basic oscilloscope question

[Ken Williams]

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?

 

[att]

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.

 

[1PW]

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?

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.

<http://en.wikipedia.org/wiki/Oscilloscope>

<https://www.cs.tcd.ie/courses/baict/bac/jf/labs/scope/>

<

>

The newer oscilloscopes offered today have mind boggling capabilities
that are well beyond the scope of your question.

Pete

 

[Don Stauffer]

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?

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.

 

[Rich Webb]

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?

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?).

 

[Ken Williams]

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

 

[Rich Webb]

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?

For looking at audio frequency waveforms, something like Daqarta
http://www.daqarta.com/ might be more appropriate. It uses your sound
card for input so it won't go down to DC and nor handle signals much
above the audio range but within those limitations it's good value.

In general, PC/USB o'scopes don't have the real-time sampling rate
necessary to compete with a general purpose scope. Bitscope
http://www.bitscope.com/ has been doing PC/USB scopes for longer than
most and would be on anybody's list that category.

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.

 

[JeffM]

[...]
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[...]

More commonly to electrostatic deflection *plates*.

[...]
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.

....and when the data is stored in semiconductor memory,
you can actually "back up" the display
to points in time BEFORE the trigger point.

 

[krw]

[...]
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[...]

More commonly to electrostatic deflection *plates*.

[...]
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.

...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.

 

[1PW]

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?

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

 

[Ken Williams]

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.
[email protected]

 

[Jamie]

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

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..

http://www.sharewaresoftware.org/sndscopepro/sndscopepro.htm

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.


http://webpages.charter.net/jamie_5"

 

[1PW]

The problem is I don't know what I need or what I'm doing.

Get in line Ken. We all feel like that in the beginning.

How would I generate a 12V 1500Hz wave to pulse a coil. Does a Signal
Generator do that?

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

pulsed with an oscilloscope (hence my oscilloscope questions). It would
be a sine wave I imagine.

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.

<http://us.fluke.com/usen/products/Fluke+170.htm?catalog_name=FlukeUnitedStates>

Of course lesser meters from Fluke's competitors will work adequately
too. If great accuracy is unimportant, many DMMs would do the job.

I use nothing right now, I'm just an idiot
with too many questions.

Perhaps in a short time you'll be the expert.

Thanks.
[email protected]

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

 

[westom]

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.

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.

 

[Don Stauffer]

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?

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.

 

[JeffM]

Doesn't have to be semiconductor memory.
Delay lines have been used in scopes for decades.

~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.

 

[krw]

~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.

 

[Jasen Betts]

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?

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.

 

[Ken Williams]

Hello Ken:

What are your budget limitations? What is the source of the 1500Hz?

There is no real budget, money is no object. I ordered a USB scope
(http://www.darkwire.com.au/html/dso-2090_usb.html) so I can watch it on
my laptop, I liked that idea. The source of the 1500 Hz will probably
be a Signal Generator to start with. For example I generate a signal
with the Signal gen. then watch it with my usb scope. Kind of
uneventful I know.

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?

All this is unknown, I just want to hook this stuff up to see how far I
get.

Would using older/used test equipment be agreeable with you? How much
accuracy (in terms of amplitude and timing) do you require?

Newer is probably better. Nothing has to be very accurate.

to measure different types of distortion as well? What do you use now?

I use nothing and have no need to measure distortion.

 

[westom]

All this is unknown, I just want to hook this stuff up to see how far I
get.

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.