5.3 Data conversion
- 1. Module 5: Digital Techniques and Electronic Instrument Systems 5.3 Data Conversion
- 2. 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
- 3. 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
- 4. Digital circuits advantages 4 High reliability Easy design High flexibility Easy storage
- 5. 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.
- 6. 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.
- 7. 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).
- 8. 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.
- 9. D/A Converters The circuit is called “Binary Weighted Ladder”. 3-bit Digital Input Analog Output
- 10. 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.
- 11. 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).
Editor's Notes
- #3: Αναλογικά σήματα που υπάρχουν στη φύση:Το φως του ήλιου κατά τη διάρκεια της ημέρας Η θερμοκρασία κατά τη διάρκεια της ημέρας Ο ήχος
- #4: Συσκευές με αναλογικά κυκλώματα:Η κουζίνα (εναλλασσόμενο ρεύμα – θερμοκρασία του ηλεκτρικού ματιού)Ηλεκτρικό καλοριφέρΠίνακας της ΔΕΗΗχεία
- #5: 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.