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5. Signal conditioning and transmission

Outline of the lecture
  • Signal conditioning
  • Signal transmission
  • Signal immunity 
Signal conditioning
  1. Sensor conditioning
    1. You have been doing that already. The question is: how does one connect a sensor such that one can measure the influence of what we try to measure.
    2. Voltage divider
      1. Deflection bridge (Wheatstone bridge) (zero-deflection)
      2. Negative feedback
      3. Frequency dependent impedance
    3. Oscillator
    4. Opposite inputs canceling distrubances
  2. Filtering
    1. Passive filter
      1. Low pass filter
      2. High pass filter
      3. Band pass filter
    2. Active filter
    3. Digital filter
  3. Amplification
    1. Transistors
      1. Non-linear
      2. Biasing and coupling (bias removal)
    2. Operational amplifiers
      1. Inverting and non inverting amplifiers
      2. Differential and instrument amplifiers
      3. Summing amplifiers
      4. Integrators
      5. Differentiator
      6. Common rejection
  4. Analog to digital conversion
    1. Stair case relationship with different implementation. Use of comparator.
    2. Additional uncertainty in time (±∆t/2) and in amplitude (±LSB/2).
    3. Sampling frequency
Signal transmission
  1. Voltage transmission
    1. Consider a thermocouple
  2. Current transmission
    1. Conversion
    2. 4mA min. 
      1. (Important side track) Sensor failure detection: it is important to measure correctly or at least provide a confidence level. When a sensor fails, the information is incorrect and the consequences can be a disaster. 
  3. Modulated transmission
    1. Amplitude modulation
    2. Frequency modulation
    3. Pulse width modulation
  4. Digital transmission
    1. Convert the analog signal into a sampled signal and transmit a binary number.
Signal immunity
  1. Electrostatic (capacitive) coupling

  2. Electromagnetic (inductive) coupling
  3. Multiple earth (galvanic) coupling
  4. Solutions
    1. Distance and twisted pairs
    2. Screening and shielding
    3. Single grounds