Analog scope quality, price, and performance?

L

Lance Morgan

Guest
There's a wide variation in new and used analog scope prices, and
perhaps the usually 'you get what you pay for' applies

How does a new entry level 2 ch 20MHz $400 compare to a higher BW $700
model? How much $$ goes for increased BW?

I use older, seemingly good working order, low BW scopes for
automotive work. Adjusting everything as best and as much as possible
(to my intermediate knowledge), using different X10 probes, various
probe lead routings, I can only see the saturation injector waveform
(goes to near ground to activate the injector) @ 2ms Time/DIV (the
injector PW spec is [coincidentally?) 2.2ms, which is what I see w/the
trace at just over 1 grid. If I sweep faster (which I want to do) or
slower, I get ga ga. With most of the other auto components, I have no
problem at faster time bases

Would a low-current inductive probe/clamp help (understanding a
different waveform sample must be referenced)?

Would a higher end scope, presumably with better (and/or more
durable?) internal components, have a more flexible trigger, or
'sensitivity' in the generic sense? Or how might higher end scopes
perform better (better CRT? etc.)Other thoughts or suggestions?

Thank you,
Lance
 
On 19 Mar 2004 11:25:21 -0800, alancemor@yahoo.com (Lance Morgan)
wrote:

There's a wide variation in new and used analog scope prices, and
perhaps the usually 'you get what you pay for' applies
Have you checked e-bay?

How does a new entry level 2 ch 20MHz $400 compare to a higher BW $700
model? How much $$ goes for increased BW?
Look for a decent Tektronix with a delayed sweep capability.

I use older, seemingly good working order, low BW scopes for
automotive work. Adjusting everything as best and as much as possible
(to my intermediate knowledge), using different X10 probes,
Properly compensated? Do you know how to compensate a probe?

various
probe lead routings, I can only see the saturation injector waveform
(goes to near ground to activate the injector) @ 2ms Time/DIV (the
injector PW spec is [coincidentally?) 2.2ms, which is what I see w/the
trace at just over 1 grid. If I sweep faster (which I want to do) or
slower, I get ga ga.
You're on internal synch I presume?
You'd be better off synching from another cylinder and using delayed
sweep to look at the one you're interested in.

With most of the other auto components, I have no
problem at faster time bases
Automotive events are a rather leisurely as far as a scope is
concerned, but the environment is noisy.

Would a low-current inductive probe/clamp help (understanding a
different waveform sample must be referenced)?
By way of external synch.

Would a higher end scope, presumably with better (and/or more
durable?) internal components, have a more flexible trigger, or
'sensitivity' in the generic sense?
More selectable. Leading edge, trailing edge, positive going, negative
going, level set, channel selectable etc.

Or how might higher end scopes
perform better (better CRT? etc.)
Wider bandwidth, delated sweep, multiple input channels, event
capture...

Other thoughts or suggestions?
If you do get a better scope, you're on a learning curve finding how
to make use of its capabilities. Just twiddling knobs to see what
happens can get you lost real quick. Find an experienced electronics
tech to give you lessons or at least consult a good text on the
subject.
 
In article <2a52f3e9.0403191125.43be2305@posting.google.com>,
Lance Morgan <alancemor@yahoo.com> wrote:
There's a wide variation in new and used analog scope prices, and
perhaps the usually 'you get what you pay for' applies
It does, but the depreciation on used equipment may be larger than you
expect. You can buy a used scope for $100 which will have the same
features and quality as a new one for $600. If you're buying one-offs
for yourself and don't need to supply a company or lab with identical
units, used is almost certainly the way to go. (Note that this is
specific to analog; the situation for digital is somewhat different, and
is not covered here)

Obviously bandwidth affects price. However, the more expensive models
also add features.

Any scope made more recent than tubes will probably have at least 20 MHz
bandwidth, two channels, and the ability to trigger off of either
channel on the rising or falling edge. It will probably have a third
channel that can also be used to trigger, but may not be displayble.
Triggering can be "normal", "auto" (sweeps even if trigger is absent),
and "single" (one sweep, then you press the reset button). There will
be an "add" mode, and a "channel 2 invert" mode, which can be used
together to display a single differential signal without putting your
oscilloscope on an isolation transformer. There will also be an X-Y
mode.

Moving up in price, the most significant feature that you gain is more
sophisticated triggering. You'll likely get to select lowpass and
highpass filters on the trigger (not of adjustable frequency, but still
useful), holdoff, and delayed sweep. I don't end up using the filtering
much myself, but I use the holdoff and delayed sweep quite a lot.

Moving up more, you then get cursors with readouts which will give you
time and voltage measurements. Scopes with these cursors,
unfortunately, are hybrid analog/digital designs, and may be less
reliable than a pure analog scope, making them less desirable used.
This particularly applies to the Tektronix 24xx series, which are
infamous for a common failure mode involving a no-longer-made
proprietary IC. As for other features, you may also get three or four
real channels which can be displayed, possibly with a full range of
voltage scaling or possibly with only a partial set of options.

Higher bandwidth scopes tend to also have more features, but in the
middle of the range (around 100-200 MHz bandwidth) you will often be
able to choose more bandwidth *or* more features for the same price
increase.

There are other random features you may see, like a "Z" input which
modulates intensity (useful mainly in X-Y mode). I've never used it for
much, but I've seen a web page of somebody who's displayed old Atari
games with vector output on his oscilloscope with it! Some
oscilloscopes may output a ramp voltage from somewhere in the sweep
circuit (useful for kluging a spectrum analyzer-like display on your
scope). One of mine has gate outputs from the trigger, which I can
connect to a counter for precise timing measurements. I don't think the
presence or absence of these tend to correlate strongly with price,
they're just rather random, so look for them specifically if you want
them.

trace at just over 1 grid. If I sweep faster (which I want to do) or
slower, I get ga ga. With most of the other auto components, I have no
Does it fail to trigger at all, or does it trigger at different parts of
the waveform such that you see unintelligible overlaid signals from each
sweep? I'd suggest trying a single-sweep with it set faster and see if
you see something which makes sense. If it *is* triggering, but is
triggering at different places once you turn the time faster than 2
ms/div, then upgrading to a scope which has trigger holdoff might be
just the thing.

As a short-term approach to see more detail in the signal, set it to 2mS
where it works, and see if you have a 10x multiplier button for the
timebase (it may also be achieved by pulling on the knob). This will
make it display as if it were set to 200uS, while keeping the same
triggering behavior; you may have to turn up the intensity to compensate
for the decreased display time.
 
terran@mit.edu (Terran Melconian) wrote in message news:<c3gk7f$6md$1@means.mit.edu>...
In article <2a52f3e9.0403191125.43be2305@posting.google.com>,
Lance Morgan <alancemor@yahoo.com> wrote:
There's a wide variation in new and used analog scope prices, and
perhaps the usually 'you get what you pay for' applies

It does, but the depreciation on used equipment may be larger than you
expect. You can buy a used scope for $100 which will have the same
features and quality as a new one for $600. If you're buying one-offs
for yourself and don't need to supply a company or lab with identical
units, used is almost certainly the way to go. (Note that this is
specific to analog; the situation for digital is somewhat different, and
is not covered here)

Obviously bandwidth affects price. However, the more expensive models
also add features.

Any scope made more recent than tubes will probably have at least 20 MHz
bandwidth, two channels, and the ability to trigger off of either
channel on the rising or falling edge. It will probably have a third
channel that can also be used to trigger, but may not be displayble.
Triggering can be "normal", "auto" (sweeps even if trigger is absent),
and "single" (one sweep, then you press the reset button). There will
be an "add" mode, and a "channel 2 invert" mode, which can be used
together to display a single differential signal without putting your
oscilloscope on an isolation transformer. There will also be an X-Y
mode.

Moving up in price, the most significant feature that you gain is more
sophisticated triggering. You'll likely get to select lowpass and
highpass filters on the trigger (not of adjustable frequency, but still
useful), holdoff, and delayed sweep. I don't end up using the filtering
much myself, but I use the holdoff and delayed sweep quite a lot.

Moving up more, you then get cursors with readouts which will give you
time and voltage measurements. Scopes with these cursors,
unfortunately, are hybrid analog/digital designs, and may be less
reliable than a pure analog scope, making them less desirable used.
This particularly applies to the Tektronix 24xx series, which are
infamous for a common failure mode involving a no-longer-made
proprietary IC. As for other features, you may also get three or four
real channels which can be displayed, possibly with a full range of
voltage scaling or possibly with only a partial set of options.

Higher bandwidth scopes tend to also have more features, but in the
middle of the range (around 100-200 MHz bandwidth) you will often be
able to choose more bandwidth *or* more features for the same price
increase.

There are other random features you may see, like a "Z" input which
modulates intensity (useful mainly in X-Y mode). I've never used it for
much, but I've seen a web page of somebody who's displayed old Atari
games with vector output on his oscilloscope with it! Some
oscilloscopes may output a ramp voltage from somewhere in the sweep
circuit (useful for kluging a spectrum analyzer-like display on your
scope). One of mine has gate outputs from the trigger, which I can
connect to a counter for precise timing measurements. I don't think the
presence or absence of these tend to correlate strongly with price,
they're just rather random, so look for them specifically if you want
them.

trace at just over 1 grid. If I sweep faster (which I want to do) or
slower, I get ga ga. With most of the other auto components, I have no

Does it fail to trigger at all, or does it trigger at different parts of
the waveform such that you see unintelligible overlaid signals from each
sweep? I'd suggest trying a single-sweep with it set faster and see if
you see something which makes sense. If it *is* triggering, but is
triggering at different places once you turn the time faster than 2
ms/div, then upgrading to a scope which has trigger holdoff might be
just the thing.

As a short-term approach to see more detail in the signal, set it to 2mS
where it works, and see if you have a 10x multiplier button for the
timebase (it may also be achieved by pulling on the knob). This will
make it display as if it were set to 200uS, while keeping the same
triggering behavior; you may have to turn up the intensity to compensate
for the decreased display time.
Thanks for the response. My leading sentence was probably misleading,
as basically I'm after what upper-level scope build quality or
features (used or new [I buy good used]) would or might allow a
clearer display of a difficult to see signal (at least on 3 different
scopes, so far).

Since it's just auto apps, low BW is fine, and I can look for quality
or features over higher BW. So far I've used older B&Ks and Leaders,
w/various combos of Auto and Manual trigger settings, EXT trigger with
an inductive clamp (for ignition analysis [paired with inversion]; not
for the injector PW), adjusting the hold-off, delay, etc until I get
the most interpretable waveform. HF Rej doesn't seem to help. Higher
quality/presumably better shielded probes, and various routing around
the engine bay doesn't help (if noise is a factor)

The injector PW ("batch" injectors, btw, wired in parallel: all fire
at the same time) does (partially?) trigger at speeds other than 2
ms/div, but is unintelligible, regardless of vernier sweep time
control or holdoff settings. The scope is not w/me now - I recall a
10X vertical multiplier figure (not helpful for the inj PW), but there
may also be a push/pull for sweep magnification, which I haven't tried
(but would be about double what I'd like to see, if I'm 'stuck' @ 2
ms/div)

Does "more sophisticated triggering" allow either better innate
triggering ability, and/or more user control settings, for (what
appears to be) difficult to capture signals?

Put another way, does an expensive (new or good used) 20MHz scope
trigger/offer more adjustments/better or more consistent ability to
"grab" or trigger/have better leading or trailing edge
distinction/better display of a difficult signal than a cheap 20 MHz
scope?

Thanks again,
Lance
 
In article <2a52f3e9.0403200801.3b16aeff@posting.google.com>,
Lance Morgan <alancemor@yahoo.com> wrote:
trigger/offer more adjustments/better or more consistent ability to
"grab" or trigger/have better leading or trailing edge
Of all the oscilloscope manufacturers, Tektronix probably has the best
reputation for good triggering - not for having more adjustments, but
just for working more reliably and not failing to trigger. I don't have
enough experience to address this in depth, so hopefully someone else
can answer.
 
"mike" <spamme0@juno.com> wrote in message
news:405CF5D0.5010903@juno.com...
Lance Morgan wrote:
terran@mit.edu (Terran Melconian) wrote in message
news:<c3gk7f$6md$1@means.mit.edu>...
[snip]

Can't you buy a tester from an automotive test equipment supplier
designed exactly to show what you're looking for?
If you need to test it, there should be a tester available.
The newer diagnostics built into the engine controller can tell a lot
about the timing or effectiveness of such things as injectors. The
controller turns one injector off at a time and looks for a change in
RPM. which tells it that it's not working if there's no drop in RPM. In
any case, the controller can tell a lot about this stuff, just by using
one of the diagnostic tools that aren't very expensive.

If you try to use a GP scope, you're likely gonna have to build an
external trigger box. If the display is moving all around as the
engine
speed varies, and you want a detailed look, you may have to resort to
a digital storage scope.
If you're adjusting something that's on/off, you might be better off
with a simple PIC or similar processor to display the timing as
numbers
on a readout.
Exactly.

 
mike <spamme0@juno.com> wrote in message news:<405CF5D0.5010903@juno.com>...
Lance Morgan wrote:
terran@mit.edu (Terran Melconian) wrote in message news:<c3gk7f$6md$1@means.mit.edu>...

In article <2a52f3e9.0403191125.43be2305@posting.google.com>,
Lance Morgan <alancemor@yahoo.com> wrote:

snip

Since it's just auto apps, low BW is fine, and I can look for quality
or features over higher BW. So far I've used older B&Ks and Leaders,
w/various combos of Auto and Manual trigger settings, EXT trigger with
an inductive clamp (for ignition analysis [paired with inversion]; not
for the injector PW), adjusting the hold-off, delay, etc until I get
the most interpretable waveform. HF Rej doesn't seem to help. Higher
quality/presumably better shielded probes, and various routing around
the engine bay doesn't help (if noise is a factor)

The injector PW ("batch" injectors, btw, wired in parallel: all fire
at the same time) does (partially?) trigger at speeds other than 2
ms/div, but is unintelligible, regardless of vernier sweep time
control or holdoff settings. The scope is not w/me now - I recall a
10X vertical multiplier figure (not helpful for the inj PW), but there
may also be a push/pull for sweep magnification, which I haven't tried
(but would be about double what I'd like to see, if I'm 'stuck' @ 2
ms/div)

Does "more sophisticated triggering" allow either better innate
triggering ability, and/or more user control settings, for (what
appears to be) difficult to capture signals?

Put another way, does an expensive (new or good used) 20MHz scope
trigger/offer more adjustments/better or more consistent ability to
"grab" or trigger/have better leading or trailing edge
distinction/better display of a difficult signal than a cheap 20 MHz
scope?

Thanks again,
Lance

I'm still not clear on what you're trying to measure.
IN automotive measurements, there are some issues with noise and
high voltage protection. You're also trying to trigger on something
complex and noisy and with a repetition rate lower than the persistence
of the CRT can handle.

Can't you buy a tester from an automotive test equipment supplier
designed exactly to show what you're looking for?
If you need to test it, there should be a tester available.

If you try to use a GP scope, you're likely gonna have to build an
external trigger box. If the display is moving all around as the engine
speed varies, and you want a detailed look, you may have to resort to
a digital storage scope.
If you're adjusting something that's on/off, you might be better off
with a simple PIC or similar processor to display the timing as numbers
on a readout.
mike
I should have posed my questions a bit more clearly, which are, is
there a significant difference in how well a "quality" analog scope
can acquire a difficult pattern vs a low-end scope? If so, is it the
(trigger? or?) design and/or better grade components used and/or
specific, user adjustable features (and experience)?


I use older, used, good working 2 ch analog scopes to keep older (mid
80s to early 90s) cars running. They're quite versatile (and often
times definitive), for testing a multitude of automotive components,
and the real limitations come in not have sample normal waveforms for
reference (some but not all can be researched/found) or just the
experience to distinguish between normal and abnormal patterns. And,
for the most part [;-)], I enjoy using the equipment and learning, and
sometimes! gaining some automotive diagnostic experience

I would love to get a DSO, but the budget won't allow right now. It'd
be especially cool to be able to jpeg or psd some pro techs that try
to help me on occasion, instead of describing the waveforms verbally

The particular problem I'm having is measuring the (batch) fuel
injector Pulse Width. It only recongizably registers @ 2 ms/div - one
grid square on the graticule. I'd like to be able to sweep at faster
time bases, to "stretch out" the PW to more grids, to see more detail
(rapid variation in the PW duration). I'd further like to dual the inj
PW with the O2 sensor (A/F mixture). I'm using the injectors
themselves to synch off of (again, they are wired in parallel in this
case - when one fires the all fire), yet any time sweep above/below 2
ms and I only get a partial trigger, while adjusting various controls
as best a possible. While @ 2 ms/div, the inj PW does properly vary as
take the engine from idle to revved. A low-amp current clamp (dont'
yet have one) might give me more info on the pintle action

I'm using attenuated probes - high voltage, as far as the safety of
the scope goes, is okay.

Noise could be a problem - I've tried to address/alleviate that - and
I think the CRT should be able to handle the inj PW signal

By 'GP scope' - do you mean a general purpose scope or GP-IO
interface?

Anyway, rephrased, do TEKs, Agilents/HPs, LeCroys - whatever
well-regarded analog scopes "see" difficult to acquire patterns
noticably better, more consistently, with more stability and accuracy,
than intermediate, or low-end scopes? Sometimes quality has more to do
with durability than performance (or both). There's usually a fair
number of Hitachis, B&Ks, etc on eBay. And, of course, TEKs at higher
prices (not trying to end this on a name-brand dispute).

Long-winded again (!)
Lance
 
"Watson A.Name - \"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> wrote in message news:<105ql90lbuntqa6@corp.supernews.com>...
"mike" <spamme0@juno.com> wrote in message
news:405CF5D0.5010903@juno.com...
Lance Morgan wrote:
terran@mit.edu (Terran Melconian) wrote in message
news:<c3gk7f$6md$1@means.mit.edu>...
[snip]

Can't you buy a tester from an automotive test equipment supplier
designed exactly to show what you're looking for?
If you need to test it, there should be a tester available.

The newer diagnostics built into the engine controller can tell a lot
about the timing or effectiveness of such things as injectors. The
controller turns one injector off at a time and looks for a change in
RPM. which tells it that it's not working if there's no drop in RPM. In
any case, the controller can tell a lot about this stuff, just by using
one of the diagnostic tools that aren't very expensive.

If you try to use a GP scope, you're likely gonna have to build an
external trigger box. If the display is moving all around as the
engine
speed varies, and you want a detailed look, you may have to resort to
a digital storage scope.
If you're adjusting something that's on/off, you might be better off
with a simple PIC or similar processor to display the timing as
numbers
on a readout.

Exactly.

mike

--
I measure the duty cycle of various components, w/a DMM, as needed.

I use a scope to ck both the component signal output (and ECU signal
input, reference voltage, and grounding of a given component, at the
component, as needed), then see if it matches the I/O at the engine
controller (ECU and/or other control/computer units, either Air/Fuel
etc., or distinct ignition control units), by backprobing at the
controllers. These are pre-OBD II vehicles, but do have some limited
Check Engine Light (more recently MIL, and other) code dx capabililty,
that virtually equal what can be pulled using a scan tool

Thanks again,
Lance
 
"Watson A.Name - \"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com>
wrote in news:105ql90lbuntqa6@corp.supernews.com:

"mike" <spamme0@juno.com> wrote in message
news:405CF5D0.5010903@juno.com...
Lance Morgan wrote:
terran@mit.edu (Terran Melconian) wrote in message
news:<c3gk7f$6md$1@means.mit.edu>...
[snip]

Can't you buy a tester from an automotive test equipment supplier
designed exactly to show what you're looking for?
If you need to test it, there should be a tester available.

The newer diagnostics built into the engine controller can tell a lot
about the timing or effectiveness of such things as injectors. The
controller turns one injector off at a time and looks for a change in
RPM. which tells it that it's not working if there's no drop in RPM. In
any case, the controller can tell a lot about this stuff, just by using
one of the diagnostic tools that aren't very expensive.

If you try to use a GP scope, you're likely gonna have to build an
external trigger box. If the display is moving all around as the
engine
speed varies, and you want a detailed look, you may have to resort to
a digital storage scope.
If you're adjusting something that's on/off, you might be better off
with a simple PIC or similar processor to display the timing as
numbers
on a readout.

Exactly.

mike

--
If he's looking for a scoe for automotive uses,he ought to find a used TEK
THM scope/DMM,one of those small,handheld,LCD digital scopes(5
Mhz,IIRC),they had a set of accessories expressly for automotive apps.


--
Jim Yanik
jyanik-at-kua.net
 
"Lance Morgan" <alancemor@yahoo.com> wrote in message
news:2a52f3e9.0403210814.da2ed50@posting.google.com...
"Watson A.Name - \"Watt Sun, the Dark Remover\""
NOSPAM@dslextreme.com> wrote in message
news:<105ql90lbuntqa6@corp.supernews.com>...
"mike" <spamme0@juno.com> wrote in message
news:405CF5D0.5010903@juno.com...
Lance Morgan wrote:
terran@mit.edu (Terran Melconian) wrote in message
news:<c3gk7f$6md$1@means.mit.edu>...
[snip]

Can't you buy a tester from an automotive test equipment supplier
designed exactly to show what you're looking for?
If you need to test it, there should be a tester available.

The newer diagnostics built into the engine controller can tell a
lot
about the timing or effectiveness of such things as injectors. The
controller turns one injector off at a time and looks for a change
in
RPM. which tells it that it's not working if there's no drop in RPM.
In
any case, the controller can tell a lot about this stuff, just by
using
one of the diagnostic tools that aren't very expensive.

If you try to use a GP scope, you're likely gonna have to build an
external trigger box. If the display is moving all around as the
engine
speed varies, and you want a detailed look, you may have to resort
to
a digital storage scope.
If you're adjusting something that's on/off, you might be better
off
with a simple PIC or similar processor to display the timing as
numbers
on a readout.

Exactly.

mike

--

I measure the duty cycle of various components, w/a DMM, as needed.

I use a scope to ck both the component signal output (and ECU signal
input, reference voltage, and grounding of a given component, at the
component, as needed), then see if it matches the I/O at the engine
controller (ECU and/or other control/computer units, either Air/Fuel
etc., or distinct ignition control units), by backprobing at the
controllers. These are pre-OBD II vehicles, but do have some limited
Check Engine Light (more recently MIL, and other) code dx capabililty,
that virtually equal what can be pulled using a scan tool

Thanks again,
Lance
I have a Q for you. I'm getting a 332 MIL error on my '92 Ranger, and
the rec.auto.tech guys were generous enough to send me the pages that
say it's either the PFE or EGR sensor. I took the one on the wheel well
off and did the test, and it measures okay. But I can't even find the
sensor for the EGR (I forget if it's the airflow, or what it is). The
manual pages show the location for Ford Tempo or some other sideways
engine, not the regular 2.3L 4-cyl in my Ranger. Short of spending a
hundred or more for the shop manuals, where can I get some info on the
location of these sensors specific to my Ranger? Thanks.
 
Lance Morgan wrote:
mike <spamme0@juno.com> wrote in message news:<405CF5D0.5010903@juno.com>...

Lance Morgan wrote:

terran@mit.edu (Terran Melconian) wrote in message news:<c3gk7f$6md$1@means.mit.edu>...


In article <2a52f3e9.0403191125.43be2305@posting.google.com>,
Lance Morgan <alancemor@yahoo.com> wrote:


snip

Since it's just auto apps, low BW is fine, and I can look for quality
or features over higher BW. So far I've used older B&Ks and Leaders,
w/various combos of Auto and Manual trigger settings, EXT trigger with
an inductive clamp (for ignition analysis [paired with inversion]; not
for the injector PW), adjusting the hold-off, delay, etc until I get
the most interpretable waveform. HF Rej doesn't seem to help. Higher
quality/presumably better shielded probes, and various routing around
the engine bay doesn't help (if noise is a factor)

The injector PW ("batch" injectors, btw, wired in parallel: all fire
at the same time) does (partially?) trigger at speeds other than 2
ms/div, but is unintelligible, regardless of vernier sweep time
control or holdoff settings. The scope is not w/me now - I recall a
10X vertical multiplier figure (not helpful for the inj PW), but there
may also be a push/pull for sweep magnification, which I haven't tried
(but would be about double what I'd like to see, if I'm 'stuck' @ 2
ms/div)

Does "more sophisticated triggering" allow either better innate
triggering ability, and/or more user control settings, for (what
appears to be) difficult to capture signals?

Put another way, does an expensive (new or good used) 20MHz scope
trigger/offer more adjustments/better or more consistent ability to
"grab" or trigger/have better leading or trailing edge
distinction/better display of a difficult signal than a cheap 20 MHz
scope?

Thanks again,
Lance

I'm still not clear on what you're trying to measure.
IN automotive measurements, there are some issues with noise and
high voltage protection. You're also trying to trigger on something
complex and noisy and with a repetition rate lower than the persistence
of the CRT can handle.

Can't you buy a tester from an automotive test equipment supplier
designed exactly to show what you're looking for?
If you need to test it, there should be a tester available.

If you try to use a GP scope, you're likely gonna have to build an
external trigger box. If the display is moving all around as the engine
speed varies, and you want a detailed look, you may have to resort to
a digital storage scope.
If you're adjusting something that's on/off, you might be better off
with a simple PIC or similar processor to display the timing as numbers
on a readout.
mike


I should have posed my questions a bit more clearly, which are, is
there a significant difference in how well a "quality" analog scope
can acquire a difficult pattern vs a low-end scope? If so, is it the
(trigger? or?) design and/or better grade components used and/or
specific, user adjustable features (and experience)?


I use older, used, good working 2 ch analog scopes to keep older (mid
80s to early 90s) cars running. They're quite versatile (and often
times definitive), for testing a multitude of automotive components,
and the real limitations come in not have sample normal waveforms for
reference (some but not all can be researched/found) or just the
experience to distinguish between normal and abnormal patterns. And,
for the most part [;-)], I enjoy using the equipment and learning, and
sometimes! gaining some automotive diagnostic experience

I would love to get a DSO, but the budget won't allow right now. It'd
be especially cool to be able to jpeg or psd some pro techs that try
to help me on occasion, instead of describing the waveforms verbally

The particular problem I'm having is measuring the (batch) fuel
injector Pulse Width. It only recongizably registers @ 2 ms/div - one
grid square on the graticule. I'd like to be able to sweep at faster
time bases, to "stretch out" the PW to more grids, to see more detail
(rapid variation in the PW duration). I'd further like to dual the inj
PW with the O2 sensor (A/F mixture). I'm using the injectors
themselves to synch off of (again, they are wired in parallel in this
case - when one fires the all fire), yet any time sweep above/below 2
ms and I only get a partial trigger, while adjusting various controls
as best a possible. While @ 2 ms/div, the inj PW does properly vary as
take the engine from idle to revved. A low-amp current clamp (dont'
yet have one) might give me more info on the pintle action

I'm using attenuated probes - high voltage, as far as the safety of
the scope goes, is okay.

Noise could be a problem - I've tried to address/alleviate that - and
I think the CRT should be able to handle the inj PW signal

By 'GP scope' - do you mean a general purpose scope or GP-IO
interface?

Anyway, rephrased, do TEKs, Agilents/HPs, LeCroys - whatever
well-regarded analog scopes "see" difficult to acquire patterns
noticably better, more consistently, with more stability and accuracy,
than intermediate, or low-end scopes? Sometimes quality has more to do
with durability than performance (or both). There's usually a fair
number of Hitachis, B&Ks, etc on eBay. And, of course, TEKs at higher
prices (not trying to end this on a name-brand dispute).

Long-winded again (!)
Lance
Better scopes trigger better. More accurately, less jitter, higher
bandwidth. Any triggered sweep scope should be good enough for the
bandwidth you need.
You need a vertical delay line to see the trigger event. Most any
reasonable scope will have that.
Without a delay line, the measurement will be minimally affected at
these speeds, but not seeing the trigger event means that you have to
assume that it's triggered in the right place.

Dual sweep makes a useful addition. You can trigger on one thing and
look at something later. But the jitter in rotating machinery makes
this technique much less useful.

You need higher sweep rates at low rep rate. That's solved by a DSO.
As is your desire to capture traces.

Your problem is trigger functionality, not quality. First thing I'd do
is take a PIC processor and build a trigger recognizer that monitors
multiple points and uses logic and timing to generate a stable trigger for
your scope. Next, I'd do some timing calculations and spit out numbers.
At these speeds, you can just about acquire the signal you want using
the A/D built into the PIC. Spit it out the RS-232 port and display it
on your PDA. PIC may not be the optimum microcontroller for this
application, it's just the one I have experience with.

mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
Yaesu FTV901R Transverter, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
alancemor@yahoo.com (Lance Morgan) wrote in message news:<2a52f3e9.0403191125.43be2305@posting.google.com>...

How does a new entry level 2 ch 20MHz $400 compare to a higher
BW $700 model? How much $$ goes for increased BW?

I use older, seemingly good working order, low BW scopes for
automotive work. Adjusting everything as best and as much as
possible (to my intermediate knowledge), using different X10
probes, various probe lead routings, I can only see the
saturation injector waveform (goes to near ground to activate
the injector) @ 2ms Time/DIV (the injector PW spec is
[coincidentally?) 2.2ms, which is what I see w/the trace at
just over 1 grid. If I sweep faster (which I want to do) or
slower, I get ga ga. With most of the other auto components,
I have no problem at faster time bases

Would a low-current inductive probe/clamp help (understanding a
different waveform sample must be referenced)?

Would a higher end scope, presumably with better (and/or more
durable?) internal components, have a more flexible trigger, or
'sensitivity' in the generic sense? Or how might higher end scopes
perform better (better CRT? etc.)Other thoughts or suggestions?
For car use, I don't see any purpose in a more expensive scope, unless
you want digital on-screen displays of voltage and time or storage,
and the cheapest storage scope is probably a PCI or USB scope module
for your computer. I also haven't noticed better triggering with
Tektronix or Fluke than with much cheaper scopes, incluging Hitachi,
Heathkit, and the 35 MHz no-name sold by JDR Microdevices and also
under the Elenco brand, except for a tube scope that had been modified
with a homemade trigger sweep circuit. All of the other scopes had
manual, auto, external, low filter, high filter, and TV vertical and
horizontal trigger modes. Some also had a trigger phase control in
addition to trigger level control, but it never helped me. It's nice
to have dual trace, not only because it lets you compare input and
output signals simultaneously, but also since it almost always
includes chop mode sweep, which helps for low frequency displays.
Another feature you may want is alternate mode triggering, so the
scope can lock onto both signals instead of just one.

All trigger sweep scopes have a trigger delay, but in the cheaper ones
it's a fixed delay of roughly 20-50 ns (length of cable curled up
inside the scope), although that 35 MHz Elenco has a variable delay.

Somebody in sci.electronics.repair may know about fixes for your scope
that will help the triggering.
 

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