[vc_column_text css=”.vc_custom_1648565144628{margin-bottom: -130px !important;}”]So, you need a SCADA system. Or perhaps you have an unreliable system that’s in need of an upgrade. Maybe you’re just curious about what’s out there. Whatever brings you to this post, if you’re thinking through a SCADA system, few decisions you make will be more important than the telemetry communication technology you choose. After all, if you’re gathering monitoring data at remote sites but can’t access it centrally, you’re flying blind and wasting money. For the purposes of this post, we’re going to assume you know the basic components of a SCADA system. (Need a refresher? Read part one of our SCADA Basics series: What Are SCADA and Telemetry?)
What are my options? How do I choose?
When an RTU gathers monitoring data, it has to submit that data back to the central SCADA data aggregation point. However, there are multiple telemetry communication options to choose from. How do you decide? We’ll be upfront and acknowledge that there is no one-size-fits-all solution to this question. Many variables affect which system is best, but some basic overview info can help you narrow down your options. Let’s look at the three most common choices and summarize with pros and cons of each.
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1. Spread Spectrum (Unlicensed) Radio
What is it?
Spread Spectrum (or unlicensed) radio is likely the most common telemetry method. A Spread Spectrum system uses radio waves to transport your data between RTU and data aggregator. It uses an FCC-defined but unregulated band of radio waves in the 900MHz range (at a maximum of 1 Watt) to move your data. Developed in World War II as a way to prevent Axis enemies from intercepting radio signals, these radios transmit data in a specific frequency pattern that the receiver is listening for. For example, you might set your radio send the first bit of info on 921Mhz, the second on 925MHz, the third on 929MHz, and the fourth on 936MHz. Your receiver is programmed to move in concert with this pattern, ensuring that you receive the full picture of data while avoiding being on the same channel for long.
What are the benefits?
Spread Spectrum has its advantages. For starters, it’s unregulated by the FCC, meaning that you can purchase, install, activate, and retune a system as needed, without filing for permits. The radio equipment itself is relatively cheap, and there is no subscription required. After initial equipment costs, there are no repeating costs other than maintenance, and you own your own equipment and broadcasting rights. Radio is also considered a very secure data transmission method, thanks to over the air encryption, the extensive knowledge and equipment required to intercept, and the distance limitations (a malicious actor is required to be within the limited range of the radio waves to intercept).
What are the limitations?
Though common, Spread Spectrum has drawbacks. It requires direct line of sight between transmitter and receiver, which means that the signal can be dramatically affected by physical interference like trees, foliage, buildings, and mountains. Thanks to the line of sight requirement, the antenna towers sometimes have to be very tall to transmit over obstacles. In the most ideal weather and antenna conditions, Spread Spectrum can reach up to 15 miles. However, with generally average conditions and sufficient line of sight, a more reasonable expectation is 1-2 miles. Another major drawback to radio in general is the threat of lightning strikes. Though many radio antennas have good lightning protection, you can’t prevent everything, and lightning strikes can mean substantial downtime and cost to replace.
When might it be used?
Spread Spectrum radio is often used in shorter range applications where infrastructure already exists to transmit and receive signals (think water towers, utility poles, or even office/plant buildings). It can also be useful in remote areas where cell coverage is spotty or there are few competing signals. Though most SCADA systems use little data overall, Spread Spectrum’s 900MHz range typically allows for quicker transfer in ideal conditions than licensed or cell.
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2. Licensed Radio
What is it?
As you may have guessed, Licensed radio is pretty similar to Spread Spectrum radio, with a couple key differences. First, Licensed radio applications are regulated by the FCC, meaning that you submit a permit and they tell you where on the radio spectrum to broadcast. This typically falls below 500MHz, though certain situations can allow for use of a 900MHz band. Second, the power level of Licensed radio is increased to up to 10W.
What are the benefits?
Many of the advantages of Spread Spectrum apply to Licensed radio as well. You own your own equipment, there are no ongoing subscription fees, and security is strong. Alongside these, thanks to increased broadcasting power, Licensed doesn’t have the same strict line of sight requirements as Spread Spectrum because it can better avoid obstacles. It also has much further range at ideal conditions, operating at up to 35 miles. Finally, the FCC regulation typically ensures that interference is kept to a minimum.
What are the limitations?
Though it doesn’t have the same direct line of sign requirements, Licensed radio still requires general line of sight, meaning that taller antenna towers can still be needed to ensure transmission success. Additionally, at the higher end of Licensed radio’s range, the curvature of the earth comes into play, necessitating higher still towers. Licensed radio also typically moves data slower than Spread Spectrum, though not necessarily enough to make operational differences in most cases. Also, the other side of the FCC regulation coin is that you’re not free to retune your radios if needed; you’re locked into a certain range unless you get permission to switch. Licensed radio equipment is also at the same lightning peril as Spread Spectrum.
When might it be used?
Licensed has many of the same use cases as Spread Spectrum. Startup cost and time are higher for Licensed, but despite that, Licensed is often used in situations where distance or interference make Spread Spectrum unreliable.
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3. Cellular
What is it?
Though different than radio, you’re probably pretty familiar with cellular technology. Fundamentally, whereas radio is required to transmit directly from point A to point B, cellular technology uses a grid of towers, forwarding point A’s data from “cell” to “cell” to reach point B. This cuts out the most critical of radio’s flaws: physical interference in the line of sight transmission. When thinking about cellular, feel free to use your experience with your cell phone; it’s the same technology (maybe even the same towers!).
What are the benefits?
The largest benefit of cellular transmission is the lack of interference. Outside of massive disasters that overload or take down towers, cell companies have a vested interested and massive resources committed to keeping their networks active at all times, which benefits your SCADA system. Similarly, as cell networks have expanded across the nation, distance isn’t an issue with cell; if you have network coverage, you’ll get your data. Cell also carries an infrastructural advantage, both in size and cost. No need for large towers and lightning-prone antennas; you just need a three-inch antenna and you’re set. This reduces your potential maintenance and replacement liability substantially. Also, your cell equipment is likely cheaper upfront, reducing the overall initial investment in your system.
What are the limitations?
Obviously, the primary limitation of cell coverage is just that: coverage. If you don’t have cell signal, you won’t get your data. Another downside of cellular is that once you pay for equipment up front, you’re still required to pay for subscription fees for the life of your system. SCADA systems rarely use much data, so these costs aren’t often super high, and they are often offset by minimized maintenance costs over radio, but it’s worth noting that your cell system will never be cost-free to operate day to day. The last major disadvantage of cell is the security aspect. While radio has inherent security as noted above, standard cell data transmissions are online, meaning that a malicious actor at a remote distance can potentially attack your system. There are private networks available through cell coverage providers that essentially eliminate this risk, but they might cost extra, depending on the application.
When might it be used?
Cellular is probably the most versatile of the three options. Unless you lack cell coverage, cellular can be used in nearly any situation, with less investment and simpler startup than either radio solution.
Other options include DSL/cable, satellite, and fiber option, but these are best in very few situations. As you’ve seen, there are a number of factors that affect which telemetry communication technology you might choose, but these are the three primary solutions, because they cover nearly any application. Your best bet is to talk to a SCADA expert who can analyze your specific situation and deliver the best system.