How do you manage a network of remote substations without letting the cost sink you? This was the question that faced power and natural gas companies in the early 1900s. The eventual solution to this problem created the foundation for automation as we know it: SCADA. SCADA stands for Supervisory Control and Data Acquisition. At a high level, SCADA allows for active, central monitoring and control of remote equipment and processes.
Today, you can find SCADA systems in virtually every industry. The efficiency benefits of a SCADA system compared to manually monitoring and adjusting equipment and processes are significant. Consider, for example, a municipal water management system. Pre-SCADA operation would have involved a technician driving from station to station, monitoring water levels and taking control action as needed. Now, thanks to SCADA, a single command center can monitor and control hundreds of miles of shoreline simultaneously.
What goes into a SCADA system?
Fundamentally, SCADA networks gather many datapoints from each remote station and aggregate them into monitored and actionable information. Let’s look at the different pieces of a typical SCADA system.
Instrumentation is the most basic element of a SCADA system. A typical SCADA network consists of instrumentation located with each remote equipment station to monitor/measure its condition or operation. Instrumentation can be as simple as level and flow measurements or as complex as real-time chemical analysis or material composition (think thickness and brightness measurement at multiple points across the width of a sheet of paper as it speeds off a paper machine). Modern manufacturing plants may employ vision systems to check quality. In essence, any parameter of your process or equipment that can be measured can be incorporated into a SCADA system.
RTUs and Telemetry
Instrumentation is connected to a remote terminal unit (RTU) which converts the signals from the equipment into a data stream that is communicated to the central location, where a data concentrator collects the data and feeds it to the operator terminal. Large SCADA systems can have hundreds of RTUs, incorporating thousands of datapoints. The data stream from the RTUs to the central data concentrator is called the telemetry.
Automated data loggers help capture large volumes of telemetry data for review and use without requiring constant operator attention. Solid state technology, improved recording systems, and computerized handling of the data have elevated telemetry into modern monitoring and response systems.
How does the SCADA system communicate?
The communications link itself has undergone massive changes through the years in the technology employed. In the early years, telephone lines were used as the transmission medium, and telephone company step-x-step switching technology was employed for signaling. This amounted to little more than sequences of open-close electrical pulses created by the switches.
Advances in technology allowed improved signaling capabilities, first in half-duplex (one-way-at-a-time signaling), then in full-duplex (simultaneous transmission both directions) mode. Pulse modulation techniques and computerization have made possible today’s systems that can generate and receive the massive amounts of data that feed a modern SCADA system.
Over time, hardwire connections became less practical and more expensive. Radio technology evolved to be the preferred method of communicating telemetry signals. Licensed radio with limited bandwidth and power made its way into the telemetry field. After WWII, spread spectrum technologies became available to the factory floor and SCADA systems, allowing multiple users to operate in the same band.
In the 1980s, the FCC stepped in and divided up frequency bands for different applications, and manufacturers developed a variety of proprietary systems operating in different frequency ranges. Eventually, standards were developed that made spread spectrum and licensed radio good options for implementing wireless communications links within a SCADA network.
But radio also has some disadvantages. Antenna placement and height are often difficult to optimize for signal strength, though radio surveys can minimize this problem by helping to determine the best of both parameters. Another challenge with radio is that antennas high enough to provide proper range and signal strength become lightning targets, causing equipment and system outages and chewing through maintenance budgets.
Radio isn’t the only method of communication within SCADA systems, however. Cellular technology has become common and inexpensive enough to serve as a valid method of communication for SCADA networks. Cellular technology also allows RTUs to be located at ground level, without the need for lightning attracting antennas.
How Does SCADA Help Me?
SCADA is undeniably a fascinating technology, but it’s only valuable if it helps your business. The good news is that, for many businesses, it can! SCADA systems are crucial for monitoring and controlling equipment and processes that aren’t located within your facility. One of the key functions of a SCADA system is alarming, which allows you to select a safe range for a chosen parameter and get notifications if that parameter skews outside your range. As control systems develop and get smarter, many are able to use the data collected by SCADA systems to adjust its setpoints and processes automatically, keeping your systems running more efficiently. Most importantly, SCADA gives you direct access to the data critical to your systems, ensuring that you make informed decisions about your system.
Understand the basics of a SCADA system? Read part two now: SCADA Basics: Cellular vs. Radio?
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