Data telemetry can simplify and speed up the acquisition of critical information from remote locations. Stevens has been a pioneer in telemetry applications for environmental data collection since its development of the first remote environmental monitoring telemetry system, Telemark, in 1939.
Stevens remote telemetry systems take advantage of the latest wireless communication systems to create integrated environmental data collection solutions. The most effective wireless communication technologies for environmental data include cellular, radio and satellite telemetry. We offer a choice of solutions from long-range wireless satellite telemetry to short-range Bluetooth wireless technology, providing a full range of capabilities to our customers for cost-effective data collection from remote locations.
Stevens designs and manufactures certified Geostationary Satellite (GOES) transmitters.
Communications Options for Environmental Monitoring
Wireless communication architectures are relatively simple—they include a modem on each end that emits or receives a defined radio frequency (RF), and an antenna. Since radio waves or signals exhibit very different propagation characteristics depending on their frequency band, engineers design radio systems to take advantage of these characteristics.
Range: 100 m
Bluetooth is a simple two-way wireless (radio) specification for low-cost, low-power, short-range radio links between mobile PCs, smartphones, and electronic instruments. Bluetooth can be used to collect data from remote sites or as a main link to a hub site, with a private radio system used to extend out to another nearby telemetry modem.
While users may still visit a water monitoring location, they may want to communicate via their computer or smartphone without direct cable access to the data collection platform. They may want to install another telemetry modem within 100 meters of the data collection platform. These are good applications for Bluetooth wireless-enabled data loggers. The Stevens Shark RS232/RS485 Serial Port Adapter makes any data logger Bluetooth enabled.
- Quicker, easier site visits. Eliminates the need to open enclosures that house the data logger, in order to establish communications. Can eliminate the need to even leave your vehicle.
- More flexibility to maximize reliability of remote transmissions. Allows the data logger to be posiitoned in a location more sutiable for servicing, while the remote telemetry modem is better positioned for RF performance. Bluetooth enabled radios can interface with other nearby radio, satellite or cell modems for long-range communications in areas that the RF signal is impeded, such as a sewer manhole, valley, or structural interference
- Lower power. Bluetooth enabled transceivers are lower in power consumption than other alternative wireless products used to replace cables and wires connecting portable and/or fixed electronic devices.
- Simplicity of connections. Connections are established dynamically and automatically only when Bluetooth enabled devices enter and leave the Bluetooth enabled radio’s transceiver range.
- No communications cost. Because Bluetooth technology uses the 2.4 GHz frequency band, this is spread spectrum and the communications are free.
- Designed for only short-range communications. Bluetooth is designed for short-range communications—100 m for class 1 radios (like the Shark), 10 m for class 2, and only 1 m for class 3. In addition, while all Bluetooth enabled radios can communicate regardless of the radio’s class range, the Bluetooth communication ranges are typically limited to the highest-class radio being used. Therefore, if a Shark is attached to a data logger, and the Bluetooth enabled computer is a Class 2 radio, you would be limited to the 10-meter communication range.
- Antenna management limitations. Many Bluetooth enabled devices or adapters come with antennas embedded into the circuit board design. Therefore, improving communication range via adjusting or installing a higher gain antenna for such devices is not possible.
- Potential USB adapter conflicts. External USB Bluetooth enabling adapters requires the user to load unique drivers to the computer. Installing multiple wireless communication drivers on one computer may cause communication conflicts with the computer.
Shark RS232/RS485 Bluetooth Serial Adapter
Range: 5 miles
Spread Spectrum radio communications offers organizations seeking to collect environmental monitoring information a robust short-range, low cost solution for transmission of 24-hour data. Government agencies and utilities, among others, rely on spread spectrum to rapidly transmit information on hydrological and meteorological events.
Radio Frequency (RF) organizations, aware of the demand for local radio communications for individual users, have allocated certain frequency bands to be used in a more flexible way. The oldest and most commonly used frequencies are 900 MHz and 2.4 GHz, often called the ISM bands ( Industrial, Scientific and Medical). The main characteristic of these bands is that they are unlicensed, which means that the frequencies are open for public use and require no registration or payment (apart from the radio hardware).
- Low relative cost. Installation and maintenance cost is signifcantly lower compared to a VHF/UHF radio site. Only small batteries and antennas are required as the total power requirements are much less and the frequency is much higher. Additionally, an FCC license is not required.
- Frequency sharing. The ability to share the same frequency band with other users, while incorporating strong data security. Low interference between multiple groups of devices. Sequence codes generated minimize crossover connection properties, enabling individual groups of transceivers to operate side-by-side without interfering with other units.
- High data rates over medium range. A spread spectrum modem can support data rates of up to several megabits per second over ranges reaching up to five miles.
- Reliable, secure and robust. Some spread spectrum radios have the ability to re-strengthen signals for the next radio in line. These “repeater” radios are used to span distances and generally have built-in error correction, encryption and other features, making them a reliable, secure and long-lasting solution for network communication.
- Flexibility. Most modems designed to provide reliable high-speed digital communication between data terminals use spread spectrum technology. These modems can be configured for point-to-point, point-to-multipoint, broadcast mode and as a repeater. The wireless modems support data rates up to 115.2 Kbps.
- Low error rates even with interference. Spread spectrum devices can be deployed to accommodate high data rates concurrently with high link integrity (low error rates), even in the presence of moderate multi-path effects and interfering signals.
- Band pollution in crowded areas. Because these bands are "free" and not sanctioned by FCC license, signals may be heavily polluted by other unlicensed systems. These other competing signals appear as noise to the desired signal and may degrade signal integrity and range.
- Limited communication distance Typically up to 5 miles in good weather with line-of-sight conditions.
- Appliance susceptibility. The 2.4 GHz band can be affected by microwave oven radiation.
VHF / UHF
Range: 30 miles
In every country, the use of the radio spectrum is regulated by certain organizations. The FCC regulates North America and ETSI (European Telecommunications Standards Institute) regulates Europe. These regulators define the allocation of each radio frequency bandwidth: for TV and radio broadcasting, for telecommunication operators, for the military, for data transmissions, etc. The VHF or UHF frequency bands are commonly used. Usually, to transmit over a frequency band, you must obtain a communication license from one of these bodies, register your architecture and buy the right to use the frequency.
Environmental monitoring data are typically transmitted in packets through radio signals using VHF ("Very High Frequency" 30 - 300 MHz, also used for FM radio and television broadcasting) and UHF ("Ultra High Frequency" 300 - 1,000 MHz, also used for television and cellular phones) frequencies. In the United States, there are up to 50 different frequency ranges available in the VHF spectrum and as many as 1600 frequencies in the UHF spectrum. However, many of these frequencies are allocated for specific forms of wireless communication.
A typical VHF or UHF radio (good for up to 30 miles) is an electromagnetic transmission received by special antennas. A license from the FCC must be obtained and coverage is limited to special geographical boundaries. The regulation, licensing, and governing of the radio transmission spectrum varies from country to country. Many countries, for various purposes, provide license-free radio data transmission spectrums. Check with the spectrum management authority in your country for license-free data transmission regulations.
- Cost-Effective. There is no cost for time, no roaming and no long distance charges, i.e. no direct monthly communication fees. A licensing fee is paid to the regulator authority responsible for controlling the frequency bands.
- Reliable, Error-Free Transmission. The data packets sent are error-checked and corrected. If the transmission was incorrect, the same packet is sent again, until confirmation of successful communication.
- Secure. Encryption provides privacy of data, it can be installed on the receiver or at both ends.
- Time-Sensitive. You can be constantly connected and receive the messages right after they are sent or receive them later if you chose to.
- Fast. There is no time spent waiting for a network connection. The network is always on.
- Enhances productivity. Wireless communications offers real-time data to improve decision making. It also provides great employee safety conditions, and allows the existence of virtual offices.
- Low interference (especially compared to spread spectrum radios). Users of these VHF or UHF bands benefit by not having interference from other radios.
- Good communication range. Compared to spread spectrum radios, the allowed output power of the VHF or UHF transmitter is higher, resulting in a a longer transmission range (up to 30 miles).
- Set-up considerations. Deploying radio communications requires a certain amount of study and planning of your needs and limitations. This typically requires an engineering firm to do a propagation study to determine the configuration for the system and if additional repeater sites are required.
- Testing required. The system has to be installed and tested to ensure its efficiency.
- Employee training. Employees must be properly trained in order for the company to effectively benefit from wireless communications.
- Cost of licensing. There are additional costs for licensing in the VHF and UHF bands when used for environmental monitoring.
- Capital expenditures. Antenna towers and repeater sites (if required) could significantly increase the overall cost of a radio telemetry system.
- Line-of-sight considerations. Wireless communications still have a limitation in the amount of miles that separate a transmitter from a receiver. This concept is called "line-of-sight", meaning one antenna must see the other antenna without obstruction. The distance between antennas can be up to 30 miles line-of-sight, and this distance depends on the number of antennas (repeaters) used, the type of antenna and the terrain.
Range: 30 miles from tower
Cellular telemetry is an excellent choice for any monitoring station that is within range of a cellular tower—low capital and service costs, high bandwidth, 2-way communication, and it's fairly ubiquitous.
All analog and digital mobile phones use a network of base stations and antennas to cover a large area. The area a base station covers is called a cell; the spot where the base station and antennas are located is called a cell site. Cell sizes range from sixth tenths of a mile to thirty miles in radius (1 km to 50 km). GSM use much smaller cells, no more than 6 miles (10 km) across. A large carrier may use hundreds of cells.
Each cell site's radio base station uses a computerized 800 or 1900 MHz transceiver with an antenna to provide coverage. Each base station uses carefully chosen frequencies to reduce interference with neighboring cells. Narrowly directed sites cover tunnels, subways and specific roadways. The area served depends on topography, population, and traffic. In some GSM systems, a base station hierarchy exists, with pico cells covering building interiors, microcells covering selected outdoor areas, and macrocells providing more extensive coverage to wider areas.
- Easy installation. Low profile, non directional antenna. Just need to connect the hardware—all configuration is done on-line.
- Low maintenance costs. There's virtually no maintenance, and cellular technology is now mature enough that it is quite reliable.
- Two-way communications. Send new configurations to the remote site while retrieving data from it.
- High data bandwidth. Cellular is suitable for high bandwidth applications such as photos or video.
- Event notification by pager, Internet, other cell phone, etc. Many ways to push alerts to you when conditions are met at the remote site.
- High power consumption. Typical cell modems constantly draw a high current in order to support two-way communictions. Stevens' Cell-Net counters this by staying in an ultra-low power mode, and instead receiving data only on a defined schedule. The result is a 20x improvement in power consumption.
- Requires cell phone coverage area. Many rural areas do not have coverage (yet).
- Ongoing, monthly service fee. May vary depending on local area cell phone service provider.
- Service reliability out of your control. Cell phone service providers may change cell towers or communication protocols, thereby affecting communications to your remote location.
- Connection may be dropped during peak cellular transmission activities. Particularly during storm events or other catastrophes, communication to remote sites is vulnerable. A backup, redundant method of telemetry is recomended for critical data applications.
Geosynchronous Earth Orbit (GEO) Satellites
Range: 1/3 of earth's surface
GEO satellites provide the kind of continuous monitoring necessary for intensive data analysis. By orbiting the equatorial plane of the Earth at a speed matching the Earth's rotation, these satellites can continuously stay above one position on the Earth's surface. Because they stay above a fixed spot on the surface, they provide a constant vigil for the atmospheric "triggers" for severe weather conditions such as tornadoes, flash floods, hail storms, and hurricanes. When these conditions develop these GEO satellites are able to monitor storm development and track their movements.
A GEO satellite's primary purpose is weather imagery to optimize forecasting. In addition to weather imagery, these satellites include instrumentation used in environmental monitoring communications via a relay system. In the United States, this relay system is known as the Geostationary Operational Environmental Satellite (GOES) Data Collection System (DCS). The world network of GEO satellites used with weather imagery and environmental monitoring communications include:
- GOES, USA
- GMS (Geostationary Meteorological Satellites), Japan
- MeteoSat, Europe
- INSAT (Indian National Satellite System), India
- Meteorological Satellite, Russia
- Feng Yun, China
The environmental monitoring market in the United States homeland security applications uses a data collection and relay system for data communications. A Data Collection Platform (DCP) consists of sensor connected to a data logger and the data logger connected to a GEO transmitter (the Stevens SatComm).
The GEO satellite functions as a repeater of the data back to an earth ground station. Web-based software such as Stevens Connect provides easy access to the data collected via GOES.
- Available in remote locations. Since the remote site is communicating with an orbiting satellite, monitoring stations can be located almost anywhere worldwide.
- Low communications cost. Use of GOES is free.
- Low maintenance. Once the transmitter is installed and tested, there's virtually no ongoing maintenance required.
- Emergency event-driven capability. Random window transmissions allow transmission outside of an hourly assigned timeframe.
- Very reliable. GOES transmissions typically have a 98% success rate.
- Hourly transmissions only. Except when taking advantage of random transmissions to send emergency data, GOES transmissions are hourly only.
- Low bandwidth. The amount of data that can be sent in a transmission is limited, so GOES is not suitable for transmitting high-resolution images or video.
- One-way only. GOES does not support sending data TO a remoter station, only receiving data from it. Therefore an additional telemetry method is required in tandem if 2-way capability is required. Thankfully, Stevens SatComm makes it easy to connect a secondary telemetry method.
- Interference detection difficult. There are limited capabilities for troubleshooting interference and other issues (compounded by the fact that a site visit is required without some form of redundant, 2-way telemetry). Stevens SatComm helps in this regard by providing transmitting health status data with each transmission so you can predict problems before they happen. It also provides a VSWR measurement tool to verify the signal quality before you leave the site.
- Available only to governmental agencies. The GOES service is primarily available only to federal, state or local governmental agencies or government sponsored environmental monitoring applications. In addition, all data is available to the government and the public, so data cannot be kept private.
- Capital cost. Although there is no cost for the service, the cost of GOES hardware is more than other telemetry.
- No acknowledgement of successful data transmission. The only way to know if a transmission was succesful is to view the data. If a transmission fails, it cannot be repeated at a later time. Stevens SatComm provides data redundancy, which allows a previous data set to accompany the current data set, increasing the chance of data retrieval even if a transmission is lost.
Low Earth Orbit (LEO) Satellites
Range: everywhere on the planet
Low Earth Orbit (LEO) satellites are in an orbit about 400 to 800 miles above the Earth’s surface—far below geostationary (GEO) satellite orbit. Orbits lower than this are not stable, and will decay rapidly because of atmospheric drag.
A LEO satellite orbits a local horizon in approximately 20 minutes. The orbiting periods range anywhere from 90 minutes to two hours, at approximately 17,000 mph. LEOs are considered to have no delay. A LEO system must use a satellite-to-satellite hand-off to maintain communications and are best for short, narrowband communications. Once one satellite moves out of the area a new one will move in.
We have experience with and integrate with most LEO telecommunications transceivers, including those from Inmarsat, Orbcomm, SkyWave and others. If you're interested in a LEO telemetry system, please contact us.
- Two-way communications. Send new configurations to the remote site while retrieving data from it.
- Available to anyone. Unike GOES, no FCC or other governmental agency requirements are requried
- Available anywhere. There's coverage in even very remote areas—in fact, anywhere on earth.
- Proprietary data. Your data cannot be accessed by anyone else.
- High data reliability. The communications system verifies that data has been transmitted which minimizes risk of missing data.
- Low power consumption. Compared to GEO transmitters, LEO transceivers consume much lower power.
- Monthly service fee and per-byte fee usage can be expensive with frequent transmissions of data.
- Risk of service outage. A power outage at a gateway control center would shut down the communication server, which could delay transmission of data until power is restored (however, no data would be lost). In addition, LEO satellites have a much shorter life span (five to eight years) than GEO satellites, and replacing a satellite could result in a service disruption.