One, simply because even if your scope achieves that magical 1M updates/s then you're still blind almost 90% of the time. Which means you still miss most of the information in a dynamic signal.
Still pushing that horse? You're misleadingly trying to make an equivalence between waveform update rate (drawing things to the screen, like building an eye diagram or histogram) and acquisition rates (dumping data to memory for later retrieval, often separately called segmented or sequenced acquisition to differentiate that).
Actually, it yourself who (still, as I remember we had this discussion in the past) gets confused.
You mix the waveform update rate with the screen refresh rate, which are two unrelated things.
The screen refresh rate (i.e. the rate at which the display gets updatd) is usually down to 60Hz on a modern scope (and that includes all these high update rate DSOs such as the DSOX3kT).
The waveform update rate (i.e. the rate at how often the scope can update its waveform record) is different. This is the trigger rate, and contains the whole acuisition as well as the subsequent blind time a scope needs for re-arming and processing.
As to segmented/sequence mode, this is a specific mode where the sample memory is chopped up in small blocks (segments) so the long scope memory can be used for a set of short memory acquisitions, thereby increasing the waveform/trigger rate while being able to make some use of deep memory.
Also, segmented mode is pretty irrelevant when we using scopes for RF work.
Its as stark as the difference between "filing" documents to the in-tray, or reading them.
Not sure what you're on about "filing documents" here.
It's not just car analogies that suck, that's for sure.
You've never been able to show any substantiated claim of Lecroy scopes achieving high waveform update rates, only fast trigger rates, which they openly and honestly specify:
Well, I certainly did before my extended absence, as we had this discussion before (more than once).
And I'm sure I did already present this:
I'm not sure what this is to you, but I can see a LeCroy scope pushing a trigger rate of in excess of 1M waveforms/s in NORMAL mode (although it's in WaveStream mode which is an analog-style persistence mode where update rates are maximized).
Also you try and link some arbitrary update rate and blind time together, when that only applies for specific conditions and overheads, this magic 1,000,000 updates/second you seem fixated on does not imply any specific blind time. Yes, the major brands do have a blind time around 90% under the conditions which they hit their peak rates, but that is not applicable across other conditions, and is not some fundamental barrier. If the waveform update rate is 1,000,000 per second, the blind time in undefined, other information is required to determine it.
OK, I'll bite one last time.
The Waveform Update rate (which is identical with the Trigger Rate) is a measure of how many times a scope can update its waveform record. The blind time which follows the acquisition process is a major (actually, the largest) part of the sequence which is the reciprocal of the waveform update rate. It's as simple as that.
I use the 1M wfms/s figure because this is roughly the maximum any scope as of today can achieve (actually, it's slighly higher, but 1M wfms/s is close enough), and it's simpler just taking the max figure when talking about high waveform rate scopes. I thought that was clear, but I guess it's not.
Now as to the blind time: yes, it does vary by scope, and also depends to a certain extend on the memory length and timebase setting used for the acquisition. So you got at least this one right.
There are a couple of things you miss, though.
First, the blind time example I gave was not only rough estimate, i's also a percentage figure. And for a given update rate (like, for example, 1M wfms/s) this percentage figure doesn't vary a lot between scopes. So if you really want to nitpick you can of course argue that it may not be exact 90%, it could well be 93%, 89%, 87% or something else, but at the end of the day the fact remains that at that such high update rates the blind time of any scope available today will always be *vastly* bigger than the acquisition time.
Which means relying on excessively high update rates to capture rare events has roughly a 1 in 10 chance that your scope actually sees it.
Secondly, yes, you can certainly reduce the percentage the blind time presents in the wavform update cycle. You just have to increase the acquisition time, either by lowering the sample rate or by increasing the sample memory. Eventually, your blind time will be smaller than your acquisition time. But then your waveform rate will also have dropped like a rock. And, even when it's smaller, there is still a blind time where your scope will miss events between acquisition cycles.
Which means relying on repeated updates to capture rare events is still a gamble, even your odds may have increased (e.g. 9 out of 10 chance your scope sees it). However, if you can increase the acuisition time to capture your period of interest in one acquisition, and then set a trigger for the event of interest, your the odds of your scope seeing the event will be 100%.
Home
Help
Search
Login
Register
