Mod 8 Unit 1

TIMING

• APPARENT SOLAR TIME

  • Based off the apparent location of the sun

  • Sundials help us use location of sun to give time of day

  • LEAST ACCURATE TIMING MEASURE
    
    

• QUARTZ OSCILLATORS (Crystal Oscillators)

  • Resonating tuned voltage through crystal and result is resonated frequency 

  • Called Piezoelectric effect 

  • Accuracy and stability are affected by temperature and age, causing drift 

  • Require periodic calibration to stay precise 

  • Quartz are the least accurate of oscillators
    
    

• ATOMIC OSCILLATORS

  • Use atom molecules 

  • Release radiation that can be utilized as timing 

  • Not impacted by age or temperature 

  • Two most common types of atomic oscillators are cesium beam oscillator and rubidium gas oscillator
    
    

• CESIUM STANDARD

  • Atomic resonance is 9.192 GHz (9,192 MHz)

  • Created by passing cesium metal through high heat 

  • Highly stable and drift only 200 NANOSECONDS in 24hrs

  • MORE ACCURATE THAN RUBIDIUM 

  • CONSIDERED PRIMARY FREQUENCY STANDARDS
    
    

• RUBIDIUM STANDARD

  • Use Gas cell with resonance of 6.834 GHz (6834 MHz)

  • Drift approximately 1 MICROSECOND every 24 hours 

  • Must be calibrated periodically 

  • SECONDARY FREQUENCY STANDARD

  • ADVANTAGE OVER CESIUM

    • More compact 

    • Lower in cost

    • More power efficient
      
      

• GLOBAL POSITIONING SYSTEM 

  • Used to provide timing standard to our equipment 

  • Accomplished by deploying antenna whose job is to collect timing data from satellites

  • Designed to provide FOUR satellite visibility from anywhere in the world 

  • More Satellites = more accurate timing
    
    

SYNCHRONIZATION

• All nodes need to operate at same clock rate 

• Four standards for synchronization
  
  

  • PLESIOCHRONOUS

    • Does NOT require synchronization between nodes 

    • Provides Highly stable clock at each station
      
      

  • MUTUAL

    • Requires ALL network nodes have their own clocks for timing 

    • Clocks not required to be as precise 

    • Average clock data collected from nodes so all operate off same clock frequency 

    • Network adjust as nodes disconnect and connect

    • Does not pin single point of failure on an unreliable node
      
      

  • MASTER CLOCK

    • Requires one node to be master station 

    • Distributes timing all other stations 

    • Single point of failure

    • Does not scale well with small networks
      
      

  • MASTER SLAVE 

    • MOST RELIABLE SYNCHRONIZATION TECHNIQUE 

    • One node required to be master station

    • Clock signal is distributed to first set of subordinate nodes 

    • Then passed to the next level 

    • MOST ROBUST DUE TO REDUNDANCY

    • All nodes expected to have back up clocks