Products > Test Equipment
Let’s Talk About LeCroy Scopes, AKA… the “Wuerstchenhund Holds Court” Thread
Wuerstchenhund:
--- Quote from: nctnico on September 14, 2016, 02:31:08 pm ---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.
--- End quote ---
I'm sorry and maybe I still miss your point but that sounds like a perfect scenario for WaveScan (which is *not* a trigger btw, it's more like a search tool/glitch finder, and it finds stuff that triggers won't). Instead of going through various time base settings I'd just enable WaveScan and let it search for deviations, and then just let it run for a while (5 seconds, 30s, a few minutes, ten days, whatever is appropriate). WaveScan will tell me exactly what went wrong at which point in time.
The problem with PD is that, while it can show small glitches on scopes that don't have enough memory to sustain a longer acquisition cycles at sufficient sample rates, it will show a somewhat malformed signal because of the loss of timing resolution. It also adds non-existing noise to the waveform, and overemphasizes infrequent amplitude deviations. It's OK for identifying glitches but pretty worthless to make a qualitative assessment of a signal. And PD won't show me anything that WaveScan can't find, without having me to stare at the screen to whole time waiting for an event to appear.
And while you used PD to find out that there are in fact glitches or dropouts in your signal and start to setup your triggers to catch them, WaveScan can already have done the work and provided me with screenshots of the glitches, or measurements.
One caveat though: WaveScan on the WaveSurfer Series is a simpler version of WaveScan on the high end scopes (WaveRunner, WavePro, WaveMaster, LabMaster) and lacks some of its capabilities. Not having a WS3000 myself (I only had one for a day) I can't exactly say what WaveScan on the WS3000 can and can't do. But I'm pretty sure, for your given scenario, it would easily find all dropouts and other problems with your signals.
nctnico:
Wavescan sounds like a perfect tool for letting the scope find 'errors' in a signal. However every now and then I find myself in a situation where I hook up a scope to a system and I have no idea what to expect so the first thing I want is a slow recording (seconds per divisions) of some signals which may be interesting. Roll-mode or long time/div with peak detect are really crucial because that way I have both an overview of what happens on a long timescale and an indication if there is or isn't something happening on shorter timespans. From your description I don't see how wavescan can do the same but then again I have never seen Wavescan in action.
AutomationGuy:
In WaveScan you can assign limits to any math function like rise time, peak width, duty cycle, RMS and so on ... on a trace and when the limits are -touched the trace will be stored. I am sure you can find any peak with WaveScan.
That way you can leave your scope running for days and review the stored anomalies next day. The high end scopes probably have much more math functions.
Actualy I could find signals using LeCroy scopes in some cases where I couldn't find them using other scopes.
Here are some feature requests in case someone from LeCroy is reading this:
I would like to have WaveScan on FFT which would include math functions on a FFT trace.
Another nice feature on the WS3000 would be a SENT decoder.
A Hex number comparison trigger on the MSO would be nice as well. (Could be availble already. I was missing it in an earlier SW version)
One thing about the WS3000 which annoys me is the autosetup which probbaly breaks sampling for a few seconds each time its triggered. I could not yet find out when the autosetup is triggered. There is a button for autosetup on the scope but it has no use for me since the scope starts it automaticly.
The autosetup is realy helpfull and gives real good results but it interrupts sampling.
Direct replay from a trace to the build in function generator would be nice.
tautech:
--- Quote from: Wuerstchenhund on September 14, 2016, 05:25:53 pm ---
--- Quote from: nctnico on September 14, 2016, 02:31:08 pm ---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.
--- End quote ---
I'm sorry and maybe I still miss your point but that sounds like a perfect scenario for WaveScan (which is *not* a trigger btw, it's more like a search tool/glitch finder, and it finds stuff that triggers won't). Instead of going through various time base settings I'd just enable WaveScan and let it search for deviations, and then just let it run for a while (5 seconds, 30s, a few minutes, ten days, whatever is appropriate). WaveScan will tell me exactly what went wrong at which point in time.
--- End quote ---
What features does Wavescan offer over a Mask test?
Sounds from what you describe it's much the same thing. :-//
Can it be used over non-repetitive waveforms or a continuous data stream?
David Hess:
--- Quote from: Wuerstchenhund on September 14, 2016, 02:13:24 pm ---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.
--- End quote ---
It was surprising to me but only because I had studied the user manual which implied something very different. Marketing triumphs over engineering.
There really is no alternative to evaluating an oscilloscope in person with a collection of problems to solve.
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--- 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.
--- End quote ---
I did *exactly* that while evaluating a Tektronix MSO5204 and its "advanced toolset" was not able to make the kind of glitch measurement I was interested in which would have been trivial on a oscilloscope with delta delay capability. I could not get it to work and the Tektronix sales engineers could not get it to work although together we managed to crash the DSOs user interface a couple of times. Or does the MSO5000 series qualify as a budget low end DSO?
This experience among others with modern mid-range DSOs has led me to distrust the advertised capabilities of all of them.
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--- 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.
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I think that may have been Tektronix's theory when they released the TDS700 series without peak detection.
With delayed sweep/acquisition capability, the record length is of less importance for making the maximum sample rate available.
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