Real-time

The term real-time ( real-time english ) characterizes the operation of information technology systems, the specific results reliably within a predetermined time period, for example, in a fixed time frame, can deliver.

Definition

DIN 44300 (DIN = German Institute for Standardization ) defines the term real time as follows:

Due to the hardware and software necessary to ensure that no delays occur which could prevent the fulfillment of this condition. The processing of the data need not be particularly fast here, it must only be guaranteed fast enough for the application done.

The Duden provides for real-time two descriptions, on the one hand as a " given time, which may consume certain processes of an electronic computer in the real world ," as well as " proceeds simultaneously to reality time." For real-time operation in computing the dictionary gives the following meanings of " operation of an electronic computer in which the program or data processing ( almost ) is concurrent with the corresponding processes in the real world ."

Properties

Response time

The term real-time says something about the ability of a system to react to an event within a predetermined time frame. The term says nothing about the speed or processing power of a system. In everyday language, but this is often mistakenly used as, in place of the more appropriate terms with little delay or distortion.

To be referred to as real-time data about in near-time data from weather satellites such as EUMETSAT also a few hours old measurements. Also, in applications such as passenger information systems ( Dynamic Passenger Information ) with further processing of the data in the range of minutes is spoken by real time.

Depending on the application, this reaction time can vary within a wide range:

• For applications such as temperature control or level monitoring reaction times of a few seconds is sufficient are often (realized with microcontrollers cheap, simple programmable logic controller ( PLC) ).
• Automation solutions with a programmable logic controller (PLC ) or a field bus system based production lines typically come out with response times in the millisecond range.
• Real-time applications on the computer such as games or demos require to be perceived as a liquid flow in updating the screen display response times of ≤ 63 ms ( ≥ 14-16 frames per second).
• The response times of computer programs for input by the user with input devices (keyboard, mouse, etc. ) ≤ 10 ms are required to be subjectively perceived as immediately.
• Quick, digital controls, control systems, filtering and monitoring, measurement data online evaluation often require real-time systems that operate in the microsecond range.

Real-time quality

But to describe a control and regulating tasks it is not sufficient to define a real-time over the reaction time. To summarize the requirements for real-time systems more clearly, the reliability is defined in the performance of this reaction time, often more. For this purpose, usually between hard real-time (English hard real-time) and soft real time (English soft real-time) distinguished:

• Hard real-time guarantees that the defined reaction time is not exceeded. This property can be trusted when using a hard real-time system, for example, in recording the timing of the sensor data in a crash test.

• Soft real-time, here's a response time is guaranteed only statistically. While such systems typically operate all incoming submissions sufficiently rapidly, but this is not guaranteed. The response time achieved for example an acceptable average or other statistical criterion. Exceeding the time requirement does not lead to errors or other technical problems.

• Fixed real time is sometimes used to define a sharper requirement than in the hard real-time. For fixed real time no variation is also down at the reaction time allowed ( isochronous ). A practical example of an ADC module should ideally work with a fixed clock rate would be ( in reality limited by the jitter of the clock ).

Applications

Real-time applications are for example:

• Real-time clocks,
• The Global Positioning System (GPS),
• The high -precision real-time positioning service and the Austrian Positioning Service,
• Real -time passenger information systems as Dynamic Passenger Information, for example, in the traffic group region Kiel or tram Potsdam, also integrated into Google Maps,
• The graphic timetable for railways, inland navigation information services in the inland waterways,
• The real-time location in the radio navigation and the Flightradar24 as a cyber - physical system,
• Intelligent information system supporting observation, searching and detection for security of citizens in urban environment ( INDECT ), slightly more complicated than the tried and true test sheet for real- time tracking,
• The real- time decision system ( a real-time decision-making system in the telephone marketing), as well as real-time bidding auction model in advertising,
• The real-time price on the stock exchange,
• Twitter and chat,
• The Collaborative text editing in real time,
• Intelligent Teaching And Learning with Computers ( iTALC ) and other applications in real-time collaboration,
• Live streaming and other streaming media,
• Virtual Reality or the less computationally intensive real-time 3D,
• Applications in digital art, the speed painting or physical modeling of sound generation in computer music and live electronics,
• Real-time computer games such as real-time strategy games
• Applications in weather observation satellites as in Castor,
• In energy and environmental technologies such as the Smart Metering, the intelligent electricity network or environmental information systems such as the remote sensing program Spot vegetation,
• A Manufacturing Execution System in Production Engineering,
• Laser speckle extensometer for deformation measurements,
• The real-time MRI, 4D ultrasound, color -coded Doppler sonography, the neurofeedback in medicine,
• The real-time PCR (English: Real Time Quantitative PCR), a reproduction method for nucleic acids,
• Scientific applications such as photoemission electron microscopy, the Collider Detector at Fermilab, the nuclear quadrupole resonance spectroscopy, or gravitational wave detector in the study of gravitational wave.

Serves the recording with sensors and high-speed cameras in real time, so later the recorded data can be played back at a slower pace ( in slow motion ). On the other hand, can be some physical models by count much faster than real time, such as the star formation in a gas and dust cloud. Here, the fast motion of the ( scientific ) interpretation is attached.