Guide to Connecting PLCs with SCADA Systems

Process industries of all types, such as power, manufacturing, or railway industries, need ways to cut costs, limit downtime, and ensure the safety of the process. To have the ability to monitor problems, gather and process information in real-time, and record events in a log file can solve and limit cost, downtime, and safety issues.

When alarms and failures occur, having the ability to interact with devices, such as sensors, relays, or switches attached to valves, pumps, and motors, will prevent little problems from turning into bigger problems.

Being able to control processes from local or remote stations can make a process more productive and efficient. To incorporate such a system that can do those things for any industry would be invaluable and SCADA systems were designed to do just that.

SCADA systems are connected to PLCs, remote terminal units (RTU), and are able to interface with Human Machine Interface (HMI) software. These are tools that will provide the ability to cut costs, limit downtime, increase safety, and control processes for maximum efficiency.

What is Supervisory Control And Data Acquisition (SCADA)?

The SCADA system is composed of various components such as the supervisory system, the HMI, RTUs, PLCs, communication infrastructure, and SCADA programming.

Supervisory System

The supervisory system can be made up of single or multiple PCs and multiple servers. This is the communication hub between the PLCs, RTUs, HMIs, and sensors and switches.

The purpose is that the PLCs, RTUs, HMIs, and sensors all communicate data, any alarm or fault conditions, to the supervisory system. Also, it provides the ability to react to those conditions by enabling, disabling, or rerouting around any faulty components.

Communication Infrastructure

The communication infrastructure can be composed of the components directly wired together or have the components communicate through a network of radios.

Monolithic SCADA systems can communicate with one another using LAN network lines.

In larger industries, Synchronous Digital Hierarchy (SDH)/ Synchronous Optical Network (SONET), which is the transference of digital data through fiber optics, may be used.

In today's systems, Internet Of Things (IoT) cloud computing is a recent development to allow the components of the SCADA system to communicate.

The SCADA programming is the diagram or map of the monitored infrastructure that will depict important information during a process or event failure or activation keys to perform an action.

What is a Programmable Logic Controller (PLC)

PLCs are attached to sensors, relays, or input devices in order to convert the device information into digital data so the SCADA system can understand what is going on. These not only provide users with information but also allow the user input control over components.

They are easily programmable which is why this device is prevalent in industrial environments.

The different examples of input information into the PLC to the user are on and off states for switches, buttons, and encoders. High and low states for temperature and pressure sensors or liquid-level detectors.

The different examples of human interaction inputs into the PLC can be a button, switch, or sensor activation from a keyboard, touchscreen, remote, or card reader. The physical action output from the PLC when any of these inputs are activated can be starting motors, turning on lights, increasing or decreasing temperature, draining a valve, or turning a pump off.

Connecting a PLC With A SCADA

When connecting a PLC with an existing SCADA system, perhaps with already existing PLCs, there are a series of questions that need to be answered when choosing the one that will work in the existing SCADA application:

If you have any questions about SCADA, contact Mader Electric today to speak with a member of our expert team.