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5.3 Data conversion
 

5.3 Data conversion

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  • Αναλογικά σήματα που υπάρχουν στη φύση:Το φως του ήλιου κατά τη διάρκεια της ημέρας Η θερμοκρασία κατά τη διάρκεια της ημέρας Ο ήχος
  • Συσκευές με αναλογικά κυκλώματα:Η κουζίνα (εναλλασσόμενο ρεύμα – θερμοκρασία του ηλεκτρικού ματιού)Ηλεκτρικό καλοριφέρΠίνακας της ΔΕΗΗχεία
  • Ευελιξία: Τοίδιο κύκλωμα με διαφορετικό software κάνει άλλα πράγματα Κατανάλωση ενέργειας + μεγαλύτερη ταχύτητα + μέγεθος  εύκολη σχεδίαση (βελτιώνονται οι τεχνολογίες κατασκευής και τα σχεδιάζουν σε μικρότερη κλίμακα, έτσι ώστε να είναι πιο γρήγορα και να καταναλώνουν μικρότερη ενέργεια) Αξιοπιστία: θόρυβος Αποθήκευση: Στο αναλογικό ο θόρυβος θα καταστρέψει τα δεδομένα.

5.3 Data conversion 5.3 Data conversion Presentation Transcript

  • Module 5: Digital Techniques and Electronic Instrument Systems 5.3 Data Conversion
  • Analog and digital signals Analog signal: can take all possible values. -2 -1 0 1 2 0 5 10 Digital Signal: can take specific values (discrete values). 0 1 2 3 4 0 5 10 0 2 4 6 0 2 4 6 8 10 0 2 4 6 0 5 10 15 2
  • Analog and digital circuits 3  Analog circuits: Input and output signals are analog.  Digital circuits: Input and output signals are digital. -2 -1 0 1 2 0 5 10 -1 0 1 2 0 5 10 0 2 4 6 0 5 10 15 0 2 4 6 0 5 10 15
  • Digital circuits advantages 4  High reliability  Easy design  High flexibility  Easy storage
  • Digital signals on the Aircraft  Digital signals on the aircraft:  Discrete values, usually binary values: on / off, high / low.  Examples:  Is the aircraft on the ground or on the earth?  The Air Data Computer calculates the airspeed, the altitude, the temperature etc. from data sensor inputs. These inputs are send to a digital bus (ARINC) in a series of binary numbers. These output serves as an input for cockpit instruments, such as the PFD.
  • Types of Computers  Interactive Computers:  The plane crew interfaces with the computer.  Example: Control Display Unit (CDU).  Reference Computers:  Provides information used by other computers.  Example: Inertial Reference System. (IRS – calculates airspeed, heading, attitude etc.). Information is provides to other systems, such as Auto-throttle computer, FMC etc.
  • Types of Computers  Storage Computers:  Store information such as flight roots, total fuel, overspeed threshold, etc.  Controlling Computers:  Control a specific device.  e.g. Flap Electronic Unit (FEU). Takes input from the Flap Lever and gives input to the mechanism that extends or detracts the flaps, when the airspeed is within the allowable values.  Informational Computes:  Provide information to the crew.  e.g. ECAM (Electronic Centralized Aircraft Monitoring).
  • A/D & D/A Converters  Temperature is an analogue value. It must be converted to discrete value, to be displayed in a digital computer.  The user input signal to drive a flight control surface is digital. However, the signal that will drive the control surface must be analog.
  • D/A Converters  The circuit is called “Binary Weighted Ladder”. 3-bit Digital Input Analog Output
  • A/D: Sampling  Resolution of A/D conversion depends on:  Sampling rate  Number of bits used in conversion and output voltage range.  An mp3 of 44000HZ and 192kbps.  Sampling rate: 44000 samples per sec.  192Kbps: Affects the size of the discrete areas.
  • D/A & A/D Converters Specifications  Accuracy:  The actual output vs. the converted output.  E.g. if the maximum output of the converter is 10V and the error is ±1%, then the maximum error for any voltage output is 10mV.  Resolution of A/D converters:  The number of steps the input is divided into. Is expressed in power of 2. A 12-bit A/D converter divides the analog signal in 212 steps.  Sample and Hold A/D converters:  Freezes the analog input at the moment a new sample is taken.  Throughput:  The maximum number of bits “produced” or “consumed” per second (the bit rate).