SCADA and Automation SCADA: Decoding the Acronym Supervisory Control and Data Acquisition Systems Play a Vital Role in Our Water Infrastructure By Tyler Dupp, CET, CWNA, Eramosa Engineering and Graham Nasby, P.Eng, PMP, CAP, City of Guelph Water Services SCADA – Supervisory Control and Data Acquisition – it is something that everyone in the water sector deals with at one level, but what are these systems and how do they work? To many, SCADA is just the computer terminals that they sit at every day, which display process screens that represent what is going on in the real world just beyond the control room. To others, it is a necessary part of any design or construction contract, which is tricky to implement and always seems to require a group of specialized ‘computer nerds’ to get it up and running. Still for others, they know SCADA is there but what it does and how it works remains a mystery. The common thread is that whenever SCADA stops working, it becomes immediately noticeable. Without SCADA systems, it would not be possible for us to run our plants and facilities as smoothly and efficiently as we do today. This issue of INFLUENTS is all about automation, so it is only appropriate to start off with the big question of process automation: ‘What really is a SCADA system?’ To answer this, let’s start with the wording of the question itself, specifically the word ‘system.’ In any installation, the SCADA system is comprised of a number of discrete parts that all have to work together to make a complete system. Put another way, the SCADA system is not one particular piece of software or equipment; rather it is many separate sub-systems that are tied together. It’s the reason why those who work on SCADA are often referred to as ‘system integrators.’ It is their job to look after putting together and configuring the components that make up a modern SCADA system, and ensuring that they all work together to provide a fully integrated and smoothly operating system. Another way to look at SCADA systems is to think of them as a jigsaw 22 INFLUENTS Winter 2015 Figure 1 – Block Diagram of a SCADA System puzzle. While individual pieces may be odd looking and hard to fit together, once they are assembled they form a complete picture. It is a puzzle of numerous parts working in harmony to accomplish what its acronym describes: Supervisory Control and Data Acquisition. The SCADA system allows for the seamless automatic control and monitoring of plant equipment while acquiring data to be presented to a supervisory agent (e.g., an operator). Structure of SCADA Systems SCADA systems can be thought of as a hierarchy of equipment, wiring, panels, and computers. A schematic diagram can be found in Figure 1. At the bottom are the field devices, which consist of instruments (sensors, transmitters and analyzers) and output devices (pumps, valves, blowers). The next layer is the field wiring that connects the field devices to the SCADA control panels, which exist in the layer above. The SCADA control panels include the SCADA system controllers (e.g., programmable logic controllers (PLCs), remote terminal units (RTUs), and programmable automation controllers (PACs) as well as the input/ output (I/O) terminals that the field wiring connects to. For some field devices, particularly control devices, an intermediate layer may exist between the field devices and the SCADA control panels. This is the case for motors (pumps, blowers, fans) which typically may use motor starter panels or motor control centers (MCCs). For these types of equipment, Click HERE to return to Table of contents