Oscilloscopes
- Thread startermbenonis
- Start date
coldnorth57
Active Member
How oscilloscopes work: all about analog, digital, CRT, LCD and USB oscopes
Check this out hope it helps.
Check this out hope it helps.
I was actually hoping for someone to explain it here instead of linking off somewhere.I'm curious how much folks know about older, but fundamental technology.
I was an electronic technician in the Navy (1977 - 1983) so I can tell you in gory detail exactly how an oscilloscope works. However, as I'm also a CB moderator, I'm going to back off and let someone else answer.
I assume you're talking about a CRT oscilloscope.
Around the CRT, there are two sets of coils, the deflection coils. The horizontal coils are driven by the sweep generator, the vertical coils are driven by a preamplifier of some sort that modulates the voltage to the coil based on the input (the signal to be displayed). The magnetic field created by the deflection coils will impose a force upon a charged particle, in this case electrons, emitted by the electron gun.
The electron gun is located at the back end of the CRT. By thermionic emission, it emits electrons which are accelerated by a potential difference, often of several thousand volts. These electrons travel to the other end of the tube, and depending on the voltage and hence the magnetic field created by the deflection coils, will strike the screen in a certain place.
The screen is coated on the inside with a certain phosphor, a coating that emits light when struck by electrons.
The horizontal deflection coils are driven by the sweep generator, which can either produce its own sweep signals, derive them from the AC line, or optionally from another source. These coils move the beam of electrons sideways, across the screen.
The vertical deflection coils are driven by the input amplifier. They move the beam of electrons up and down.
Multi-trace oscilloscopes operate the same way, except for the fact that the traces are multiplexed in some way. There are two ways that I know of. The first is to display the signals sequentially, but applying a DC bias to each successive signal so it appears on the screen above or below another.
The other method is to rapidly switch back and forth between the two signals, at such a frequency that the switching is not visible to the eye.
The first oscilloscopes used vacuum tubes, requiring extra rails from the power supply, as well as regular maintenance when the filaments burned out. The (relatively) few CRT oscilloscopes still in production use solid-state components.
The result of this is that the signal appears on the screen, in a graph of voltage with respect to time, or if the unit is set differently, with a different voltage.
Around the CRT, there are two sets of coils, the deflection coils. The horizontal coils are driven by the sweep generator, the vertical coils are driven by a preamplifier of some sort that modulates the voltage to the coil based on the input (the signal to be displayed). The magnetic field created by the deflection coils will impose a force upon a charged particle, in this case electrons, emitted by the electron gun.
The electron gun is located at the back end of the CRT. By thermionic emission, it emits electrons which are accelerated by a potential difference, often of several thousand volts. These electrons travel to the other end of the tube, and depending on the voltage and hence the magnetic field created by the deflection coils, will strike the screen in a certain place.
The screen is coated on the inside with a certain phosphor, a coating that emits light when struck by electrons.
The horizontal deflection coils are driven by the sweep generator, which can either produce its own sweep signals, derive them from the AC line, or optionally from another source. These coils move the beam of electrons sideways, across the screen.
The vertical deflection coils are driven by the input amplifier. They move the beam of electrons up and down.
Multi-trace oscilloscopes operate the same way, except for the fact that the traces are multiplexed in some way. There are two ways that I know of. The first is to display the signals sequentially, but applying a DC bias to each successive signal so it appears on the screen above or below another.
The other method is to rapidly switch back and forth between the two signals, at such a frequency that the switching is not visible to the eye.
The first oscilloscopes used vacuum tubes, requiring extra rails from the power supply, as well as regular maintenance when the filaments burned out. The (relatively) few CRT oscilloscopes still in production use solid-state components.
The result of this is that the signal appears on the screen, in a graph of voltage with respect to time, or if the unit is set differently, with a different voltage.
There are very few scopes that use magnetic deflection (not counting the ones that are PC-based and have a regular monitor in the box). CRT scopes mainly use electostatic deflection, with two pairs of metal plates at right angles to the beam. A voltage applied to the plates attracts (the positive side) and repels (the negative side) the electron beam. Otherwise, they work as headcrab described.
Nowdays, scopes are just fancy PCs with fast analog-to-digital converters at the front end, and lots of fast memory.
/mike
Nowdays, scopes are just fancy PCs with fast analog-to-digital converters at the front end, and lots of fast memory.
/mike
Yep. I was a Nuke. And I've got a ton of Sea Stories I could tell you, but they're probably still classified...
... And I've got a ton of Sea Stories I could tell you, but they're probably still classified...
I can neither confirm nor deny that! I cheated and did the distance learning through Tom Ed for my BS with a traditional AS..Engineering to back it up.
I still scare my step kids with some of my sean antics.
Have a Fine Navy Day!
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