February 2013, Vol. 240 No. 2
Features
Seven Questions To Ask Before Building Satellite SCADA Network
Traditional satellite communications have had a stigma of being expensive and requiring large, power-hungry terminals that are complex to integrate with your applications.
For this reason, satellite services for Supervisory Control and Data Acquisition (SCADA) applications, low data rate (LDR) solutions and other remote unmanned machine to machine (M2M) monitoring management services have, until recently, only been thought as a last resort option used only where landline or cellular networks do not reach.
Today’s modern satellite communication services offer a range of new options specifically designed for SCADA and remote monitoring applications. These options bridge the gap, provide reliable, cost- effective satellite services using small, low power-consuming terminals that are easy to install. Global remote management applications such as those that monitor oil and gas pipelines, Smart Grids, track vehicles and vessels are leaning toward satellite communications over traditional cellular and terrestrial solutions as satellite not only increases reliability but also reduces the total cost of ownership.
This article describes why satellite communications is a cost-effective and powerful solution. By exploring seven key questions, you will understand how satellite SCADA solutions meet your key requirements and how these services support modern SCADA applications.
For the remainder of this article, SCADA will refer to any remote monitoring solution – whether it is for SCADA, LDR or M2M – covering situations such as monitoring the flow of natural gas through a pipeline, monitoring the pressure of an oil well or sending weather data from a remote weather station.
Evolution Of Satellite Communications – Reducing Cost Of Ownership (subhed)
Within the SCADA and other industries, there are many misconceptions of what today’s modern satellite communications actually are, such as:
- Expensive to operate and maintain
- Complex to install
- Large and requiring significant space to install
- Requiring significant amounts of power to operate
- Unreliable in harsh weather
Today, there are new satellite terminals designed specifically for SCADA applications. These solutions operate with extremely low power consumption, are easy to support, easy to maintain and can be installed without any specialized skills The total cost of ownership is much lower than before and certainly lower than the misconceptions would have you think. New low-cost airtime usage bundles are ideal for the majority of SCADA applications.
As an example, in Canada, pipeline monitoring of oil flow from the oil sands of Alberta is necessary to maintain delivery of oil to distribution centers. This traditional satellite solution normally requires antennas of at least 1.2m diameter; sometimes with anti-icing technology in the colder areas; an enclosure for modem/network devices; and, trained satellite technicians to install/design the solution. Many times the installation costs exceed the equipment costs.
The new Hughes 9502 M2M is a prime example of a terminal specifically designed for SCADA. Its small, simple two-piece design uses only an outdoor antenna and an indoor modem connected by an RF cable. With a simple pole mount design, setting up the terminal is as simple as pointing it in the approximate direction of the satellite – the terminal’s browser based user interface will let you know when it has acquired the strongest satellite signal. Its stand-by operating power is less than 1W. The terminal also features a “Watchdog Timer” which automatically reestablishes a satellite connection in the event it is lost. It can also be remotely managed using SMS commands.
The evolution of modern satellite services is bridging the gap, providing more attractive alternatives than cellular or terrestrial solutions.
SCADA Networks – Remote Management At Its Best
SCADA systems are networks collecting data from equipment sensors that transmit and receive data with a distant control center. Each sensor monitors operating parameters, such as temperature, pressure or video (for security). Terminals collate and transmit data from all sensors. Sensors also receive data from control stations to optimize their control parameters. The size and scale of a SCADA network varies depending on the scope of the particular operation – some have only a few sensors while others are large and globally connected.
Seven Questions To Ask Before Building A SCADA Network
Building a SCADA network can be complex, with many requirements and variables to consider, all of which will affect total cost of ownership and network performance. Many of the variables are very specific to your situation. However, there are seven fundamental requirements that drive the key questions you should ask yourself in order to design the SCADA network that is best for you:
1: How much data, in kbytes or Mbytes per month, will each remote terminal transmit and receive?
You need to base your SCADA network on the amount of data that you expect to transmit on a monthly basis. How many kbytes or Mbytes will each of your terminals transmit and receive on a monthly basis? As mentioned earlier, terminals collate data from sensors in the network and push it to a control station. Conversely, these terminals also receive data from the control station to optimize their control parameters. Knowing what information you are sharing back and forth can help determine how much data each terminal sends and receives per poll, or transmission.
In most cases, SCADA systems poll remote terminals at consistent time intervals, so you can easily calculate monthly terminal. If you poll your remote terminal every 15 minutes, there are 96 polls per day. At 10 kbytes per transmission, that would be 960 kbytes per month, or 28.8 Mbytes per month. Be careful if terminals poll based on events (such as alarm driven polling) you will need to conduct more statistical analysis to determine the average data use per terminal.
Optimized based on cost, power consumption and size, modern SCADA satellite services are now available that cover the full spectrum of monthly data use requirements – from the very low to the very high (see below).
2: How frequently will I poll information from my remote terminal?
SCADA applications generally poll for information at regular intervals such as once a day, once an hour, every five minutes or even every 30 seconds. The more frequently you poll, the more data you send across your network and the more power you will need to fuel the remote terminals.
Situations where conditions change every few seconds, or possibly even faster, need near real-time updates – as we see in the oil and gas sector. Typically, the data packets sent for SCADA are very small, so speed of transfer is not an issue. But the volume of data moving across your SCADA network will quickly add up at month end. Therefore, for frequent polling monthly, flat-rate price plans are typically more economical versus pay-per-MB plans.
Modern satellite SCADA terminals generally stay in a low power state (idle mode) when they are not transmitting data. Every time a terminal changes state from idle to transmit, it uses additional power. So, increased frequency of communication can have a significant impact on your final power budget.
3: What is the power source for each terminal?
One important requirement to consider is availability of onsite power. Some SCADA solutions rely on mains power or generators while others can comfortably run on batteries and solar power. As a rule, the more power you require the more expensive and complex your remote power solution.
As SCADA is usually a very remote application – a pipeline may travel through very remote territory to bring oil or natural gas to a distribution point – you cannot rely on access to reliable mains power. Yet, access to a power supply is essential, not only to operate the communication terminal but all remote sensors and control systems as well. You may need to consider asking your provider if solar power, batteries or other power options are available.
Based on Shannon Heartly’s Information Theorem(1), there is minimum amount power required to send information. The more information you wish to send, the more power you require. Once you have answered questions 1 (how much data) and 2 (how frequently do I send/receive data) you can then determine how much power you need. Choose your satellite provider carefully as many do not offer low power satellite solutions.
You will also want to ensure that your system optimizes its power consumption so you are not wasting money or energy, particularly in a remote setting.
4: In what kind of environment will each terminal operate?
SCADA solutions generally operate in very harsh environments. You need to understand the environment in which your SCADA network will operate in order to choose the best-fit terminal and service. Weather not only affects the remote terminal, it affects the availability of the communication service. Heavy rain, snow and even dust can degrade communication services. Choose your service based on its reliability in the typical weather you expect for your SCADA sites.
Do your homework. Learn what frequency band a satellite operator uses and ask for their availability statistics. Some frequency’s fair better in harsh weather, particularly heavy rain, and some networks are more robust. Ask how your terminal will stand up in extremely hot or cold temperatures, dry dusty conditions or very wet tropical conditions. New SCADA satellite terminals are engineered for harsh weather. You may also consider custom or included enclosures as added protection.
5: How secure must my data be?
Defining your SCADA security requirements can be an extremely difficult task. However, everyone implementing SCADA solutions acknowledges its importance. Once compromised, trying to fix your security vulnerabilities after the fact is an expensive task. Simply put, you must implement security to your SCADA network upfront to avoid malicious attacks.
Look for a SCADA network that provides the level of security you need. Your security protocol should call for your system to bypass the public Iinternet; depending on your budget and security concerns there are many options available. Consider options such as leased lines, MPLS circuits3, encrypted virtual private networks4 or VSAT backhaul. Obviously, the more complex the option the more expensive. This is where your own cost-benefit analysis of the cost of security versus your peace of mind factors.
6: How much network downtime can I tolerate?
All communications services, no matter what service you choose, suffer downtime (outages), be it weather or hardware related. For your SCADA network, downtime may mean lost production and revenue, particularly for those who choose to poll for data in real-time. To be realistic, determine how many hours of acceptable downtime you can afford in one year and convert this to a percentage. For example, 100 hours in one year equates to approximately 98.9%.
Most satellite providers design their services around achieving specified satellite network availability. Some SCADA solutions use cellular communications to transmit data. Be careful as the majority of cellular providers will not guarantee service availability.
Another aspect to consider is the level of support and SCADA expertise from your provider. Today, most satellite operators monitor their network 24/7, and provide 24/7 customer support. Look for operators focused on SCADA solutions and be aware that many cellular companies may fall short on being able to support your network.
7: Does the terminal use a Serial or IP protocols to communicate with the remote sensor?
IP communication is considered the industry standard for data communications, surpassing serial-based protocols. New remote sensors and remote terminal units use IP protocols though a large number of remote sensors still communicate using serial-based protocols such as RS-232 and RS-485.
A problem arises when your remote serial based sensor communicates over an IP link. This is common with SCADA networks, so you should look for an IP-to-serial converter, or terminal server, to translate the protocols. However, this does mean another device that draws power and takes up space. Some satellite SCADA solutions accommodate combinations of IP and serial-based protocols.
Choosing Your Satellite SCADA Network
Once you have answered these questions, you have identified your basic SCADA requirement and can narrow your search for the terminals, network and security options that are right for you. Consider today’s range of satellite SCADA services that meet the requirements of even the most demanding SCADA networks, with a lower total cost of ownership than traditional satellite services. And, finally, choose your SCADA provider based on their experience, focus on SCADA services, and network availability.
Conclusion
Today’s modern satellite SCADA services offer a range of options suitable for virtually any SCADA network and should be considered even if cellular or terrestrial services are available. Providing cost- effective services using small, low power-consuming terminals that are easy to install, satellite based SCADA networks have increased reliability and lower total cost of ownership versus cellular or terrestrial. More global remote management applications, including monitoring oil and gas pipelines and Smart Grids and track assets are relying on satellite communications. Based on the seven key questions explored in this article, satellite based solutions meet the requirements for even the most complex SCADA network.
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