D
David L. Jones
Guest
"sbrehler" <sbrehler@mndspring.com> wrote in message
news:Q4ednWcw4O2fTYzUnZ2dnUVZ_vninZ2d@earthlink.com...
signals. This is real handy for analysing digital signals and capturing
glitches for instance.
But other stuff like easy voltage and frequency measurement, cursors, FFT
display (turns your scope into a spectrum analyser), PC screen capturing etc
are incredibly handy. Once you have them you don't want to go back.
it's silly to use slower than inverse double that in sample rate (2ms). For
simplicity, just say inverse that (or 1ms).
The AutoSet button is handy for beginners here, it sets it all up for you.
Also handy for experts when someone has been dicking around with your scope
setup and you want to measure a signal fast! :->
scopes are the "real time" kind.
Basically, a "real time" scope is one that has the sample rate at least 5 to
10 times faster than the analog bandwidth, with 10 being a prefered minimum.
e.g. a 100MHz analog bandwith "real time" scope will have a 1GS/s sample
rate minimum. The Tektronix TDS-210 started this trend many years ago.
A real time scope means that you can measure the full analog bandwidth
without aliasing and other issues. Also, it means the "single shot
bandwidth" will be equal to the full analog bandwith.
Fast sample memory is expensive though, so some 100MHz models will have say
a 400MS/s sample rate. This is on the low side, but still ok.
Older (and cheaper) digital scopes have what is often called "equivalent
time" sampling. It means the sample rate is slower than the analog
bandwidth. So a 100MHz analog bandwidth scope might commonly have a 20MS/s
sample rate.
This means a high frequency singal will need to be sampled over multiple
trigger points instead of over one sample period ("real time").
In this case the best "single shot" signal you can capture is say (rule of
thumb) 10 times less than the sample rate - or 2MHz - pretty awful for a
"100MHz" scope!
With repetative signals though you can get up to the full analog bandwidth,
but triggering issues can be a pain.
Don't buy a scope like this, although it's hard to find one these days
except in the extreme high bandwidth (>10GHz) end of the market.
The other main importance with digital scopes is the amount of sample
memory. Golden rule is , the more the better, you can never have too much.
Not much choice with very low cost models though, they will typically have
<10KB of memory. This is fine for general use.
Big memory comes in handy for "zooming in" on captured signals. 100KB is
really good, 1MB+ is awesome.
And BTW, don't let anyone talk you into buying a "PC based" digital scope.
They just aren't the same as a proper bench scope.
Dave.
news:Q4ednWcw4O2fTYzUnZ2dnUVZ_vninZ2d@earthlink.com...
Which model(s) are you looking at? We can help you with some advice.
Yep, the main benefit of course is being able to capture single shot
signals. This is real handy for analysing digital signals and capturing
glitches for instance.
But other stuff like easy voltage and frequency measurement, cursors, FFT
display (turns your scope into a spectrum analyser), PC screen capturing etc
are incredibly handy. Once you have them you don't want to go back.
It can do, yes. The better ones have anti-aliasing filters which can help.
Common sense goes a long way here. If you are measuring say a 1KHz signal
it's silly to use slower than inverse double that in sample rate (2ms). For
simplicity, just say inverse that (or 1ms).
The AutoSet button is handy for beginners here, it sets it all up for you.
Also handy for experts when someone has been dicking around with your scope
setup and you want to measure a signal fast! :->
Yes, this used to be an issue but is rarely so these days as most digital
scopes are the "real time" kind.
Basically, a "real time" scope is one that has the sample rate at least 5 to
10 times faster than the analog bandwidth, with 10 being a prefered minimum.
e.g. a 100MHz analog bandwith "real time" scope will have a 1GS/s sample
rate minimum. The Tektronix TDS-210 started this trend many years ago.
A real time scope means that you can measure the full analog bandwidth
without aliasing and other issues. Also, it means the "single shot
bandwidth" will be equal to the full analog bandwith.
Fast sample memory is expensive though, so some 100MHz models will have say
a 400MS/s sample rate. This is on the low side, but still ok.
Older (and cheaper) digital scopes have what is often called "equivalent
time" sampling. It means the sample rate is slower than the analog
bandwidth. So a 100MHz analog bandwidth scope might commonly have a 20MS/s
sample rate.
This means a high frequency singal will need to be sampled over multiple
trigger points instead of over one sample period ("real time").
In this case the best "single shot" signal you can capture is say (rule of
thumb) 10 times less than the sample rate - or 2MHz - pretty awful for a
"100MHz" scope!
With repetative signals though you can get up to the full analog bandwidth,
but triggering issues can be a pain.
Don't buy a scope like this, although it's hard to find one these days
except in the extreme high bandwidth (>10GHz) end of the market.
The other main importance with digital scopes is the amount of sample
memory. Golden rule is , the more the better, you can never have too much.
Not much choice with very low cost models though, they will typically have
<10KB of memory. This is fine for general use.
Big memory comes in handy for "zooming in" on captured signals. 100KB is
really good, 1MB+ is awesome.
And BTW, don't let anyone talk you into buying a "PC based" digital scope.
They just aren't the same as a proper bench scope.
Dave.