# Oscilloscope resolution

J

#### J. Clouse

Jan 1, 1970
0
Hi all,

I'm not new to electronics, but not well versed in scopes.

Just purchased a new Tektronix TDS1001B scope (~$800). In testing a piece of equipment, the 28 KHz (28,000 Hz) ringing on a pulse (about 2 Hz) is not nearly as well defined as it was on our Gould OS4100 (before it broke). In fact the ringing is barely visible at 250 microseconds sweep. The ringing was about 5 % of the pulse height on the Gould at this sweep rate. Do we need a higher sample rate, other than an LCD screen or what to get better detail on the ringing? Thanks. ns J #### Jim Yanik Jan 1, 1970 0 [email protected] (J. Clouse) wrote in Hi all, Help please. I'm not new to electronics, but not well versed in scopes. Just purchased a new Tektronix TDS1001B scope (~$800).
In testing a piece of equipment, the 28 KHz (28,000 Hz) ringing on a
pulse (about 2 Hz) is not nearly as well defined as it
was on our Gould OS4100 (before it broke). In fact the
ringing is barely visible at 250 microseconds sweep.
The ringing was about 5 % of the pulse height on the Gould
at this sweep rate. Do we need a higher sample rate,
other than an LCD screen or what to get better detail
on the ringing? Thanks.

ns

how does your ground connection to the scope probe look?
thats a big source of ringing.

How do the two scopes BW/rise time compare?

J

#### J. Clouse

Jan 1, 1970
0
[email protected] (J. Clouse) wrote in

how does your ground connection to the scope probe look?
thats a big source of ringing.

How do the two scopes BW/rise time compare?

--------------------------------------------------------------

It appears I was a little nondescriptive. We are viewing the
microphone pickup signal from a metal dome loudspeaker tweeter.
It has a mechanical resonance about 28 KHz. We excite this with
the leading edge of a 2 Hz square wave (pulse it), which excites
the ringing at 28 KHz. The scope screen (delayed trace so as
to see the start of the trace) shows a vertical line with the
28 KHz ringing starting at the top and riding on the horizontal
top of the 2 Hz square wave. The 28 KHz signal was clear and
distinct (as a sine wave) on our Gould OS4100 scope before it
broke, but is not nearly as well defined (especially as
the ringing diminishes) on the Tektronik scope. Both scopes
have a vertical resolution of 8 bits. Both scopes were set
to the same horizontal sweep rate of course (250 us). The
problem is we don't know which spec applies to get a higher
resolution, in another digital storage scope.

ns

R

#### Robert Lacoste

Jan 1, 1970
0
J. Clouse said:
--------------------------------------------------------------

It appears I was a little nondescriptive. We are viewing the
microphone pickup signal from a metal dome loudspeaker tweeter.
It has a mechanical resonance about 28 KHz. We excite this with
the leading edge of a 2 Hz square wave (pulse it), which excites
the ringing at 28 KHz. The scope screen (delayed trace so as
to see the start of the trace) shows a vertical line with the
28 KHz ringing starting at the top and riding on the horizontal
top of the 2 Hz square wave. The 28 KHz signal was clear and
distinct (as a sine wave) on our Gould OS4100 scope before it
broke, but is not nearly as well defined (especially as
the ringing diminishes) on the Tektronik scope. Both scopes
have a vertical resolution of 8 bits. Both scopes were set
to the same horizontal sweep rate of course (250 us). The
problem is we don't know which spec applies to get a higher
resolution, in another digital storage scope.

And don't know why you didn't get something close on both scopes, but why
aren't you simply using a 28KHz bandpass filter between your source and the
scope ? This would probably make you life far easier as you could increase
the dynamic range through a gain only in your interesting bandpass, no ?

Cheers,
Robert
www.alciom.com

N

#### nospam

Jan 1, 1970
0
The 28 KHz signal was clear and
distinct (as a sine wave) on our Gould OS4100 scope before it
broke, but is not nearly as well defined (especially as
the ringing diminishes) on the Tektronik scope.

'not nearly as well defined' doesn't really tell us much about what you
think the problem is.

The scope has a sample rate at whatever timebase you are using and is going
to put a pixel on the screen for each sample. I presume the sample rate is
high enough for 28kHz so if it doesn't look like a 28kHz sinewave then
probably the signal isn't a 28kHz sinewave.

Maybe the signal has high frequency noise which the old scope didn't see or
the new scope and earthing arrangement is making the noise worse.

If the scope has a bandwidth limit try it, if it has a glitch capture mode
try that to make the noise more visible. If it has an average mode and your
trigger is stable enough try that to average out noise.
--

J

#### Joerg

Jan 1, 1970
0
J. Clouse said:
--------------------------------------------------------------

It appears I was a little nondescriptive. We are viewing the
microphone pickup signal from a metal dome loudspeaker tweeter.
It has a mechanical resonance about 28 KHz. We excite this with
the leading edge of a 2 Hz square wave (pulse it), which excites
the ringing at 28 KHz. The scope screen (delayed trace so as
to see the start of the trace) shows a vertical line with the
28 KHz ringing starting at the top and riding on the horizontal
top of the 2 Hz square wave. The 28 KHz signal was clear and
distinct (as a sine wave) on our Gould OS4100 scope before it
broke, but is not nearly as well defined (especially as
the ringing diminishes) on the Tektronik scope. Both scopes
have a vertical resolution of 8 bits. Both scopes were set
to the same horizontal sweep rate of course (250 us). The
problem is we don't know which spec applies to get a higher
resolution, in another digital storage scope.

Best to post a screen shot, either on a.b.s.e. or on a web site.

J

#### Jorgen Lund-Nielsen

Jan 1, 1970
0
J. Clouse said:
Hi all,

I'm not new to electronics, but not well versed in scopes.

Just purchased a new Tektronix TDS1001B scope (~\$800).
In testing a piece of equipment, the 28 KHz (28,000 Hz) ringing on a
pulse (about 2 Hz) is not nearly as well defined as it
was on our Gould OS4100 (before it broke). In fact the
ringing is barely visible at 250 microseconds sweep.
The ringing was about 5 % of the pulse height on the Gould
at this sweep rate. Do we need a higher sample rate,
other than an LCD screen or what to get better detail
on the ringing? Thanks.

ns

Some newer scopes have some more noise (CCD-Working Devices)
than older Flash A/D-Converter designs. Maybe the Noise

Jorgen

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