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Let’s Talk About LeCroy Scopes, AKA… the “Wuerstchenhund Holds Court” Thread

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JPortici:

--- Quote from: Wuerstchenhund on September 14, 2016, 08:05:26 am ---Who's Mr K?

--- End quote ---

daniel, keysight.
a couple of months ago or so i saw new test equipment with black enclosures on keysight homepage, i remember it was mentioned even here at that time as a joke on them trying to look like  lecroy

https://www.eevblog.com/forum/testgear/opinion-keysight-new-design-theme/msg938112/#msg938112

don't need to take me seriously on that one :)

yes, what you say about loaner is true and what i fear is that they wouldn't care about loaning to privates, which is understandable to some degree.
it is also very stupid, on some degree. I already said i was a salesperson once and the worst thing you can do is to refuse the hint of a sale

Wuerstchenhund:

--- Quote from: JPortici on September 14, 2016, 10:32:14 am ---
--- Quote from: Wuerstchenhund on September 14, 2016, 08:05:26 am ---Who's Mr K?

--- End quote ---

daniel, keysight.
--- End quote ---

Ah, I see ;)


--- Quote ---a couple of months ago or so i saw new test equipment with black enclosures on keysight homepage, i remember it was mentioned even here at that time as a joke on them trying to look like  lecroy
--- End quote ---

Yes, I remember. KS's new signal analyzers are in black, which is somewhat interesting.

It seems however scope will stay beige/white


--- Quote ---yes, what you say about loaner is true and what i fear is that they wouldn't care about loaning to privates, which is understandable to some degree.
it is also very stupid, on some degree. I already said i was a salesperson once and the worst thing you can do is to refuse the hint of a sale

--- End quote ---

As I said it's only the occasional sales drone, most of them are happy to sell you a scope, or giving you a loaner.

David Hess:

--- Quote from: Wuerstchenhund on September 14, 2016, 07:43:35 am ---
--- Quote from: tautech on September 14, 2016, 12:44:19 am ---I too find it very odd that a WS3000 does not have Peak Detect.  :scared:
One can only imagine that it's been left out of the incorporated features on purpose, if indeed it is missing.
--- End quote ---

It is on purpose. PD was a crutch to overcome the very small sample memories of older digital scopes, allowing to sample at full sample rate for an extended amount of time by storing only the minima and maxima of a sampled group and thereby extending the time length that can be acquired. As it is an acquisition mode, it is destructive (i.e. you lose the original sample data). You also lose timing information (you know in which sample period the data points were acquired, but you don't know where in that period, i.e. at the beginning or the end).

...

I know that some people will probably disagree (I remember some discussions with nctnico about PD), but despite using mostly Keysight scopes at work which all have PD, I can't remember when the last time was when I used it (I vaguely remember one time in the early 2000's with some Tek scope). That of course doesn't mean much, and I'd be interested to hear about specific scenarios where people believe PD is still required - bearing in mind we're talking about a mid-range scope here, not some simple $400 Rigol box.


--- End quote ---

The connection between record length and peak detection reminds me of a recent post on the forum about the Rigol 1000Z linking record length and delayed sweep/acquisition.

The user in question was operating at a slow time/div but needed to magnify waveform details to such an extent at a point after the trigger point that the limited sample rate even with the Rigol's relatively long record length became a problem.  The question was whether the delay function could be used to acquire a full sample rate acquisition at the point of interest and I guess the answer was no; the Rigol's delay function *only* affects what is shown on the display and has nothing to do with the acquisition process despite what Rigol's documentation implies.  I managed to resist my inclination to respond that a gimpy Tektronix DSO with a 4K record length would have had no problem with this.

So both peak detection and delayed sweep/acquisition are crutches to overcome the limitations of a short record length.  I would also add DPO functionality to this list of crutches and I would rather have all three than a long record length if it means a faster update rate with lower blind time.


--- Quote ---These days, scopes come with reasonably large sample memories, which means even in normal mode you can run the scope at full sample rate for longer timbases. Also, modern scopes tend to come with a much larger sample rate to BW ratio (the 750Mhz WS3074 samples at 4GSa/s, the 1Ghz DSOX3104T at 5GSa/s), which means there is lots of room for the sample rate to drop without losing any details. With its 10Mpts memory, even the 750MHz WS3 can aquire a 5ms period at sufficient sample rate (2GSa/s). And the lower the analog bandwidth the further the sample rate can be dropped without losing detail.
--- End quote ---

I am not sure if this is what you meant to say.  That modern DSOs typically come with a large maximum sample rate to bandwidth ratios makes no difference when the sample rate is limited by record length unless they have peak detection, delayed sweep/acquisition, or something similar going on between the digitizer and acquisition record.

Wuerstchenhund:

--- Quote from: David Hess on September 14, 2016, 12:15:12 pm ---The connection between record length and peak detection reminds me of a recent post on the forum about the Rigol 1000Z linking record length and delayed sweep/acquisition.

The user in question was operating at a slow time/div but needed to magnify waveform details to such an extent at a point after the trigger point that the limited sample rate even with the Rigol's relatively long record length became a problem.  The question was whether the delay function could be used to acquire a full sample rate acquisition at the point of interest and I guess the answer was no; the Rigol's delay function *only* affects what is shown on the display and has nothing to do with the acquisition process despite what Rigol's documentation implies.  I managed to resist my inclination to respond that a gimpy Tektronix DSO with a 4K record length would have had no problem with this.
--- End quote ---

Well, that is not surprising, considering that the Rigol DS1000z is a $400 scope with very limited functionality. I already said that for low end scopes PD is sometimes the only option. But we're not talking low-end scopes here.


--- Quote ---So both peak detection and delayed sweep/acquisition are crutches to overcome the limitations of a short record length.
--- End quote ---

In essence, yes. PD may have some place in a low end scopes with limited trigger/analysis capabilities but again, this isn't what we're talking here.


--- Quote ---I would also add DPO functionality to this list of crutches
--- End quote ---

Yes, it's a crutch, because Tektronix was simply unable to produce an architecture that delivers fast update rates in normal mode. DPO mode has several disadvantages, like no measurements, because like other acquisition modes its destructive (i.e. the original sampling data is gone).

DPO is one of many reason why pretty much no-one in its right mind buys Tektronix scopes these days, aside maybe from teh edu sector which now seems to be Teks main customers and which is full of people that live in their own world.


--- Quote ---and I would rather have all three than a long record length if it means a faster update rate with lower blind time.
--- End quote ---

Great. But this tells me that you somehow missed the whole point I was making, which is that the lack of PD on the WS3000 is made up by other tools. Don't take this the wrong way but you sound like the type of person that if sat in front of a modern high end scope and asked to find and measure a glitch would resent to persistence mode and cursor readouts.

There's a reason why a modern mid-range or high-end scope has advanced toolsets, which is that you don't have to rely on crutches that pretty much only exist because of limitations in test gear 20 years ago.



--- Quote ---
--- Quote ---These days, scopes come with reasonably large sample memories, which means even in normal mode you can run the scope at full sample rate for longer timbases. Also, modern scopes tend to come with a much larger sample rate to BW ratio (the 750Mhz WS3074 samples at 4GSa/s, the 1Ghz DSOX3104T at 5GSa/s), which means there is lots of room for the sample rate to drop without losing any details. With its 10Mpts memory, even the 750MHz WS3 can aquire a 5ms period at sufficient sample rate (2GSa/s). And the lower the analog bandwidth the further the sample rate can be dropped without losing detail.
--- End quote ---

I am not sure if this is what you meant to say.  That modern DSOs typically come with a large maximum sample rate to bandwidth ratios makes no difference when the sample rate is limited by record length unless they have peak detection, delayed sweep/acquisition, or something similar going on between the digitizer and acquisition record.
--- End quote ---

The point is that back then in 1996 a standard 100Mhz DSO like the HP 54622A came with 200MSa/s sample rate, while a modern day equivalent samples at 2Ghz or more. The large oversample ratio on modern scopes means it doesn't necessarily have to run at full sample rate to get all the details, meaning on a scope that lets you manually select the sample rate you can simply drop the sample rate to extend the acquisition period even more.

nctnico:

--- Quote from: Wuerstchenhund on September 14, 2016, 10:13:21 am ---
--- Quote from: nctnico on September 14, 2016, 09:44:36 am ---Even with long memory I use peak detect often at low sweep rates to make sure I don't miss a narrow pulse c.q. see a trace which has all the expected elements and nothing missing or malformed due to aliasing. It is true that timing information is lost but when looking at (for example) video signals it is nice to see the hsync and vsync pulses are all there. To me having no peak detect is a show stopper.

--- End quote ---
I understand. Well, on a LeCroy scope I would rather use WaveScan for that.

Your scenario is actually not too unsimilar to a pet project of mine, where one element relies on a set of (unevenly spaced) sync pulses. To find out if pulses are missing or out of spec I just throw WaveScan at it and let it run for a while, it then tells me any pulses were missing/out of spec, and if so presents me with a nice histogram showing when exactly that happened. If I wanted I could even set it up to do specific measurements on malformed pulses, or just let it do some screen shots everytime a deviation occurs, or do a range of other stuff.caused it.

Granted, on a entry-level scope which doesn't have any advanced functionality, PD is probably the best (only?) way to do that.

--- End quote ---
You are missing my point slightly. For a first cursory look at a signal I'd like to see it's extremes at all timebase settings (even the slowest ones and roll mode) and for that peak detect is the only option. Sometimes I have to look at signals from systems which are slow but can have glitches. Even worse: I have no idea what to expect. So I set the scope to roll mode with peak detect on to get a feel for what a signal does (amplitude and if there are pulses at all) over a period of seconds to minutes. From there I can switch to triggering on glitches etc.

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