A Starter Guide to SCADA

Introduction to SCADA | What does SCADA Stand for?

What is SCADA and how it works?

SCADA stands for Supervisory Control and Data Acquisition. A SCADA system is a software-based application utilized within industrial manufacturing that controls an array of hardware components. Furthermore, as the acronym suggests, a SCADA system would contain a data component that would provide a historical overview of a system to the user. Such systems are employed within manufacturing environments in order to consolidate controls over multiple production lines, collect actionable data and to drive business decisions leading to process control and improvement.

SCADA system tasks and components

A SCADA system would typically manage an entire manufacturing plant or a large portion of it. A SCADA system is implemented with specific goals in mind. In order to better understand the system implementation process, here are the main tasks of a SCADA:

Control of manufacturing equipment on the plant floor
Control and view of plant floor devices: Programmable Logic Controllers, sensors, valves, variable frequency drives, temperature probes, etc
Display of real-time critical process information
Acquisition, storage, and display of historical data

The architecture of a SCADA system is made possible through a direct connection to the levels below and above within the manufacturing stack. Let’s examine each component and how it is tied into a SCADA system

Instrumentation Layer

The instrumentation layer contains all the plant floor equipment that is responsible for acquiring information and controlling the process directly. This includes photo eyes, temperature probes, pneumatic valves, variable frequency drives, motors, flow meters and more. In other words, every device that either sends or receives a digital or analog signal directly is considered to reside within this layer. This layer would not talk to a SCADA directly. However, a SCADA system receives information from the PLC that will communicate with this layer.

Imagine that the same grinding machine is capable of faulting out. It may stop due to a lack of maintenance (low oil level), unforeseen breakdown (jam at the infeed), or an operator mistake (safety door opened). Each one of these fault states is being displayed by an LED directly on the electrical panel. Since we have this information available, we may choose to add it to an HMI to provide a more granular feedback mechanism to the operator who will eliminate the inherent fault.

PLC and HMI Layer

The devices from the instrumentation layer interface a PLC. A PLC understands the current state of the process by receiving information through inputs and makes decisions and controls the process through the use of outputs. A Human Machine Interface (HMI) would be a local screen that would allow an operator of the process to observe the status of the process and control certain portions. A typical HMI system would display the current status of the system, alarms associated with the asset as well as a control screen used to make adjustments. An HMI would send the information to the PLC and vice versa; it would not interact with the instrumentation directly.

SCADA Layer

The SCADA system would directly communicate to multiple PLCs on the manufacturing floor. Furthermore, many SCADA systems require control systems engineers to create a communication layer that would be instantiated within every PLC in order to pass data accordingly. An important infrastructure within this layer is the network. Although the PLC and HMI layers will require a network for data, the SCADA system would create an additional strain on the plant network due to the volume of data it will consume.

A SCADA system is capable of providing an HMI service in addition to the floor HMIs. The main difference is that the SCADA based HMI solutions would be networked to a server while the ones at the PLC & HMI layer would communicate with the local PLC only.A SCADA system would implement a database to store the data it collects from the plant floor. This database may be dedicated to the system or shared with the layers above. Typically, a new installation during which it is possible to revamp the MES system would centralize the database into a single location backed up with redundancy.

MES - Manufacturing Execution Systems Layer

The MES layer will gather information about the manufacturing process and provide a high-level overview of the raw ingredients to final goods information. In other words, this system would typically track the amount of raw materials entering the plant and the outcome of production activities in terms of final goods produced.

These systems include several sub-systems of various types. OEE, or Overall Equipment Effectiveness, allows the manufacturing facility to track the reliability of equipment on the manufacturing floor. Furthermore, OEE is used as a critical manufacturing metric that will give management information about the production rate of each asset. MES Systems are used in manufacturing, distribution, supply chain operations and more.

ERP - Enterprise Resource Planning Layer

ERP systems extend beyond the manufacturing facility. They facilitate the tracking of assets, raw materials and finished goods to third parties. These may include suppliers, vendors, distribution centers and more. The goal of these systems is to provide the data as well as accountability of the flow of operations. The ERP will create necessary information to manage shipping, receiving, transportation, purchasing and more.

SCADA system components

A SCADA system would typically refer to the underlying software component of the operation. However, as mentioned above, a SCADA system will rely on multiple hardware components within a manufacturing setting. In this section, we’ll explore these components and their role within the system.

Server Infrastructure

SCADA software runs on a server that is located within the facility or on the cloud. An appropriate implementation of this layer is highly critical and will play an impact on how reliable and accurate the data captured by the SCADA system will be. A proper implementation of the server infrastructure would be reliable through dual-redundancy, scalable through virtual machines, and properly networked through adequate networking infrastructure.

Networks

Due to the fact that a lot of data flows to the SCADA system, properly established network infrastructure is required for optimal operation. Furthermore, a vast variety of industrial network protocols makes it difficult to establish this in practice. In terms of best practices, an industrial manufacturing plant should have an established network prior to deploying a SCADA. However, both integrations may happen in parallel. A network that is build to support a growing SCADA system would include switch redundancy, routing tables and VLANs that segment the plant and redundant hardware that would eliminate failure points.

Visualization and HMIs

The SCADA system will collect data from the manufacturing floor and deliver it through dedicated visualization mediums. These may be dedicated Human Machine Interfaces (HMIs) across the floor, computers within control rooms, web interfaces and mobile applications. Regardless of the medium, the presentation of data plays an important role in the system. Therefore, it’s important to be aware of who will be using the SCADA system and how this information will be delivered to these devices. The simplest SCADA implementation will only deliver the data to the plant management.

A SCADA can leverage a distributed topology for the HMI systems deployed in the field. In other words, the data and control systems would be serviced from the server to the floor applications in the form of nodes. This integration requires the components mentioned thus far and provides substantial savings for the manufacturing plant due to the low cost of the terminals that would be required through this distribution.

Programmable Logic Controllers | PLCs

PLCs are the devices with which the SCADA will interact with the most; data will continuously flow between the two. Due to this fact, a robust implementation must be created on both ends. The data that is sent upwards from a PLC should be accurate, buffered and made available despite a disconnect. This requirement is typically met on the PLC side through efficient code that would store the data for a certain period of time before a connection to the SCADA database is established.

Popular SCADA Software

A wide range of SCADA software is available on the market. It’s uncommon for an engineer or technician to be familiar with all of these packages. However, general knowledge and basic familiarity with each system is encouraged for interviews and general control systems knowledge. Each system has its own approach to different components that make it unique and better suited for certain applications.

Rockwell Automation - FactoryTalk View Site Edition and ThinManager

The FTView Studio Site edition from Rockwell Automation is versatile, packed with features and integrates extremely well with other Allen Bradley components. This SCADA system is a step-up from the stand alone HMI Terminals Rockwell provides under the brand of FTView Machine Edition. The main difference between the two being that the Site Edition will run as a server based application and distribute the HMI terminals through light-weight industrial computers commonly called thin clients. Furthermore, Rockwell Automation has acquired a company specializing in distributing these terminals more efficiently which is now under the ThinManager umbrella.

‍More Information | Rockwell Automation - FactoryTalk View Site Edition

Siemens - WinCC RT Professional

Siemens drives a high level of standardization through its software suite called TIA Portal. The WinCC RT Professional is the SCADA package that fully integrates with the suite and provides a high level of efficiency, scalability as well as ease of programming if you’re familiar with their platform.

‍More Information | Siemens - WinCC RT Professional

Schneider Electric [AVEVA] - Wonderware

Wonderware is a SCADA solution adopted by many. The company is offering comprehensive training, support as well as ease of use for their software packages. Primarily due to the ease of use, Wonderware has been the software package of choice for many North American as well as European manufacturing plants.Although Schneider Electric has a line of PLCs and HMIs, the Wonderware platform is standalone and independent from the other business lines. It integrates well with Allen Bradley as well as Siemens components.

More Information | Schneider Electric [AVEVA] - Wonderware

Inductive Automation - Ignition

Inductive Automation is a relatively new player within this domain. However, their modern way of implementing certain features has quickly put them on the map of SCADA systems. Ignition is a platform that features two distinct design patterns that allow developers to create exceptionally well designed screens quickly. Furthermore, the mobile-first web based patterns of Ignition allow it to be used within most browsers, making it highly versatile for most users.A major selling point for Inductive Automation is that the company provides a full trial package based on a 2 hour resettable feature. In other words, the end users are capable of deploying the entire system, test their design and commit to a license once everything is finalized.

The above also makes Ignition the perfect platform to learn SCADA system programming as anyone is able to download the software and create different layouts without the need of a license. Surprisingly, you may run a version of Ignition on a Raspberry Pi.

‍More Information | Inductive Automation - Ignition

What is the main difference between PLC and SCADA?

The main difference between PLC and SCADA is that a PLC refers to hardware, while SCADA refers to software. That being said, the lines are blurred in the current manufacturing environments. In conversation, engineers refer to "platforms" rather than individual components. In other words, a PLC system may include the software that is used to program the device as well. Similarly, a SCADA system will gather information from hardware devices in the field.

So how should you think about the two?

A PLC is the brain of the production floor. It collects raw inputs and controls what happens with the outputs / process. A SCADA system will connect to the PLC and process "non-raw" information and typically control a portion of the process. This means that the PLC is always the first layer of control while a SCADA provides an "overall" control of the system.

What are the 3 main components of SCADA?

We've discussed the main components of a SCADA system above. In this section, we'd like to focus on the 3 main components of SCADA - Field Devices, Field Controllers, and Visualization Infrastructure.

Field Devices include various devices that set inputs and are controlled by outputs. These devices include sensors, motors, relays, actuators, drives, lights, and more. Although SCADA system implementation will vary between industries, manufacturing plants, and businesses, the capabilities will include collecting data on the field devices and controlling outputs. Typically, the SCADA system won't be directly tied to the field devices, but rather interface with PLCs and set the right registers tied to field devices.

Field Controllers are devices that control the process of a manufacturing facility. In most cases, these devices are Programmable Logic Controllers, or PLCs. A PLC is programmed to reliably collect inputs, process the data, and set outputs. A PLC will send information to a SCADA system and retrieve certain information used to control the process.

Example: a PLC is tied to a tank filler that measures the level of the tank and enables a pump accordingly. The PLC will have an input tied to the sensor, and an output tied to the pump. The PLC will send this information to a SCADA system. The SCADA would collect the sensor data and present historical trends on the tank level. It may also allow the user to start or stop the system. Once the user interfaces with the SCADA, the signals are sent back to the PLC and enable the output of the pump.

Lastly, the Virtualization Infrastructure allows a SCADA system to display various information about a process. These devices can be computers, HMIs, web applications, mobile applications, and more. A modern SCADA system will be used to convey information for the users to take action (Ex: alarms) and allow the users to make adjustments to certain parameters (Ex: setpoints).

Learning SCADA System Development

A big step in a control systems engineer’s career development comes at a time where they transition from PLC and HMI development into SCADA systems. Although PLCs may be distributed, they’re still primarily used to control a certain area of a process. Therefore, understanding SCADA systems gives an engineer a high level perspective of an entire manufacturing plant. Furthermore, these systems gather data that goes beyond the technical aspects most engineers are used to. They expose them to higher-management and good business practices that they may not see while programming control systems.

Learning SCADA systems without practicing on a platform is challenging. Therefore, based on the four platforms we’ve covered above, we highly recommend those who don’t have access to a SCADA system at work to practice with Ignition. The trial version paired with exceptional training modules make Ignition an excellent platform to learn how to design modern screens, interface multiple PLC brands and to create databases capable of supporting the largest of manufacturing plants.