandana R Mesta is an Electronics and Communication Engineer from A. I. T., Chikmagaluru. She has worked as Lecturer at R.N.Shetty Rural Polytechnic, Murdeswar for 5 years

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The SCADA concept was developed as a universal means of remote access to a variety of local control modules, which could be from different manufacturers allowing access through standard automation protocols. They can control large scale processes that can include multiple sites and work over large distances as well as small distance.

A SCADA system mainly consists of a plant computer, supervisory computer, multiple remote terminal units(RTUs)/Programmable logic controllers(PLCs) and communication infrastructure

A typical SCADA System
Fig. 4: A typical SCADA System
  1. Plant Computer: It is a PC or mainframe computer with necessary software responsible for communicating with the field equipment like RTUS, PLCs etc. The SCADA system presents the information to the operator in the form of a mimic through HMIs. i.e. the operator can see a representation of the plant being controlled. For example, consider a pump connected to a pipe. The operator can observe pump is running and how much fluid is pumped through the pipe. He can turn off the pump when required.
  2. Supervisory computers: It refers to the computer and software responsible for communicating with the field connection controllers- PLCs, RTUs and HMI software. These computers gather data on the process and sends control commands to the field connected devices. In smaller SCADA systems, the supervisory computer is a single PC with HMI. Whereas larger SCADA systems has several HMIs hosted on client computers, with multiple servers for data acquisition, distributed software applications and disaster recovery sites.
  3. Multiple Remote Terminal Units(RTUs) or Programmable Logic Controllers(PLCs): Actual control is automatically performed by RTUs and PLCs. They are directly connected to the physical equipment and reads status data from a switch or valve: reads measurements such as pressure, flow, voltage or current. Depending on the program, they process the signal and sends proper signals to control equipment such as closing a switch, motor speed control etc.
  4. Communication Infrastructure: – SCADA systems use combinations of radio and direct serial or modem connections to meet communication requirements. At large sites, Ethernet and IP over SONET is used. This connects supervisory computer system to the RTUs and PLCs and may use industry standard or manufacturer proprietary protocols. They operate automatically on the near real time control of the process. But process continues even during communication network failure. Hence some critical systems will have dual redundant data highways.
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Effective SCADA system can result in significant savings of time and money. Modern SCADA systems allow real-time data from the plant floor to be accessed from anywhere in the world. This allows governments, businesses and individuals to make data driven decisions about how to improve their processes. Control can be centralised by using single system over multiple sites and large distances called Panorama SCADA system. It can monitor and control multiple systems and process simultaneously. These applications range from 50 variables to 1,600,000 I/O operations. One of the suppliers for such system is Electro in partnership with Codra. Without SCADA software, it would be extremely difficult if not impossible to gather sufficient data for consistently well-informed decisions.

Human Machine Interfaces (HMIs) or Man Machine Interfaces (MMIs) is a software application that present information to an operator or user about the state of a process and to accept and implement the operators control instructions. HMIs help in integrating humans into complex technological systems.

A good HMI can provide realistic and natural interactions with external devices. They help in error reduction, increased system and user efficiency, improved reliability and maintainability, increased productivity, increased user acceptance, comfort, less training, less stress etc.

Information and Enterprise level

This is the top level of industrial automation which is more sophisticated. It uses artificial intelligence to manage whole automation system. This level mainly takes care of commercial activities like production planning, customers and market analysis, orders and sales etc. It is less concerned with technical aspects.

Industrial communication networks transfer the information from one level to the other, providing continuous flow of information. It may vary at various levels. For example, RS485, CAN, Device Net etc.

Thus, if we draw a graph to represent these level, we get a pyramid. The top level consists of enterprise level and bottom consists of sensors and actuators. At bottom level, we get detailed information about the process and as we go up information becomes more aggregated or complex.

Automation using SCADA systems can be found in most of the systems. It can be found in modern industries like:  Energy, Food & beverages, Manufacturing, Oil & gas, Power, Recycling, transportation, Water & waste water etc. Also, in day to-day life applications like local supermarket, tracking energy use at home, lift control in a multi-storey building etc.

Thus, there is no doubt that SCADA, HMI & PLCs are playing vital role in today’s industrial automation.




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