About them 'scope probes

[Jeff Liebermann]

On Fri, 15 Feb 2019 15:33:01 -0800, etpm@whidbey.com wrote:

Below is an answer I gave to Mike about the wave shape and other
features. The description should give you a better idea of what I am
seeing. At least I hope it does.

"Whoops! It looks like the wave is over compensated. So it looks like
at the beginning of the flat waveform it has a little peak that then
drops down to form a flat line for the rest of the wave.

Under compensated or too little capacitance. The overshoot of the
rising part of the square wave means you have too much high frequency
response.

This of
course repeats but in the negative direction for the negative part of
the wave.

Yep. If the negative going part of the waveform were not identical,
then your input square is not symmetrical.

I thought you meant frequency for the time dimension but now
I think what you mean is how long does it take for the waveform to
become flat.

No. The flat part of the waveform is the low frequency component,
which is independent of the rise time. If the flat part sags, then
you are capacitor coupling (AC coupling) somewhere, probably the AC/DC
switch on the vertical input.

It looks like it takes .1 mS. And the overshoot is about
30mV

I can't tell if that means that it sags 0.1msec or the overshoot lasts
0.1msec. Perhaps a posting photo of the screen would be helpful.

More reading:
"The Secret World of Oscilloscope Probes"
<http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf>

The link in the video to EEVblog doesn't work. This does:
"EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed"
<http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Clifford Heath]

On 16/2/19 7:05 am, ggherold@gmail.com wrote:
> I never heard of form taps, but I'll look into them.

They make roll-forming screws also. Google "tri-lobe screw". They're
much better and more secure than self-tappers, and you can remove and
replace them multiple times without weakening the thread.

Clifford Heath.

 

[amdx]

On 2/15/2019 4:15 PM, Phil Allison wrote:

et...@whidbey.com wrote:



But with the probes set at 1x the square wave isn't quite square.
The 3 probes that have the 1x setting all act the same, with the
square wave being slightly distorted.

It didn't seem to matter if the 'scope was set to AC or DC
coupling. It also didn't matter if the signal being measured came from
the 'scope or from the function generator.



** Now that you have finally DESCRIBED the "distortion" ( a 10% overshoot) the answer is obvious.

The 465 scope is the culprit, the vertical attenuator needs frequency adjustment.

With the various probes in 10:1 setting, the trim cap allows you to compensate for the error in the scope.



.... Phil

Anyone wanting to store this list of TEKtronix probe characteristics
should do it now. The link is no longer functional, I went to the
Wayback Machine to locate it.

https://web.archive.org/web/20180104162744/http://www.reprise.com/host/tektronix/reference/voltage_probes.asp
It has info on about 100 different TEK probes.

Mikek

 

On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Fri, 15 Feb 2019 15:33:01 -0800, etpm@whidbey.com wrote:

Below is an answer I gave to Mike about the wave shape and other
features. The description should give you a better idea of what I am
seeing. At least I hope it does.

"Whoops! It looks like the wave is over compensated. So it looks like
at the beginning of the flat waveform it has a little peak that then
drops down to form a flat line for the rest of the wave.

Under compensated or too little capacitance. The overshoot of the
rising part of the square wave means you have too much high frequency
response.

This of
course repeats but in the negative direction for the negative part of
the wave.

Yep. If the negative going part of the waveform were not identical,
then your input square is not symmetrical.

I thought you meant frequency for the time dimension but now
I think what you mean is how long does it take for the waveform to
become flat.

No. The flat part of the waveform is the low frequency component,
which is independent of the rise time. If the flat part sags, then
you are capacitor coupling (AC coupling) somewhere, probably the AC/DC
switch on the vertical input.

It looks like it takes .1 mS. And the overshoot is about
30mV

I can't tell if that means that it sags 0.1msec or the overshoot lasts
0.1msec. Perhaps a posting photo of the screen would be helpful.

More reading:
"The Secret World of Oscilloscope Probes"
http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf

The link in the video to EEVblog doesn't work. This does:
"EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed"
http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all

Thanks again Jeff. I have watched EEVblog several times and haven't
had time yet to check out completely the episode mentioned. I looked
for it and just got it started when the dryer belt broke. Anyway, when
I spoke above about .1mS I meant that the overshoot lasts that long.
So there is a peak at the beginning of the square wave and then the
trace curves down to become flat. And the time it takes to become flat
is about .1 mS. The computer I am posting from is running XP and so I
can't use Dropbox. I should look for another easy to post to picture
site.
Eric

 

On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Fri, 15 Feb 2019 15:33:01 -0800, etpm@whidbey.com wrote:

Below is an answer I gave to Mike about the wave shape and other
features. The description should give you a better idea of what I am
seeing. At least I hope it does.

"Whoops! It looks like the wave is over compensated. So it looks like
at the beginning of the flat waveform it has a little peak that then
drops down to form a flat line for the rest of the wave.

Under compensated or too little capacitance. The overshoot of the
rising part of the square wave means you have too much high frequency
response.

This of
course repeats but in the negative direction for the negative part of
the wave.

Yep. If the negative going part of the waveform were not identical,
then your input square is not symmetrical.

I thought you meant frequency for the time dimension but now
I think what you mean is how long does it take for the waveform to
become flat.

No. The flat part of the waveform is the low frequency component,
which is independent of the rise time. If the flat part sags, then
you are capacitor coupling (AC coupling) somewhere, probably the AC/DC
switch on the vertical input.

It looks like it takes .1 mS. And the overshoot is about
30mV

I can't tell if that means that it sags 0.1msec or the overshoot lasts
0.1msec. Perhaps a posting photo of the screen would be helpful.

More reading:
"The Secret World of Oscilloscope Probes"
http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf

The link in the video to EEVblog doesn't work. This does:
"EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed"
http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all

Greetings Jeff,
Well, I watched that video you mentioned plus another two, one put out
by Tektronix. I now understand WAY better what's going on. Thanks for
the link and suggestions. I know it shouldn't matter but the EEVblog
guy's voice bugs me. But his explanation was clear. And the pdf you
posted a link to was also very educational.
Thanks,
Eric

 

[Jeff Liebermann]

On Tue, 26 Feb 2019 12:16:27 -0800, etpm@whidbey.com wrote:

On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann <jeffl@cruzio.com
wrote:
More reading:
"The Secret World of Oscilloscope Probes"
http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf

The link in the video to EEVblog doesn't work. This does:
"EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed"
http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all

Well, I watched that video you mentioned plus another two, one put out
by Tektronix. I now understand WAY better what's going on. Thanks for
the link and suggestions. I know it shouldn't matter but the EEVblog
guy's voice bugs me. But his explanation was clear. And the pdf you
posted a link to was also very educational.
Thanks,
Eric

Y'er welcome. There's also a mess of magic (and confusion) with high
voltage probes, where the frequency response varies with the applied
voltage. See graph on Pg 1-12:
<https://download.tek.com/manual/070822305.pdf>

Also active probes that work at GHz frequencies with input loading
around 1M and 1pf. You can really get spoiled with those working
around RF.
"Active probes: why they are worth buying"
<https://www.eetimes.com/document.asp?doc_id=1279659#>

I have the same problem with Dave Jones of EEVblog. Recently, he's
made an attempt to shorten his videos and clean up his presentation,
but it's still difficult viewing. Here's a clue:
<https://www.youtube.com/user/EEVblog>
"No Script, No Fear, All Opinions"
Methinks a script and an editor might help.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Mike]

On 2/26/2019 1:29 PM, Jeff Liebermann wrote:

On Tue, 26 Feb 2019 12:16:27 -0800, etpm@whidbey.com wrote:

On Fri, 15 Feb 2019 19:02:44 -0800, Jeff Liebermann <jeffl@cruzio.com
wrote:
More reading:
"The Secret World of Oscilloscope Probes"
http://www.dfad.com.au/links/THE%20SECRET%20WORLD%20OF%20PROBES%20OCt09.pdf

The link in the video to EEVblog doesn't work. This does:
"EEVblog #453 - Mysteries of x1 Oscilloscope Probes Revealed"
http://www.eevblog.com/forum/blog/eevblog-453-mysteries-of-x1-oscilloscope-probes-revealed/?all

Well, I watched that video you mentioned plus another two, one put out
by Tektronix. I now understand WAY better what's going on. Thanks for
the link and suggestions. I know it shouldn't matter but the EEVblog
guy's voice bugs me. But his explanation was clear. And the pdf you
posted a link to was also very educational.
Thanks,
Eric

Y'er welcome. There's also a mess of magic (and confusion) with high
voltage probes, where the frequency response varies with the applied
voltage. See graph on Pg 1-12:
https://download.tek.com/manual/070822305.pdf

That has nothing to do with the frequency response.
Probes are VOLTAGE derated with frequency.
Think about it...
At infinite frequency, all the caps look like shorts and
it lets the smoke out.

Also active probes that work at GHz frequencies with input loading
around 1M and 1pf. You can really get spoiled with those working
around RF.
"Active probes: why they are worth buying"
https://www.eetimes.com/document.asp?doc_id=1279659#

I have the same problem with Dave Jones of EEVblog. Recently, he's
made an attempt to shorten his videos and clean up his presentation,
but it's still difficult viewing. Here's a clue:
https://www.youtube.com/user/EEVblog
"No Script, No Fear, All Opinions"
Methinks a script and an editor might help.