Construction of modern equipment and avionics systems is closely linked to the use of signals in digital form (Fig. 2).
Widespread use of digital technology to build an AC due to many advantages over analog, the main ones are:
- The use of digital computers;
- Improve noise immunity;
- Increased information bandwidth data;
- Reducing the dimensions of avionics and number of wired connections.
The functioning of every digital device inevitably associated with "digital word", which is an analogue the real analog signal at a certain level sampling.
Fig. 2. General principles of building of avionic devices
Under each analog signal supplied to the computer information processing unit should be converted into a binary system. This function performs analog-to-digital converter (ADC). It transforms the signal voltage that changes over time, in a sequence of pulses of the "switched - off". The resulting pulses correspond to a computer logic of its values "yes - no" and the binary system that can express any number regardless of how big it is a combination of ones and zeros. With digital technology zeros and units expressing two states chip, on which is based CPU, memory and other units.
To submit an analog signal into digital form, ADC periodically measures the value of the amplitude in the selected time points, converting the measured value at any point in the binary number.
The value of different variables which are measured by sensors that transform these values to the desired signal. According to the type of output signal can be digital and analog sensors.
In modern digital systems after measuring physical quantity performed the measurement of errors with using mathematical models and certain coefficients (Fig. 3).
Fig. 3. Measurement of physical quantities in avionic devices
After determining the value of some physical quantity in digital form anther added to it either in binary address block or place where you should send this value. Digital values together with the address form "digital word" (Fig. 4). With digital technology, all information is transmitted in the form of "digital words" in a particular format. The structure of the "digital word" depends on the structure of the system and the type of information transmitted.
Structurally devices on board of AC integrated in systems designed for specific tasks. Some systems may unite into larger structures - complexes. Sets of the onboard equipment - is a set of functionally related systems, sensors, calculators.
Fig. 4. Example "digital word"
Due to the limited space, the main avionics systems are placed in a special place for them on AC, and in the cabin only means of information display and interaction and control bodies (Fig. 5) through which a pilot controls the flight systems and AC.
Electronic Indication System (Electronics Flight Instrument System - EFIS) grouped data from various aircraft systems and displays the pilot information necessary at any given flight. After EFIS pilot can get information from any of the systems on the plane to intellectually simple and visual form. In addition, during the flight information EFIS display automatically changes depending on the phase of flight.
Information exchange between the blocks and avionics systems provided through information exchange channels (Digital Data Buses - DDB).
The first standard for digital channel information exchange appeared in 1974. (MIL-STD-1553), which was developed specifically for use in the construction of US military aircraft. At about the same time, aircraft building company Boeing and Airbus to build a civil aviation aircrafts began also apply DDV (ARINC 429) for information exchange between blocks of avionics. Even now ARINC 429 is an integral part of many modern avionic systems.
Using of digital channels of information exchange between blocks of avionics get possible to reduce the number of wires and increase immunity.
Fig. 5. Interaction of avionics
For the organization of complex avionics systems used programs and control processing, forming an operating system that, on the one hand, plays the role of interface interaction between devices and computer system applications, and on the other - is needed to control and computing devices, efficient distribution computing resources between computing processes and organization of exact calculation.
Software plays a major role in the design and development of systems. Modern electronic components that used for creation of blocks require the use of special computer programs for correct operation.