Telemetry Systems Engineering
Effective Telemetry is Essential
Lots of money is spent on systems to monitor and control remote equipment. SCADA, data acquisition, process control, security, and other systems all require a connection between a host computer and field equipment. Naturally these systems are only as effective as their telemetry. When the telemetry systems are inadequate, the host computer does not report accurate, timely information. When the host does not have good data, it can not make good control decisions. Unfortunately, telemetry systems are often the weak link in these systems.
One of Timberline's clients installed a multi-million dollar SCADA system. Unfortunately, the only telemetry available to them at the time was a radio system shared with other agencies that had conflicting priorities. As a result, field data was updated about once every 20 minutes. Consequently, the system had to be manually operated, and the client did not see the cost savings fully automatic operation promised.
This client hired Timberline to study the problem and design a solution. The replacement telemetry system, based on licensed and unlicensed 900 MHz MAS radios has been installed and is operating flawlessly. Field data is now updated in under 10 seconds and for the first time since the SCADA system was installed, the system can operate unattended.
Telemetry is Complicated - Timberline is Good At It
Many people who design SCADA systems begin with a background in plant process control. When all the remotes are close together and connected with high speed communications, telemetry is not an issue. On the other hand, when the remotes are scattered over a 100 square mile area with hills and trees and canyons, telemetry is much more challenging. In fact, without the proper background in radio frequency propagation, it's nearly impossible.
Our team members have strong academic and practical backgrounds in radio system design. We've been applying this knowledge for our clients' benefit consistently for over a decade.
Sweetwater Authority had a water distribution system with a few of the remote sites monitored over telephone lines. When Timberline designed an expansion of their SCADA system to control the distribution system, we were faced with a challenge. The remote sites were grouped in hydraulic zones along steep canyons inaccessible from the host computer.
Based on a deep understanding of the telemetry options and careful propagation analysis, Timberline developed a telemetry architecture based on spread spectrum radio technology. The host computer communicates with six submasters that each monitor and control remotes in their hydraulic zones. This system uses spread spectrum master and remote radios, one radio repeater, one leased telephone line, and one fiber optic link to communicate with 37 remotes spread across San Diego County.
This system provides tremendously effective radio communications in an area that was fraught with opportunities for marginal coverage and poor performance. Experience, creativity, and careful analysis made this project a success. Contact us to discuss how this talent can be applied to find effective solutions to your most demanding telemetry needs.
Common Sources of Nagging Problems
Unfortunately, many telemetry systems installed in the last two decades have provided their owners with more headaches than they bargained for:
- Systems have been designed with equipment that is now obsolete.
- Systems have been installed in areas subject to interference from other radio systems.
- Systems have been designed with data secondary to voice.
- Systems have some sites that just don't seem to talk.
- Systems that work some days and not others.
Some of these problems can be due to factors that can be seen, others due to unseen influences. Some problems can be solved simply by knowing what to look for:
- Poor facility grounding. Existing and new facilities should meet the grounding requirements set forth in National Electric Code Article 250 and 800. Establishing proper electrical ground on mountain top communications sites is very difficult and usually requires special grounding techniques such as chemical ground rods or self-wetting ground systems.
- Loose or unterminated coax cable. Loose connectors and unterminated coax are non-linear devices that allow transmit and receive frequencies to mix, producing intermodulation interference. Developing an annual maintenance program to inspect radio frequency and intermediate frequency cable connections, integrity of outdoor connector weatherproofing, and integrity of coaxial cable sheaths can help detect and correct these kinds of problems.
- Damaged or misaligned antennas. If your antennas are damaged or misaligned, you may not have adequate receive signal strength to maintain a reliable signal.
- Improper antenna clearances. In many cases, installing an antenna with with line of site clearance to the other end does not guarantee the clearance is adequate. Generally speaking, your antenna should be installed high enough off the ground that a truck parked in front of the antenna won't block the path. The antenna should also be installed at least ten wavelengths above a roof or other obstruction in near field.
Other problems come from factors that you can't see. These factors will impact the performance of your system:
- Interference From Other Systems. Often systems in proximity to one another can interfere. A radio test set with a spectrum analyzer is needed to determine if this is a problem.
- Site Noise. If your transmitter is located on a popular communications site or in an industrial area, you could be subject to noise from transmitters or rotating machinery. This noise can be in the radio frequency band or at the intermediate frequency used by the equipment after down conversion. When the conditions indicate a likelihood of such noise, a good radio test set is necessary to make sure.
- Damaged Coax or Connectors. Occasionally, a piece of coax will be crimped or crushed when it is installed. Connector pins are also subject to damage during fabrication and installation. These conditions result in a range of problems from poor signal-to-noise performance to equipment damage. Testing the VSWR of the coax is a good first step in determining the health of the feed system. More sophisticated tests such as time domain reflectometer traces are excellent for baselining a system or troubleshooting a problem noted in a VSWR test.
- Radio Frequency Blockage and Reflections. An existing path can be analyzed to determine the performance that should be expected. Often, poor performance is a result of a poorly designed path, and no amount of effort on other factors will correct the underlying problem. Path surveys and calculations are necessary to determine if these problems exist. Designing a solution involves the real "magic" with regard to radio communications: the propagation of the signal from transmitter to receiver. Proper path design requires a solid grounding in theory and experience in the "art" of making a path work. It is not possible to answer definitively whether a path is acceptable without an objective for performance. However, once objectives are established, the paths can be designed to meet the objectives. The design must take into consideration frequency of operation, path geometry and terrain, equipment characteristics, average temperature, and a host of other factors.
These are a few of the most common problem areas for telemetry system. An experienced eye can detect many of these issues and recommend the solutions that will provide the most benefit for the least effort.
All too often the performance of a system gets so bad, the owner just stops using it. In Santa Fe, New Mexico, telemetry for the major water production line for the City stopped working every time it rained or snowed on the mountain above Santa Fe. The problem was so bad for so long, that the water company stopped using the SCADA system. The water company assumed that weather was the problem and they could never use radio.
Timberline studied the problem and determined that a number of design, installation, and maintenance issues were at play. Any of the issues in isolation would not have made the system unusable. However, there were so many different elements to the problem, solving even several of them in isolation would not have fixed the system. Timberline recommended upgrading the radios to digital technology, reconfiguring the system to provide proper clearances, and insuring proper installation techniques. Due to this effort, Santa Fe now has a SCADA system that operates better than they believed possible.
Top Three Things You Can Do to Ensure Success
Of course, if you are planning to upgrade an existing telemetry system or you need an entirely new system, you'd like to avoid the kinds of problems discussed above. There are things you can do at the beginning of the project to ensure the project is successful and you have years of troublefree operation from your system. While these tips seem like fundamental common sense, they are probably the most overlooked aspects of telemetry projects!
- Establish Performance Requirements. You must understand at the outset the performance you require from your system. Without these requirements, you cannot know if your job was successful. These requirements include criteria for data throughput, acceptable number of seconds per year the system can be unavailable due to all causes, environmental criteria such as peak wind load and temperature extremes the system must be designed to accommodate, and survivability during any defined natural disaster, such as earthquake.
- Convey the Requirements to a Qualified Contractor. Once the requirements are understood, a system must be designed to meet the requirements. The design includes proper analysis and calculations and the preparation of equipment specification and installation instructions for a contractor. The specifications and drawings must indicate the equipment requirements, installation methods and standards, testing requirements, requirements for system turn-up, and requirements for documentation and training. The testing requirements must be detailed enough to show that the system meets the established performance requirements. These documents must be clear, biddable, and constructable.
- Provide Knowledgeable Observation During Construction. Having a well designed system with detailed, biddable, constructable specifications will produce the desired result only if the contractor understands and follows the instructions. Knowledgeable observation during construction is crucial to ensuring the successful outcome of the project.
Full Service Telemetry Expertise
Whether you'd like an opinion about concerns about your existing system, you are ready for system upgrades, or you need an entirely new system, Timberline has the expertise to make your project a success. Timberline can help you with all phases of your telemetry project. Click here to see the range of services we offer.
Timberline is experienced in the following telemetry applications:
- UHF/VHF radio.
- 900 MHz multiple address system radio.
- 900 MHz spread spectrum multiple address radio.
- Cellular telemetry.
- Trunked radio.
- VSAT / GOES satellite telemetry.
- Analog and digital microwave radio.
- Wireless Ethernet networks.
- Single mode and multimode fiber optics.
- Telephone (dial up, leased line, ISDN, ADN, DSL, frame relay).
Designing a telemetry system often requires expertise in many of the related specialties that Timberline offers:
- Radio frequency interference analysis.
- Radiation exposure analysis.
- Site development plans.
- FCC licensing.
- Antenna supporting structures.
- Anomalous propagation analysis.
- Performance troubleshooting.
- Network security.
Please contact us to discuss your unique telemetry application with one of our design professionals. Let us show you how we can help in planning and designing a telemetry system for your application.