Questions for owners of Agilent X-Series oscilloscopes

[Franki]

hi everyone

 I have several question about some features of the Agilent X-Series oscilloscopes I'm considering before buying some for me and my friends:

1.)
a) does it support live transferring of the acquisitioned data over the LAN/VGA or GPIB? (for long-time automated live transferring of measurements, evaluations and then regulations; "automated live transferring" meaning it sends out data without anyone interacting with the scope while the measurement is still going on)?
b) If not fully, does it do that at least for lower sample rates? The acquisition/transferring delay need not be that low, several seconds delay would be low enough.

2.) what is the slowest possible data acquisition rate in terms of sample rate(for long term monitoring)? 1 sample every 1, 2 or 5 seconds? The specs says the maximum time base range is 50s/div , but then, how many samples does it have per division?

3.) does it have a floating ground switch/mode? Can its ground on the input line be disconnected from protective earth? Or should one rather use a differential probe, even for measurements <100kHz?

I hope some owners of these scopes, and I hope for Dave, can help me.

THX for the info in advance

[EEVblog]

1) Not sure, you'd have to actually try. More than likely, and you might want to consider using the ROLL mode.

2) Yes, it's 50s/div. Do the math based on the memory size for samples/div.

3) No. No scope I know of has this. Only scopes specifically designed with floating inputs.

Can you get a demo unit from your local rep?

Dave.

[Franki]

1) Not sure, you'd have to actually try. More than likely, and you might want to consider using the ROLL mode.

Trying is good, when you have the money or if the vendor accepts returned devices. BTW, that's something I should check.

If you can't or won't check that on your devices or someone else here can't or won't do it, I would have to write another email to the vendor.

2) Yes, it's 50s/div. Do the math based on the memory size for samples/div.

I just don't see how to infer from the memory size and other data from the specs what the samples/div is, or am I confused?

3) No. No scope I know of has this. Only scopes specifically designed with floating inputs.

One of my friend says he knows some old Philips and Tektronix scopes that had this.

Can you get a demo unit from your local rep?

they don't have demo units, they only order some on specific orders from their customers and they need full payment in advance And this is the only retailer in my state (AFAIK) that sells these devices to private persons so this is why I need to ask all those questions before buying them

THX

[alm]

1.)
a) does it support live transferring of the acquisitioned data over the LAN/VGA or GPIB? (for long-time automated live transferring of measurements, evaluations and then regulations; "automated live transferring" meaning it sends out data without anyone interacting with the scope while the measurement is still going on)?
b) If not fully, does it do that at least for lower sample rates? The acquisition/transferring delay need not be that low, several seconds delay would be low enough.

You can sample the full memory in one go, and transfer the results to a computer (at least any DSO with SCPI support I've seen does). Scopes are not usually designed as digitizers, so I doubt you can do this continuously (but if the transfer delay is acceptable, it might work). Transferring the full memory is likely to take more than a few seconds.

I'm not sure if the standard software supports acquiring data in a loop, you may have to do some programming or buy something like SignalExpress for that.

I just don't see how to infer from the memory size and other data from the specs what the samples/div is, or am I confused?

Samples/div = record length / number of horizontal divs? This usually falls apart at the very fast sweep speeds, since the scope typically doesn't have enough sample rate for that.

3) No. No scope I know of has this. Only scopes specifically designed with floating inputs.

One of my friend says he knows some old Philips and Tektronix scopes that had this.

I've seen at least one ex-Tektronix employee deny that Tektronix ever installed such a thing. Was probably a custom mod by the customer. There are easier ways to get fried without having to buy a $1k+ scope.

[mikeselectricstuff]

1.)
a) does it support live transferring of the acquisitioned data over the LAN/VGA or GPIB? (for long-time automated live transferring of measurements, evaluations and then regulations; "automated live transferring" meaning it sends out data without anyone interacting with the scope while the measurement is still going on)?
b) If not fully, does it do that at least for lower sample rates? The acquisition/transferring delay need not be that low, several seconds delay would be low enough.

You can sample the full memory in one go, and transfer the results to a computer (at least any DSO with SCPI support I've seen does). Scopes are not usually designed as digitizers, so I doubt you can do this continuously (but if the transfer delay is acceptable, it might work). Transferring the full memory is likely to take more than a few seconds.

I'd suggest reading the programming manual which is on the Agilent site

3) No. No scope I know of has this. Only scopes specifically designed with floating inputs.

One of my friend says he knows some old Philips and Tektronix scopes that had this.

I've seen at least one ex-Tektronix employee deny that Tektronix ever installed such a thing. Was probably a custom mod by the customer. There are easier ways to get fried without having to buy a $1k+ scope.

There are some Teks with isolated inputs. My guess is for safety reasons they may not have an option to ground them, although it would be useful.

Have any DSOX's actually made it to customers yet? I've not seen any evidence of stock showing at distributors like RS or Farnell

[alm]

There are some Teks with isolated inputs. My guess is for safety reasons they may not have an option to ground them, although it would be useful.

I believe even the TPS2000 series is grounded when using the AC adapter, only the inputs are isolated. Although it doesn't need a ground connection in battery powered mode, unlike almost all other bench scopes. Since the inputs are floating, you are free to connect the reference voltage to any potential (within rated voltage) you like, including PE. No need to have a switch in your scope for that.

[mikeselectricstuff]

If I had a scope with isolated inputs I really would want a switch to optionally ground them, probably with a very obvious indication that it was enabled.
When doing non-critical probing on something that is grounded (e.g. PC connected) , you can often get away with not using the probe ground, which saves some time & fiddling if there isn't an easily clippable ground point.

When I use a battery powered scope, having to always find a ground can be rather annoying.
 

[Psi]

Maybe you could have a look around for companies that hire out test equipment.

It might be relatively cheap to hire one for a day and check if it does what you want.

[Franki]

Since the inputs are floating, you are free to connect the reference voltage to any potential (within rated voltage) you like, including PE. No need to have a switch in your scope for that.

This is actually what I need, a decent scope with floating inputs, that optionally allows for one input to be connected to ground. I would have no problem with a properly earthed metal shielding around the scope circuitry but insulated from the inputs and the scope circuitry. This would also imply that the entire scope circuitry starting from the secondary side of the insulating mains transformer be insulated from earth.

I don't know why there aren't more scopes of that kind. Maybe because this renders HF measurements more difficult.

It's said that the clean way to measure differetials is to use a differential probe.
But I just recently saw an offer for the regular differential probe for the Agilent InfiniiVision 2000 X-series that was priced at about 1376€. Jee! that's more expensive than the entire scope!! And when one reads the spec of that probe, it read:

The N2792A 200 MHz and N2793A 800 MHz differential probes provide the superior high-speed differential signal probing required by today’s high-speed power measurements, automotive bus measurements, and high-speed digital system designs.

I neither need the scope to do 800MHz high-speed nor high power measurements. So this would be a complete waste of money. Ahhh!

On the other hand, one may use 2-inputs with ground unplugged and switching to A - B mode, but that wastes one precious little input chanel. And besides, I doubt the sample quality in this mode of operation would be as good as using a true floating inputs scope for my purposes.

I got the impression that for measuring non-HF differential AC signals, a film cap each between the ground and input of the scope and the ground and output of the test circuit or a similarly well suited air coiled line transformer would do the job perfectly.

But what shall one do when the AC signal has a DC offset? Always disconnect this galvanic isolation and do a second DC measurement?

Or is there a reasonable feasable way to transform a regular Agilent scope into a floating input scope without sacrificing the security of a protective earth shielded chassis and without completely compromising the EMI characteristics? I guess one would need at least a new pair of input sockets (2 signals+GND instead of 1 signal+GND each) and a new pair of probes(2 twisted signal lines shielded by GND instead of just 1 signal line shielded by GND each). Would that be more economic than buying an overfeatured and overprized differential probe?

[Franki]

When I use a battery powered scope, having to always find a ground can be rather annoying.

Yes, but always having the wrong ground is even more annoying, especially when you are not only dealing with measurements on power lines or digital paths.

[alm]

I don't know why there aren't more scopes of that kind. Maybe because this renders HF measurements more difficult.

It's definitely much more complex, even for the relatively low-spec TPS2xxx series (I think max BW is only 200MHz). They also produce more noise because of the isolation circuit. The Fluke ScopeMeters are also in that category by the way, but as far as I know, very few other manufacturers. Not sure why Agilent or Lecroy don't have one.

It's said that the clean way to measure differetials is to use a differential probe.
But I just recently saw an offer for the regular differential probe for the Agilent InfiniiVision 2000 X-series that was priced at about 1376€. Jee! that's more expensive than the entire scope!!

Yes, probes are expensive. Note that even a good, brand-name passive probe will easily exceed $100, sometimes even $300, it's not just a piece of cable. Active probes are obviously even more complex. If you don't need high bandwidth or high CMRR, I believe there are some cheaper differential probes (eg. by Testec and Picotech) with bandwidth up to 100MHz for something like $300-$500. They will obviously need an external power supply, since the probe power interface tends to be proprietary. No experience them, I expect them to be OK, although common mode rejection ratio (CMRR) at high(ish) frequencies or voltages (voltage coefficient) will probably be inferior to the expensive brands because of a cheaper attenuator design, since good CMRR requires very careful matching of the attenuator components between channels.

On the other hand, one may use 2-inputs with ground unplugged and switching to A - B mode, but that wastes one precious little input chanel. And besides, I doubt the sample quality in this mode of operation would be as good as using a true floating inputs scope for my purposes.

CMRR will be horrible, probably only 20:1 or 50:1, even at low frequencies, as opposed to 1000:1 and better for a good diff probe. How important this is depends on your common mode signal. Don't be surprised to see a 50/60Hz sine superimposed on your signal.

Or is there a reasonable feasable way to transform a regular Agilent scope into a floating input scope without sacrificing the security of a protective earth shielded chassis and without completely compromising the EMI characteristics?

Not without spending a lot of money or time. An isolation amplifier might work (Tek made one at some point), but is not exactly cheap or simple.

I guess one would need at least a new pair of input sockets (2 signals+GND instead of 1 signal+GND each) and a new pair of probes(2 twisted signal lines shielded by GND instead of just 1 signal line shielded by GND each). Would that be more economic than buying an overfeatured and overprized differential probe?

What's the point of this? What would you connect the two signals to, the input circuitry is only single-ended. There were some scopes with differential inputs (the Tek 7000/11000 series with the correct plugins, for example), but that's fairly rare. I guess you could build your own differential probe if you don't require high bandwidth or high voltage. There is at least one design (by Elektor?) around. They usually use something like a differential video line driver as active stage, and some sort of attenuation before this. This is basically what commercial probes are doing. I wouldn't expect great bandwidth or CMRR from a DIY design, though.

[Franki]

On the other hand, one may use 2-inputs with ground unplugged and switching to A - B mode, but that wastes one precious little input chanel. And besides, I doubt the sample quality in this mode of operation would be as good as using a true floating inputs scope for my purposes.

CMRR will be horrible, probably only 20:1 or 50:1, even at low frequencies, as opposed to 1000:1 and better for a good diff probe. How important this is depends on your common mode signal. Don't be surprised to see a 50/60Hz sine superimposed on your signal.

I don't care so much for the CMRR, but the mains frequency sine superimposed on the signal really sounds like the same problem I have with my 20MHz analog HAMEG scope in the same measuring setup, and it really sucks.

I guess one would need at least a new pair of input sockets (2 signals+GND instead of 1 signal+GND each) and a new pair of probes(2 twisted signal lines shielded by GND instead of just 1 signal line shielded by GND each). Would that be more economic than buying an overfeatured and overprized differential probe?

What's the point of this? What would you connect the two signals to, the input circuitry is only single-ended. There were some scopes with differential inputs (the Tek 7000/11000 series with the correct plugins, for example), but that's fairly rare. I guess you could build your own differential probe if you don't require high bandwidth or high voltage. There is at least one design (by Elektor?) around. They usually use something like a differential video line driver as active stage, and some sort of attenuation before this. This is basically what commercial probes are doing. I wouldn't expect great bandwidth or CMRR from a DIY design, though.

The new pair of sockets and probes are meant to come along with some modification of the scope's internal circuitry, namely to isolate the secondary side(s) of the power transformer(s) of the scope and all of its associated circuitry and the inputs from earth(including what previousy were the GND inputs and paths), while keeping the metal chassis of the scope grounded to earth. Then, the now floating GND inputs become a secondary input line for each channel, just as it is the case with a differential probe. And to keep these 2 input lines shielded, one would have to add an shielding line around them, that is either connected to the earth chassis from the scope or to the earth from the test circuit. So this gives you know:
=  1 input line
=  1 GND line(isolated from earth)
=  1 earth line
per input channel.

Of course, the scope needs a real isolation transformer on the power line for this to work.

The other option would be to use an isolation transformer / film caps on the input line, at least for AC only.

[Franki]

I just don't see how to infer from the memory size and other data from the specs what the samples/div is, or am I confused?

Samples/div = record length / number of horizontal divs? This usually falls apart at the very fast sweep speeds, since the scope typically doesn't have enough sample rate for that.

From what I can see from the data sheet, the X-Series 2000 has a record length of 100k samples and 10 horizontal divs. According to your formula, this would give 10k samples/div. I'm looking for the minimum samples/div it can do, and that's not possible. Are you sure we are talking about the same horizontal divs?

My approach to calculate the samples/div was to take the horizontal screen resolution and divide it by the number of horizontal divs, which would yield 800/10= 80 samples/div. Of course, that only works if you have exactly 1 sample per pixel, and I doubt that this is the case for the slowest sampling speed.

[EEVblog]

The scope will always use it's full 100K memory at all sample rates, that's how digital scopes work.
Why do you want to limit it to less?

Dave.

[Franki]

The scope will always use it's full 100K memory at all sample rates, that's how digital scopes work.

of course

Why do you want to limit it to less?

Well, I don't want to limit the amount of memory it uses for aquiring samples. What I want to do is ask for a friend how low the sample acquisition rate of the Agilent scopes for long-time measurements (possibly over a day) can get. For that purpose, it would be good if the Agilent scopes had acquisition rates of at most 1Sa/s. I think the time bases the most interesting for that purpose would be the 10Sa/div to 50Sa/div.

My friend tried to use a DMM for that, but that didn't work for some reason.

[EEVblog]

As already stated, the lowest time/div setting is 50S/div, and it says that gives 100samples/s
No point having the samples any slower, because with the big memory those samples come for free.

Dave.

[mikeselectricstuff]

Bear in mind the number of samples is reduced in peak detect mode (/4) and normal/auto modes (/2). And if digital channels are enabled.