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Cathode Ray Oscilloscope

Discussion in 'General Electronics Discussion' started by sairam007, Nov 2, 2010.

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  1. sairam007


    Nov 2, 2010
    Can anyone explain the signals that are displayed in the Cathode Ray Oscilloscope when we touch its probe?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    it's noise
  3. abhitech


    Nov 6, 2010
    disturbance caused in d medium r displayed on d screen
  4. awright


    Oct 10, 2009
    Notice that the preponderance of the noise from touching the probe is a 60 Hz "noisy" waveform. Your body acts as an antenna picking up signals from the electromagnetic pollution that pervades our modern environment. You live your life in this electromagnetic "soup" radiated by the electrical wiring of your house, radio and TV transmitters, industrial facilities, power transmission lines, etc., and the electromagnetic noise that you pick up as an antenna submerged in that soup is conducted to the probe tip that you are touching. If you are not actually touching the probe tip but are just close to it your body burden of noise is conducted to the probe capacitively via the few picofarads between your finger and the probe tip. The "dirtiness" of the predominantly 60 Hz waveform you observe is due to all the non-power line related radiation you are receiving.

    Notice also that if you firmly grasp an earth ground the noise seen on the 'scope diminishes. This is because the signals your body picks up are conducted to ground, diminishing the voltage of the signal on your body. The amount of noise reduction depends upon many factors including your body and skin resistance, the electrical characteristics of the grounded object you are grasping, and the strength of the electromagnetic soup in which you are submerged.

    If you could perform the same observation in an area remote from electromagnetic pollution (or inside a "Faraday Cage" (a fully shielded room)) you would observe greatly reduced "noise" from your body. However, you will never totally eliminate the noise because the entire planet and even the universe is pervaded with some electromagnetic noise, however slight.

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