Altimeter, or as it is called - altimeter, a flight and navigation instruments for measuring altitude. All altimeters are divided into two main types according to their structure, namely radio and barometric devices.
In the old days it was used as a basic altimeter goniometer, which allowed to determine the height of cosmic bodies, such as a star or a planet.
With this device may determine the relative altitude. This device operates by measuring the pressure in the atmosphere. Everyone knows that with the rise in the height of the atmospheric pressure decreases. It is due to this principle and works altimeter. In fact, it does not measure the height and air pressure, which is determined based on the height.
Structurally, the altimeter is a sealed box, which has a membrane. With the change in pressure diaphragm changes its position. To her between the membrane and the arrow of the device there is a connection. For this reason, the slightest change in the membrane are shown by an arrow on a graduated scale.
These altimeters installed in aircraft with a small maximum altitude. The device is similar to the clock, as it has a circular shape and the two arrows. The main difference is that the board is divided into 10 sectors. One of the arrows, moving one division, said in 100 meters height, and the second, smaller, said elevation changes 1 kilometer.
More recent barometric altimeter to measure the height to allow 20 kilometers above sea level. It should be noted that this construction is unofficially considered the standard in the aircraft industry. There are also altimeters with one hand, a complete revolution in the 360 degrees corresponds to one kilometer high.
It should be noted that sometimes need manual adjustment altimeter given surface pressure on the ground, especially when they are located in mountainous areas. Because of incorrect altimeter setting happened many disasters, the risk increases with zero visibility.
In the CIS countries decided to establish the pressure on the device is the same as the pressure of the airfield, which is carried out planting, it can be considered a point of reference. Western countries as a reference point, a pressure altitude at sea level.
Another point of reference is the height of the so-called line echelon. Echelon - a standard pressure 760 mm Hg. st., which comes on top. It is the height of a conventional line with constant pressure. This imaginary line height is the standard reference for aviation around the world. It should be noted that the landing of all aircraft is prohibited without specifying the atmospheric pressure over the airfield. ICAO requirements stipulate the mandatory presence on board of supervisory altimeter, which in addition to showing the height signals airplane defendant, all this allows air traffic controllers to determine the real altitude vessel.
There are small altimeters, which use commandos and paratroopers jump. This device has a small weight and size, the body is made of impact-resistant material. These systems are installed on parachutes. Currently used and electronic devices that signal the passage of a predetermined height.
Of Radio Altimeter
Altimeter allows you to display the type of Radio Engineering altitude by sending an electron wave in the direction of the earth, after which she bounces and accepted instrument on board the aircraft. It analyzes the return signal is determined by the height of the aircraft above the ground. The main difference from barometric altimeter is that determined by the height of the real, and not relative. Furthermore, this device displays the height with greater accuracy.
Yet in practice, the device is effective at low altitudes as high altitude requires a powerful transmitter signals and associated equipment to filter and eliminate interference.
The system consists of a transmitter and type microwave antenna which is located on the underside of the fuselage of the aircraft. Also there are reflectors and receivers, processing and display system on the instrument panel in the cockpit. Radio engineering altimeters are divided into two types. The first work at heights up to 1,5 kilometer continuously. Second operate from and to 1,5 30 kilometers, but they operate in a pulsed mode. All altimeters have alarm systems low altitude that sound and light are reporting decreases from a predetermined height.
The disadvantage of this device is that the beam from the transmitter is directed straight down. Due to this efficient of Radio Altimeter can be considered only on flat terrain and completely useless in mountainous areas. In addition, when a large roll machine tool displays inflated performance that is not true. Speaking of safety, it should be noted that such devices served the powerful short-wave pulses, which cause damage to the biosphere.
The aircraft altitude may be vymeryat with modern GPS-receivers. This device works by sending signals to multiple satellites that are in constant motion orbit. Mathematical calculations of the device can accurately determine the coordinates of the aircraft and its altitude. The height is measured with respect to earth model type WGS84. It should be noted that the GPS device works with the satellites. So with the help of connection with the two satellites can be set precise coordinates. To determine the altitude necessary connection with three satellites. Work altimeter GPS has much more advantages than barometric and radio equipment, since the definition of height is independent of the parameters of pressure, terrain and roll of the aircraft.
Yet there are some drawbacks to such devices. When used on high-speed fighters very rapid decline does not allow the instrument to display actual performance. In such a situation computing devices must be time to send and receive signals from the satellite, such delays can reach one second. Newer models of GPS-altimeters are able to take into account the rate of decline, making them more accurate.
For low altitudes more accurate and reliable are still barometric and radio altimeters, since they do not affect the signals reflected from the surface and interference from ground electrical systems.
Personal GPS-receivers, which are used in cars or mobile phones may be a deviation from accuracy to 10 meters, enough for effective land navigation. US military and intelligence agencies are using private and more accurate GPS channel called L1, which measures the accuracy of the height of a few centimeters.
The principle of operation of this device is based on the emission of isotopes 137Cs or 60Co, which are sent to the surface and back kicking. Such a device is used at low altitudes of several tens of meters. The main advantage is the stability of rays into which hardly affect interference. Such an altimeter was set on a spaceship "Soyuz" and the product designated as "Cactus". The system was installed on the bottom of the ship and had the appropriate labeling of radiation hazard.
As a result, it should be noted that the height of the flight is very important because its exact definition ensures safety. By virtue of this approach to a certain height must be comprehensive and aircraft should have several different designs altimeters. Only in this way can achieve the accuracy of the calculation. The crew of the aircraft passes deep preparation for work with the devices, which allows the system to analyze all the evidence. Failure of one of the devices during the flight height is equivalent to a flight accident.
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