Oscilloscope

A oscilloscope is a Measuring instrument intended to visualize a electric Signal generally variable during time. It is used by all the Scientifique S in order to visualize either of the electric tensions, or various other physical sizes transformed beforehand into tension by means of an adapted converter.

The analogical oscilloscopes which directly use a multiple of the tension of entry to produce the deviation of the spot and the numerical oscilloscopes are generally distinguished which before transform any treatment the tension of entry of number. Posting either analogical (seldom), or is rebuilt afterwards. It then becomes an additional function of the apparatus which can even be deprived about it, the visualization of the signal being carried out by an external computer connected to the oscilloscope.

Analogical oscilloscopes

This type of apparatus is in process of obsolescence because it generally does not allow that the visualization of tensions Périodique S. It is replaced more and more by the numerical oscilloscopes. We will describe in this paragraph only general information concerning the gauges of tension and the base of time of an analogical oscilloscope.

Inner working of the oscilloscope

The signal to be measured is visualized on a generally green Cathode tube The trace of the oscilloscope is determined by two components: horizontal and a vertical.

  • the component Horizontal E is in Abscisse: it is the Temps, or a tension (mode XY).
  • the component Verticale is in Ordonnée: it is the tension applied by the user.

Mode XY in particular makes it possible to visualize a dephasing between two sinusoidal tensions.

The base of time

The base of time is characterized by a saw tooth voltage applied with the two vertical plates (see diagram).
  • At the same time the electronic gun projects an electron beam between the two plates (the density of the beam corresponds to the luminous intensity):
    • the electric field created by the saw tooth voltage enters the plates
fact of deviating the electrons of their trajectory of origin.
    • the X-coordinate of the new trajectory depends directly on the
value of the saw tooth voltage.
    • So that the user can see this tension, the electrons go
to strike the fluorescent screen of the oscilloscope by producing one light.

Tension applied by the user

  • In the same way that for the base of time, the visualization of the tension
applied to the entry of the oscilloscope by the user is done with the assistance horizontal plates (see diagram) which make deviate the trajectory of electrons vertically.
  • the position in ordinate depends directly on the tension applied by the user.
The base of permanently functioning time, we thus see our tension of entry (amplified before) to evolve/move during time.

Numerical oscilloscopes

Contrary to the analog model the signal to be visualized is beforehand Numérisé by a analog-to-digital Converter (interface A/D). The capacity of the apparatus to post a high signal of Fréquence without Distorsion depends on the quality of this interface. Visualization remains analogical of course.
The main features to be taken into account are:
  • the resolution of the numerical analogical converter.
  • the sampling rate in Mé/s (Mégaéchantillons a second) or Gé/s (Gigaéchantillons a second).
  • the depth memory.

The apparatus is coupled with memories making it possible to store these signals and with a certain number of bodies of analysis and treatment which make it possible to obtain many characteristics of the signal observed:

  • Measurement of the characteristics of the signal: peak value, effective Value, period, Frequency, fast etc
  • Transformation of Fourier who allows to obtain the spectrum of the signal.
  • sophisticated Filtres which, applied to this numeric signal, makes it possible to increase the visibility of details.

The posting of the result is more and more often carried out on a screen with liquid crystals, which makes these apparatuses easy to move and, much less greedy in energy.
The numerical oscilloscopes from now on completely supplanted their analogical predecessors, thanks to their greater portability, a greater facility of use and, especially their reduced cost.

External bonds

  • Philips PM3250 diagram
  • Osqoop Programs free oscilloscope multi-platform (acquisition by port USB)

Simple: Oscilloscope

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