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Fiber Optics CCTV Transmission Principles & Practice

Learn about analog and digital transmission principles in fiber optics CCTV systems, including intensity modulation and frequency modulation. Explore the benefits and limitations of each method.

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Fiber Optics CCTV Transmission Principles & Practice

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  1. FIBER OPTICS CCTV TRANSMISSIONPRINCIPLES & PRACTICE

  2. 1. Analog Transmission - intensity modulation (IM) - frequency modulation (FM) 2. Digital Transmission transmission of analog video inputs - - transmission of digital video inputs Types of Transmission

  3. Analog Intensity Modulation Transmission Intensity or brightness of fiber optics emitter (LED) is varied in proportion to the level of the incoming signal. Receiver then produces an output which is controlled by the Automatic Gain Control (AGC) to produce an identical output. Tx Fiber attenuation Rx Incoming signal Launched light intensity Received light intensity Outgoing signal AGC

  4. Light o/p - Non-linearity of LED Signal I/p - Electrical Interference (noise) Tx Rx Outgoing signal Incoming signal Bright scene Limitations of Intensity Modulation - Restrictions on signal format due to AGC

  5. Light o/p - Non-linearity of LED Signal I/p - Electrical Interference (noise) Tx Rx Outgoing signal Incoming signal Dark scene Limitations of Intensity Modulation - Restrictions on signal format due to AGC

  6. Analog Transmission- Frequency Modulation Transmitter generates a high frequency carrier signal. Frequency of this carrier is varied according to level of incoming signal. Receiver amplifies and clips (to eliminate AM noise) then demodulates to recover the original signal. Fiber attenuation Tx Rx Incoming signal Launched light intensity Received light intensity Outgoing signal

  7. Benefits of Frequency Modulation • System is less dependent on LED linearity. • Transmission is immune to AM interference. • AGC operation does not restrict signal format. • Multiple carrier frequencies permit two or more signals to be multiplexed on to one fiber. • Can be used for transmission of either analog or data signals, or both.

  8. Digital Transmissionof Analog Signals Transmitter codes incoming signal into a series of 1’s and 0’s for transmission over the fiber. Receiver decodes the recovered 1’s and 0’s into the original signal. Tx Rx Fiber attenuation D A A D Incoming signal Launched light intensity Received light intensity Outgoing signal

  9. Incoming Signal Sampled Signal (at 2x highest frequency) Signal Amplitude 3456789998643113456899875421234578987532112346789 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1001, 1000, 0110, 0100, 0011, 0001, 0001, 0011, 0100, 0101, 0110, 1000, 1001, 1001, 1000, 0111, 0101, 0100, 0010, 0001, 0010, 0011, 0100, 0101, 0111, 1000, 1001, 1000, 0111, 0101, 0011, 0010, 0001, 0001, 0010, 0011, 0100, 0110, 0111, 1000, 1001 Binary Coded Signal Analog to Digital Conversion

  10. Benefits of Digital Transmission • System virtually independent of device linearity. • Total immunity to AM interference. • Receiver AGC is not required. • Signals can be regenerated within repeaters without loss of quality or added noise. • Multiplexed signals can be inserted or extracted with ease.

  11. Limitations of Digital Transmission - Uncompressed video requires very large data rates e.g. 270Mb/s per channel for Rec. CCIR 601 - Until recently effective compression techniques were either very expensive, or unacceptably slow.

  12. Principles of CCTVVideo Transmission

  13. Image Scanning The image is scanned with a series of horizontal lines. At every point, the camera tube converts the image brightness into a proportional electrical voltage. Voltage Peak white 1.0V 0.3V 0V Black level Time

  14. Screen Resolution (625 lines) Active Picture Area 625 lines 575 visible ‘TV lines’ 833 pixels (4:3 aspect ratio)

  15. Video Bandwidth (625 Lines) 833 ‘lines’ wide (4:3 ratio) No. of pixels per frame = 625 x 833 = 520,625 No. of frames per second = 25 Therefore maximum pixel rate = 25 x 520,625= 13,015,625 i.e. 13 Mpixel/s Maximum analogue frequency is only half the maximum pixel rate. 625 lines high Therefore the required video bandwidth is approximately 0.5 x 13 = 6.5 MHz. Standard European TV provides a bandwidth of 5.5 MHz,corresponding to a vertical visible screen resolution of about 485 ‘TV Lines’. This is the bandwidth of a monochrome (B&W) channel.

  16. Encoding Apparatus R Camera G B Transmission Link Lens Dichroic Filters R Decoding Apparatus G B Triple beam Display Tube Color TV Transmission Components

  17. Sync pulses Blue Red Green Blue Red Green R R + Luminance Y G G + + (0 - 5.5 MHz) B B + Chroma C R + (3 - 5.5 MHz) U = R - Y Y - Colour Difference (0 - 1.5 MHz) B + Y V = B - Y - 4.43 MHz Carrier Component Video

  18. Sync pulses Green Blue Red Blue Red Green R R + Luminance Y G G + + (0 - 5.5 MHz) B B + Chroma C R + (3 - 5.5 MHz) U = R - Y Y - Colour Difference (0 - 1.5 MHz) B + Y V = B - Y - 4.43 MHz Carrier Composite Video Composite Video + (0 - 5.5 MHz)

  19. Chrominance (Colour) Signal 4.43 MHz Composite Video Spectrum (PAL) Luminance (B & W) Signal 0 6 MHz

  20. PTZ Camera Video& Telemetry Data

  21. PTZ Camera Monitor T.P. T.P. PTZ Keyboard PTZ Camera Transmission Coax Coax

  22. PTZ Camera F.O. Transmitter F.O. Receiver Monitor F.O. Transmitter F.O. Receiver Optical Fibers F.O. Receiver F.O. Transmitter PTZ Keyboard PTZ Camera Transmission Coax Coax T.P. T.P.

  23. PTZ Camera F.O. Transmitter F.O. Receiver Monitor F.O. Transmitter F.O. Receiver Optical Fiber PTZ Keyboard PTZ Camera Transmission Coax Coax T.P. T.P.

  24. 1300 nm Coax 1300 nm Transmitter PTZ Camera WDM Coupler T.P. 850 nm Receiver 850 nm Single Fiber Bi-directional Transmission Monitor 1300 nm Coax 1300 nm Receiver WDM Coupler T.P. 850 nm Transmitter 850 nm PTZ Keyboard Single Fiber PTZ Transmission

  25. PTZ Data Formats, b.f. (before fiber)

  26. Maximum distance a few metres Logic 1 Line impedance Logic 0 Noise & pick-up TTL Data Transmission Signal Line Tx Rx Earth Return Logic 1 +5 v 0 v Logic 0

  27. RS232 Data Transmission Signal Line Tx Rx Earth Return Maximum distance 15 - 100 metres Logic 1 Logic 1 +15 v 0v -15 v Line impedance +3.0 v -3.0 v Logic 0 Noise & pick-up Logic 0

  28. Tx Rx Tcvr B Tcvr A Gnd Gnd Tx Rx Fiber Options Modem Fiber Options Modem Data in Data out 1 or 2 fibers Gnd Gnd Data in Data out RS232 3-wire Fiber Connections

  29. Signal Line A Signal Line B Twisted Pair Cabling Balanced Line (RS422) Data Transmission +5V 0 Tx +5V 0

  30. Balanced Line Noise Rejection Signal o/p = A - B + 5v +5V 0 + - - 5v +5V 0 Differential Input Receiver Twisted Pair Cabling Noise & Interference

  31. Fiber Options Modem Fiber Options Modem Data out +ve Data in +ve Data in -ve Data out -ve 1 or 2 fibers Data out +ve Data in +ve TxA RxA Data out -ve Data in -ve TxB RxB Tcvr A Tcvr B RxA TxA RxB TxB RS422 4-wire Fiber Connections

  32. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 PTZ Data Network PTZ Controller & Expander

  33. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 PTZ Fiber Network S732DVT fiber(s) S732DVT PTZ Controller & Expander S732DVR S732DVT S732DVR S732DVR

  34. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 PTZ Data Network PTZ Controller & Expander PTZ Controller

  35. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 Databus Network Is this possible ??? PTZ Controller & Expander PTZ Controller

  36. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 Databus Network- outgoing data + - TxA PTZ Controller TxB RxA RxB

  37. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 Databus Network- outgoing data - OK TxA - + PTZ Controller TxB RxA RxB

  38. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 RS422 Databus Network- return data TxA TxA PTZ Controller + - + - + - TxB TxB RxA RxA RxB RxB

  39. PTZ Camera 3 PTZ Camera 2 PTZ Camera 1 RS422 Databus Network- return data TxA TxA PTZ Controller - + + - + - TxB TxB RxA RxA ??? RxB RxB ??? Conflict

  40. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 The solution- tristate RS485 TxA PTZ Controller off off off off off off TxB RxA RxB

  41. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 The solution- tristate RS485 TxA TxA PTZ Controller off off off off - + TxB TxB RxA RxA RxB RxB

  42. PTZ Camera 1 PTZ Camera 2 PTZ Camera 3 The solution- tristate RS485 TxA TxA PTZ Controller off off off off + - TxB TxB RxA RxA RxB RxB

  43. Logic ‘1’ (+5 v) RS422 (bi-state) 0V Logic ‘0’ (-5 v) Logic ‘1’ (+5 v) RS485 (tri-state) ‘off state’ Logic ‘0’ (-5 v) Logic ‘1’ (+5 v) ‘off state’ RS485 (tri-state with offset) Logic ‘0’ (-5 v) RS422 vs RS485 Signal Levels

  44. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller off off off off off off A B

  45. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller RxA RxB RxA RxB RxA RxB TxA TxB

  46. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller RxA RxB RxA RxB RxA RxB TxA TxB

  47. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller off off off off off off A B

  48. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller TxA TxB off off off off RxA RxB

  49. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller TxA TxB off off off off RxA RxB

  50. PTZ Camera 3 PTZ Camera 1 PTZ Camera 2 2-wire RS485 PTZ Controller off off off off off off A B

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