Telemetry is a technology that allows the remote measurement and reporting of information of interest to the system designer or operator. The word is derived from Greek roots tele = remote, and metron = measure. Systems that need instructions and data sent to them in order to operate require the counterpart of telemetry, telecommand.
Telemetry typically refers to wireless communications (i.e. using a radio frequency system to implement the data link), but can also refer to data transfer over other media, such as a telephone or computer network or via an optical link.
Growing crops has become high-tech business. Most activities related to healthy crops and good yields depend on the timely availability of weather and soil data. Therefore wireless weather stations play a major role in disease prevention and precision irrigation. These stations transmit back to a base station the major parameters needed for good decisions: air temperature and relative humidity, precipitation and leaf wetness data (needed for disease prediction models), solar radiation and wind speed (needed to calculate evapotranspiration), and sometimes also soil moisture, crucial for proper irrigation decisions in order to understand the progress of water into the soil and towards the roots.
Because local micro-climates can vary significantly, such data needs to come from right within the crop. Monitoring stations usually transmit data back by terrestrial radio though occasionally satellite systems are used. Solar power is often employed to make the station independent from local infrastructure.
Telemetry has become indispensable for hydrometry and water management applications, including water quality and stream gauging functions. Major applications include AMR (Automatic Meter Reading), groundwater monitoring, leak detection in distribution pipelines and equipment surveillance. Having data available in almost real time allows quick reactions to occurrences in the field.
Telemetry is an enabling technology for large complex systems such as missiles, RPVs, spacecraft, oil rigs, and chemical plants because it allows automatic monitoring, alerting, and record-keeping necessary for safe, efficient operations. Space agencies such as NASA, ESA, and other agencies use telemetry/telecommand systems to collect data from operating spacecraft and satellites.
Telemetry is vital in the development phase of missiles, satellites, and aircraft because the system might be destroyed after/during the test. Engineers need critical system parameters in order to analyze (and improve) the performance of the system. Without telemetry, these data would often be unavailable.
Telemetry was a vital source of intelligence for the United States and United Kingdom when Soviet missiles were tested. For this purpose, the US operated a listening post in Iran. Eventually, the Soviets discovered this kind of US intelligence gathering and encrypted their telemetry signals of missile tests. Telemetry was a vital source for the Soviets who would operate listening ships in Cardigan Bay to eavesdrop on the UK missile tests carried out there.
Many resources need to be distributed over wide areas. Telemetry is essential in these cases, since it allows the system to channel resources to where it is needed.
Telemetry has been a key factor in modern motor racing. Engineers are able to interpret the vast amount of data collected during a test or race, and use that to properly tune the car for optimum performance. Systems used in some series, namely Formula One, have become advanced to the point where the potential lap time of the car can be calculated and this is what the driver is expected to meet. Some examples of useful measurements on a race car include accelerations (G forces) in three axes, temperature readings, wheel speed, and the displacement of the suspension. In Formula 1, the driver inputs are also recorded so that the team can assess driver performance and, in the case of an accident, the FIA can determine or rule out driver error as a possible cause.
In addition, there exist some series where "two way" telemetry is allowed. Two way telemetry suggests that engineers have the ability to update calibrations on the car in real time, possibly while it is out on the track. In Formula 1, two-way telemetry surfaced in the early nineties from TAG electronics, and consisted of a message display on the dashboard which the team could update. Its development continued until May 2001, at which point it was first allowed on the cars. By 2002 the teams were able to change engine mapping and deactivate particular engine sensors from the pits while the car was on track. For the 2003 season, the FIA banned two-way telemetry from Formula 1, however the technology still exists and could eventually find its way into other forms of racing or road cars.
Telemetry also is used for patients (biotelemetry) who are at risk of abnormal heart activity, generally in a coronary care unit. Such patients are outfitted with measuring, recording and transmitting devices. A data log can be useful in diagnosis of the patient's condition by doctors. An alerting function can alert nurses if the patient is suffering from an acute or dangerous condition.
Telemetry is now being used to study wildlife, and has been particularly useful for monitoring threatened species at the individual level. Animals under study may be fitted with instrumentation ranging from simple tags to cameras, GPS packages and transceivers to provide position and other basic information to scientists and stewards.
At a 2005 workshop in Las Vegas, a seminar noted the introduction of telemetry equipment that would allow vending machines to communicate sales and inventory data to a route truck or to a headquarters. This data could be used for a variety of purposes, such as eliminating the need for the driver to make a first trip to see what items need to be restocked before bringing the inventory inside.
Retailers are also beginning to make use of RFID tags to track inventory and prevent shoplifting. Most of these tags passively respond to RFID readers (e.g. at the cashier), but active RFID tags are available that periodically transmit telemetry to a base station.
Telemetry hardware is useful for tracking persons and property in law enforcement. An ankle collar worn by convicts on probation can warn authorities if a person violates the terms of his or her parole, such as by straying from authorized boundaries or visiting an unauthorized location. Telemetry equipment has also given rise to the concept of bait cars, where law enforcement can rig a car with cameras and tracking equipment and leave it somewhere they expect it to be stolen. When stolen, the telemetry equipment reports the location of the vehicle, and gives law enforcement the ability to deactivate the engine and lock the doors once it is intercepted.
As in other telecommunications fields, international standards exist for telemetry equipment and software. CCSDS and IRIG are such standards.
All links retrieved November 18, 2015.
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