Can someone tell me what an oscilloscope is in plain English? For example is an oscilloscope simply is a device that takes a sampling of the changing voltage/current over a small time frame like 1 millisecond and plots it on a graph. Usually the resulting graph is a sine wave which is AC current.
Correct?
Close. An oscilloscope is a device that will show you the voltage of a signal over a period of time that you select, anywhere from 1 microsecond or less to several seconds, as a glowing line on a screen.
On 02/25/2009 07:59 PM, Ken Williams sent:
Hello Ken:
You're sort of on the right track, but... voltage, not current. The time "frame" can be anything from many seconds down to nanoseconds and better. The resulting /trace/ will be anything from a constant D.C. level (horizontal line) to the narrowest spike of a pulse.
The newer oscilloscopes offered today have mind boggling capabilities that are well beyond the scope of your question.
Pete
-- 1PW @?6A62?FEH9:DE=6o2@=]4@> [r4o7t]
While many modern scopes do "sample", the classic oscilliscope continuously viewed the signal. It had a means to sychronize the display so you could see a repetitive waveform. That way you could view one or more cycles of that repetitive wave. So you viewed what appeared to be a narrow time window, but you were watching it continually. If the amplitude varied, the display sort of jittered a lot.
By contrast, sampling scopes (more expensive than non-sampling) did show JUST what happened during an interval of time, even if the amplitude is changing. It would show, for instance, a transient signal.
Think of an o'scope as just being a voltmeter that can respond to changes in voltage really, really quickly.
Instead of using the measured voltage to deflect a moving needle, as an analogue voltmeter would do, the deflection is applied to coils that steers an electron beam. That's what makes it fast; it's only moving tiny electrons and not the mass of a needle. For the sake of argument, say that the coils move the beam UP for a positive voltage, and DOWN for a negative one.
Now, if one simultaneously deflects that electron beam left to right across a phosphorescent screen, the resulting glow will paint a picture of how voltage is changing with respect to time.
That's really all an analogue o'scope is. You'll be able to change the vertical (voltage) sensitivity to look at signals of different voltage ranges and vary how quickly the beam is swept across the screen to see quickly or slowly changing signals.
The "trigger" just says: Wait until a voltage that I set is seen before starting the sweep (time) across the screen. That helps a lot in looking at repeating waveforms or starting at a desired spot in a wave train.
Digital o'scopes sample the voltage and display dots on the screen instead of steering an electron beam but the behavior, for the most part, mimics analogue scopes: vertical = voltage, horizontal = time.
To complicate matters, many scopes allow one voltage channel to be applied to the Y-axis (vertical) and a second to the X-axis (horizontal). This is "X-Y" mode (clever, eh?).
-- Rich Webb Norfolk, VA
does anyone recommend a normal scope or a PC/USB scope? any recommendations?
also if I wanted a scope to watch a waveform of 1500 Hz is that doable on most scopes?
Ken Williams wrote:
For looking at audio frequency waveforms, something like Daqarta
In general, PC/USB o'scopes don't have the real-time sampling rate necessary to compete with a general purpose scope. Bitscope
WRT "normal" scopes, that's kind of like asking "What kind of car should I get?" It depends on what you'll be using it for; a used Civic and a new Maserati are both entirely appropriate solutions for some problem domain.
-- Rich Webb Norfolk, VA
More commonly to electrostatic deflection *plates*.
...and when the data is stored in semiconductor memory, you can actually "back up" the display to points in time BEFORE the trigger point.
Doesn't have to be semiconductor memory. Delay lines have been used in scopes for decades.
On 02/26/2009 11:53 AM, Ken Williams sent:
Hello Ken:
What are your budget limitations? What is the source of the 1500Hz? What is the usual amplitude (voltage) of the signal? Is it a sine wave or could it be anything? How frequently would you observe the waveform? Would using older/used test equipment be agreeable with you? How much accuracy (in terms of amplitude and timing) do you require? Do you need to measure different types of distortion as well? What do you use now?
Yes. Any ordinary scope can display a waveform with that frequency. New fangled sampling scopes would probably be an incredible overkill for you. Something tells me you wouldn't need to pay much more than $100USD for what you desire.
If you can provide more user information, we can help you that much more.
Pete
-- 1PW @?6A62?FEH9:DE=6o2@=]4@> [r4o7t]
The problem is I don't know what I need or what I'm doing.
How would I generate a 12V 1500Hz wave to pulse a coil. Does a Siginal Generator do that? I would then like to measure/verify what I just pulsed with an oscilloscope (hence my oscilloscope questions). It would be a sine wave I imagine. I use nothing right now, I'm just an idiot with too many questions.
Thanks. snipped-for-privacy@yahoo.com
1PW wrote:
Yes, but you can most likely find a sound card program that can do that for you with out buying anything. The sound card in your computer can record at that frequency and thus programs are out there that show a scope like display for you to analyze it..
remember that you'll need to scale a signal to your sound card. you don't want to drive it with nothing more then a .5.. 1 Vpp.
On 02/26/2009 02:55 PM, Ken Williams sent:
Get in line Ken. We all feel like that in the beginning. :-)
Depending on how much power you wish to deliver to the coil, a qualified yes. Signal generators can also deliver a variable pulse, square wave, triangular wave, sine wave, all continually or in timed bursts, and more.
I would then like to measure/verify what I just
The scope, coil, and signal source, all in a possible parallel fashion is likely what you're looking for. The meagerest oscilloscope will probably suit you fine. But then again, many modern day digital multimeters (DMM) will too. Although pricey, most Fluke DMMs would measure a 1500Hz sine wave with great accuracy while being fairly rugged.
Of course lesser meters from Fluke's competitors will work adequately too. If great accuracy is unimportant, many DMMs would do the job.
Perhaps in a short time you'll be the expert.
Does the coil have more than one winding? What is the application? Do you need to check for shorted turns in the coil's windings? Do you need to confirm the coil's inductance value? Do you need to measure the coil's impedance?
Let us know what you're doing Ken. We are a helpful bunch here.
Pete
-- 1PW @?6A62?FEH9:DE=6o2@=]4@> [r4o7t]
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Your choice of words causes confusion. Either you want a signal generator to apply a repetitive signal, or something to pulse the coil
- one shot. If the wave is continuous (repetitive) and low frequency, then even a multimeter would measure the resulting voltages (or currents). However if pulsing a coil (ie discharging a capacitor into the coil), then an oscilloscope that can display a one-shot signal is necessary.
Obviously, if using a signal generator, then the oscilloscope is also useful (and can display additional useful information).
One example of a low frequency signal generator (as another noted) is the output from a sound card. Further useful are other type of signals. Sine waves applied at different frequencies can be most useful. Also a very narrow pulse can provide useful facts. Sometimes a most crude, inexpensive, and simple signal generator (square waves output by the famous 555 chip) might be sufficient.
Before anyone can answer, first define the problem; what you want to learn. No useful answers because your posts short your help of necessary facts. An objective such as what is your intent or question.
Yes, 1500 Hz is within the bandwidth of virtually any scope on the market these days, even the cheapest. In fact, if you can buy a used Heathkit or Eico, these can handle that easily. Most any scope can handle the entire audio range.
Some of the cheaper ones cannot handle DC, but you don't ordinarily worry about that much. The very low frequency response is actually more of a problem than the audio region. Some cheap scopes will not work well below maybe 50 Hz.
krw wrote:
~100ns of extra data is nice, but a block of pre-trigger data that is proportional to the sweep speed (say 10ms/div) is REALLY cool.
True, scopes have become logic analyzers with analog front ends. Some signal delay after trigger is essential or one can't view the signal that caused the trigger.
even the cheapest benchtop oscilloscope, or a oscilloscope made from an old TV, or the kind that plugs into a computers audio input jack will have no problems with a 1500Hz waveform.
the only sort of scope that would have trouble with that is the medical kind (like they they use for EKGs)
for signals below 10hHz I'd cosnsider a computer soundcard based scope a good staring point, if nothing else it can be a cheap way to learn what you need from your scope.
There is no real budget, money is no object. I ordered a USB scope
All this is unknown, I just want to hook this stuff up to see how far I get.
Newer is probably better. Nothing has to be very accurate.
I use nothing and have no need to measure distortion.
But again, first define the problem; what you want to learn. Few useful answers because your posts was short of necessary facts. An objective such as your intent or question. Amazing how much information is 'hidden' when using a signal generator and a scope if you don't know what to look for. Also useful is a pulse generator or square wave with the scope.
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