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Differential probes

Hi:

I have a Tek P5205 1:50/1:500 100MHz probe. I just tested it with a

1MHz square wave and it gives nice clean edges with little ringing.

However, a Fluke DP120 20MHz 1:20/1:200 probe loaned to me by an Agilent sales rep. gives miserably ringing edges. The Fluke is kind of silly in having 4 ft. long heavy cables with huge probes that look suitable for heavy duty power distribution probing. Not very convenient for little stuff.

But worse, the Fluke gives horribly ringing edges. I tried making the test cables into a twist-pair, which helped a little but not much. Do the designers ever really think that the thing can give meaningful measurements of 20MHz signals with such a huge pickup loop area! Also, the FP120 is about 4x more noisy than the Tek. The Fluke must have a power supply in there to generate a negative supply, whereas the Tek just pulls clean power from the scope.

Ugh!

The problem with the Tek is it can only work with the scope. But I need to look at a filtered signal to get better RMS measurements of PWM BLDC motor terminal voltages.

Although the FLuke gave a little better 1MHz CMRR of about -66dB vs. Tek

-49dB.

There are also a bunch of probes on the market that look like this:

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I wonder how they perform?

Oh well, just deliberating in public.

Thanks for input.

--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
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Reply to
Chris Carlen
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Chris Carlen wrote in news: snipped-for-privacy@news3.newsguy.com:

TEk used to make a separate power supply for the newer powered probes,an

1106 or something similar.It had two BNCs with the probe power terminals around the BNCs. 
--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

Hi Chris,

Tek make the P5200, its essentially the same thing as the 5205 sans scope power. 50R output Z too, whichis kinda handy. I made a bunch of

8th order 50R Bessel LPFs so I can directly measure PWM messes with them.

there is also a crowd who make the best damn diff probe there is. Alas I forget their name, they are a bunch of ex-tek engineers. Maybe Jim Yanik will tell us. not cheap though.

your comments wrt loop area are spot on.

Cheers Terry

Reply to
Terry Given

Tektronix 1103, actually. A fine piece of equipment, although realistically what you're buying is some trivial electronics but the proper Tektronix connectors; there was a VERY hefty margin on it!

There was also a very small, single probe version -- about 2"x1"x1", meant to plug "in-line" with a 'scope, with an external power supply -- but it never saw the retail light of day. A lot of prototypes were made of it (and shipped out to customer for beta testing), though, so once in awhile someone on eBay might sell one.

---Joel Kolstad

Reply to
Joel Kolstad

We just got a new Tek TPS2024 scope. It's a 4-channel, 200 MHz color scope and all four channels plus the trigger inputs are isolated. So you can use regular 1:1 or 10:1 probes for off-ground measurements at millivolt sensitivity. Slick.

The 50:1 attenuation of the P5205 turns low-level stuff to mush.

John

Reply to
John Larkin

Yeah, another thing I'd like is something with less attenuation.

Those isolated input scopes are really nice. Too bad they didn't put in at least a bit more sample memory. The TDS3000 series is really looking pale compared to Agilent's 6000 series. But both now have lower priced scopes. They seem to be not bothering to compete at the low end with record depth, but just color, screen res., and speed. Not that those aren't yummy on their own! It's really awesome what's available compared to a decade ago.

I just hope something like the MSO6014A will be about half the price in about 5 years.

John, why didn't Tek publish CMRR figures for that scope? Have you done any tests?

Good day!

--
_____________________
Christopher R. Carlen
crobc@bogus-remove-me.sbcglobal.net
SuSE 9.1 Linux 2.6.5
Reply to
CC

Yes, it's the 1103, which is insanely expensive. Maybe I'll get the standalone P5200. Don't know why they dropped the BW on that one though.

--
_____________________
Christopher R. Carlen
crobc@bogus-remove-me.sbcglobal.net
SuSE 9.1 Linux 2.6.5
Reply to
CC

Yeah, that's what I'll be doing.

I wonder if it's this "Preamble" company:

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???

But in a brief search, I couldn't find them. Or are they now part of LeCroy?

They're mentioned in some Linear app notes, 92, 86, and 85 for instance.

Good day!

--
_____________________
Christopher R. Carlen
crobc@bogus-remove-me.sbcglobal.net
SuSE 9.1 Linux 2.6.5
Reply to
CC

Terry Given wrote in news:1150762829.403566@ftpsrv1:

Don't know what you're referring to,if I did,I'd tell you.

There used to be a company that made a 3 slot "mainframe" for using 7000 series plug-ins,no display,only a single-ended 50 ohm output BNC. you could use that and either a 7A13(100Mhz) or 7A22(1Mhz) diff vertical amp.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

John Larkin wrote in news: snipped-for-privacy@4ax.com:

It won't have the CMRR of a true diff amp.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

CC wrote in news: snipped-for-privacy@news2.newsguy.com:

AFAIK,none of TEKs TDS scopes have CMRR comparable or anywhere near the old

7A13 or 7A22,or their standalone diff probes. They were never designed for good CMRR. 
--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

The TPS2024 is truly isolated to 600 volts RMS and goes down to 2 mv/cm, which is pretty extreme. It would be nice if it had the 10 uv/cm sensitivity and switchable bw of a 1A7A/7A22.

Maybe I'll make a little battery-powered preamp box to front-end the

2024 and get down to microvolt levels; switchable bandwidth would be handy, too. It could be single-ended, since the scope provides the isolation.

Does anybody make male BNC connectors with plastic (insulated) connector shells?

John

Reply to
John Larkin

John Larkin wrote in news: snipped-for-privacy@4ax.com:

So what? That has nothing to do with differential amp performance. All that means is the front ends are isolated from the case to 600 V.

The 7A13 has a wide input overdrive capability,has matched attentuators carefully calibrated for low CMRR,and a true low CMRR differential amplifier. AFAIK,NONE of the TDS series were designed to have true differential capability,just the simple "invert&add Ch2" sort like the older analog scopes.

Many of the TDS series have an adjustable BW-limit feature.

It still would make a lousy differential amp.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

I think I bought some chassis mountable, with round (or "D") hole rather than flange mount male BNCs from Pasternack. Not plastic, but you could stick heatshrink over it.

--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.
Reply to
Chris Carlen

On Mon, 19 Jun 2006 16:49:57 -0700, Chris Carlen wrote: ...

Forgive the stupid question, but doesn't it have a compensation adjust?

Thanks, Rich

Reply to
Rich Grise

Nope. I've yet to see an adjustment on any of these high-voltage active diff. probes.

--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.
Reply to
Chris Carlen

Chris Carlen wrote in news: snipped-for-privacy@news2.newsguy.com:

Mount the BNCs on a sheet of plastic,then mount the plastic to your box.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

Yeah, for chassis isolation, I was planning to use a bushing to insulate the hole, and fiber backing washer. A little easier than a plastic flange.

For John, the heatshrink idea was just to insulate the shell of the BNC plug.

--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.
Reply to
Chris Carlen

Then they are meant for 50 Ohms termination. Good Lord.

--
ciao Ban
Apricale, Italy
Reply to
Ban

That sure sounds differential to me. And it sure lets me measure stuff that nothing else can.

But it can't usefully look at signals on an opamp that's running 180 volts off ground, which is specifically why I bought the scope.

But clear down to 100 Hz would be nice. At 10 uV/div and 20 MHz bw, all I'd ever see would be radio stations.

I don't want to play with words, I want to measure things.

John

Reply to
John Larkin

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