Floating the 'scope

Sufficient offset range achieves the same measurement result.

I see no advantage to being able to measure it at a front panel socket compared to having the scope tell you what the offset voltage is.

You mentioned "calibrated comparison voltage" and "measuring staircase steps". The calibrated deflection factor serves the function just as well.

Hardly the same as having four color traces on one screen, is it?

Indeed. So since I had already told you that the TPS2024 had 4 effectively differential inputs, why did you mention "You can put amplifiers in timebase slots. Full differential X-Y." as though that were an advantage that the 7A13 has that the TPS2024 doesn't?

This whole back and forth seems to consist of you telling me things that the 7A13 can do that the TPS2024 can't. So for, I see that the TPS2024 substantially outshines the 7A13. Others can draw their own conclusions.

A 7A13 is wonderful in lots of apps, but it won't do differential input and offset at the same time.

If I have, say, a power amp with +-200 volt rails, and I want to measure the waveform across a small-value resistor flailing around with the output voltage, the TPS is perfect. And the traces are in color!

John

Just one point, then, The 7A13 will measure a 1mV portion of a 10V signal. That's nearly four times the 8 bits resolution, which I believe the TPS2024 has.

Two 7A13s, mainframe set to add, channel 1 Vc to -ve, channel 2 Vc to +ve.

Never done it, but I'll try when I get a chance. CMRR won't be as good, admittedly.

Never could get along with digital 'scopes. Only use one when I want to save or print a trace.

I find different-colored traces confusing. I see colors as numbers. Can you color the traces in number order - R, Or, Y, G, etc? That might work for me.

piece of

ground

ed.

Thanks Michael, The isolation transformer is on order.

George H.

=A0 =A0 =A0 =A0 =A0(Stephen Leacock)

Digital scopes use to have terrible user interfaces. But they are so much better now. The colored knobs are associated with the trace color. It's so easy to know which knob to grab... try it you may like it.

George H.

That's like using two probes in A-B mode. The equivalentcommon-mode rrange is small, because the internal amps saturate at the equivalent of a couple of screens worth of offset. The TPS can show tou a 10 millivolt signal riding on the AC line, with 200 MHz bandwidth.

The 7A13 is great for huge amounts of zooming, like looking at pulse tops or recovery to zero. It recovers from massive overloads instantly, which most scopes don't do very well.

Nowadays I find all-green scopes confusing. And I know that the purple probe is the purple trace. Nice.

John

Yeah, some of the early digital scopes, especially the HPs, were nightmares to drive. It turns out that the classic arrangement of knobs is best, so most digital scopes now resemble old analog scopes.

John

Good deal! Just don't get careless when using it. :)

If I can find one with better than 500Mhz effective bandwidth, 12 bit or better resolution and no Windows interface, I'll probably buy one.

Had a rep a while ago trying to sell me one of Tek's offerings. Switched it on, up came "My Oscilloscope" or some other Windows "My Little Pony" crap. Switched it off and sent him packing.

They'll be painting them pink, next :-)

Pretty much what I said.

With only 8 bit resolution?

Which is precisely what I need.

Purple isn't a color that shows up well to me. Those "actinic blue" fast phosphors that Tek used to offer as an option were absolute torture. Instant blinding headache.

That should be trace #7, anyway ;=)

Never buy any instrument that has Windows inside!

The only analog scope I still use is our 7104, 1 GHz microchannel thing. Equivalent digital scopes are way too expensive.

The 11801-series of samplers go to 40 GHz and are cheap nowadays.

John

Signal averaging is magic. Hey, this is 2010!

John

I never intend to. Hell, I won't buy a PC that has Windows inside !

Got one of those, too.

I've been thinking about one of those.

I'd still be happier with 12 bits, but then I just don't like digital. I always feel like I wanna see between the samples ;-)

worked.

any

Yeah well Phil A. hasn't answered, but it seems that even with the scope plugged into an isolation transformer, you can still get 'whacked' if you attach the probe 'ground' to the wrong spot.

George H.

much

=A0 It's

=A0 =A0 =A0 =A0 =A0(Stephen Leacock)

Yeah there is the windows thing. I don't know what you can do about that. If you are not looking at transient behavior (one shot sort of stuff.) then the signal averaging on the digital scope is a real bonus. I used an HP infinium scope at the FEL in Vanderbilt. I think it did 500MHz, but when you turned it on up popped the windows icon... ugh, you had to wait while the operating system booted.

"Yeah well Phil A. hasn't answered, but it seems that even with the scope plugged into an isolation transformer, you can still get 'whacked' if you attach the probe 'ground' to the wrong spot."

You can get whacked if you don't follow the one-hand-in-pocket rule, but otherwise you're fairly safe. However, some isolation trannies have fairly large capacitance across the isolation barrier, and you could get a nasty tingle that might startle you and cause you to self-inflict injury. A medical grade tranny is the best, but you're looking at big bucks unless you get a good surplus deal.

It may also be prudent to use a GFCI circuit. It is cheaper and smaller than a transformer and will protect against an inadvertant conduction of line voltage to ground through the user's body. But if you use both hands and make a normal mode connection across the line voltage through your body, you might be toast. Or more likely get a case of V-fib. 60 Hurts Per Second is just about the most dangerous frequency.

Paul

Way back in 1989 I decided to buy a DSO, and I had been working at a company that was a distributor for Tektronix, so I was able to evaluate one of their scopes and I could have gotten it at cost. But I found the interface very confusing and frustrating. In general, I liked HP's panel layout better than Tek's. But I think the HP DSOs were too pricey for my budget. I ended up purchasing a Hitachi VC-6025, for something like $2000, and it is still working perfectly. It meets all my needs and I find the user interface simple and comprehensive.

At that time I also had used a LeCroy digital scope, which was nice, but hugely expensive. And I also used a Data Precision waveform analyzer, which was also very expensive, but we needed the high accuracy and the math functions such as true RMS of portions of the waveform between cursors.

We didn't need high frequency response, as we were measuring mains AC voltages and currents at 60 Hz. But we were developing instrumentation rated at 1% accuracy, so we needed 0.25% or better for our standard.

Prior to the DSOs and waveform analyzers, back in 1975-1979 when I was first working on this class of instrumentation, we bought a Visicorder from Government Surplus to observe the waveforms of the current pulses we needed to analyze. That was fun, loading up rolls of photosensitive paper, and timing the start of the recorder with the test set, and then going through the pile of paper and trying to make accurate guesstimates of RMS value and time. Ah, the good old days...

Paul