I am attempting to capture the Lown wave form generated by a defibrilator analyzer. This frequency of this wave length is approximately 200 Hz in length. To do this I have been discharging the defib through a defibrilator analyzer. The analyzer has an output port that allows a BNC cable to send the resulting signal to a scope. First, I tried using a 100 MHz Tek 2235. This displayed the lown wave form in all of its glory but only for an instant. I decided then, to use a digital 60 MHz 2 GB/s Tek TDS 210. This scope is able to capture the image but it shows a ton of interference on the upward portion of the pulse. I tried swapping out the BNC cable and the defib analyzer to no avail. What can I do to remove or filter out the interference?
This is just a supposition. I know that TDS210 had a ground issue in circa 1997 (not very sure about the date), yours may be one of those. Try to connect the ground terminal of the scope (one of the BNC ground or the probe compensation outlet ground) directly to the DUT ground using an adequately sized cable (2.5 squared mm should be ok).
Many of the TDS2xx series are IMHO some the worst DSO designs ever to hit the market. I flat-out refuse to use them. The TDS2xxx are a little better but lack any serious sample memory depth. Get a better DSO. I do this stuff with an Instek GDS-2204 with 25K buffer depth versus the paltry 2.5K on the Teks. The best of them all is probably the new Hameg Analog/Digital combo which AFAIK offer a whopping 1M.
And as Massimo mentioned the TDS2xx serious often has horrible noise performance. A TDS220 once had me fooled. The 40/80kHz noise I could not explain ended up coming out of its own power supply or backlight inverter. I never used that scope again and advised the client to ditch it and get a "real" scope off Ebay. Which they did.
Tek seriously needs to think about either hiring some of their older folks back or seeking external consultants. Else the Asians are going to eat their lunch. I mean, this ain't rocket science. I captured my first defib discharge pattern in the early 90's with a rather old Philips scope and the quality was good enough for the TUEV guys to bless it.
I'd give the little Teks one credit though: They are very portable. My Instek is longer and heavier. However, IMHO it's better.
No, I used and still use some TDS210, and at home I own one TDS2002 and an older portable THS710. They have nothing to compare to the Agilent 6000 series or the Tek
3000/5000 series. Those series are the "Rolls Royce" of the DSO kind and have great performance, but if you need a low priced scope the TDS2xx(xx) series can be a good choice, I guess.
Tek recalled the TDS2xx and patched the ground problem, and now the TDS210 I use always shows the right shapes also in very noisy industrial environments.
About the 40kHz issue, I had a bad experience few years ago working on a project where I had very low signals to amplify, and it took a lot of time to realize that the source was that noisy display backlight!!!
One other issue of the TDS2xx(xx) series is the BNC connector, they easily crack their mounting pins (usually the pcb mounting BNC connectors have 4 pins, while the type used by Tek into the TDS2xx scopes has just two).
About the memory depth, you are right it isn't so deep, but you should admit that in most cases you use a DSO, it doesn't matter to enlarge the waveform and look for its sporadic glitches.
This is true, it's obvious that having more memory depth gives you great advantages analyzing sporadic glitches. But on the other hand, here we are talking about a repetitive signal as the Lown wave of the defibrilator, suggesting Ed to change is scope for this pourpose is a little too much I guess, or not?
I'd call that an embarrassment. Why was it not caught in a design review? If we ever did that in medical electronics the FDA would have us over the barrel.
Same thing, embarrassing. Why was this not caught in in-house tests?
When the Instek arrived I was positively surprised by the rock solid feel to it. Almost like after I bought my first Japanese car where the stick-shift and everything else has this feeling of exactness and precision. Instek could have been a little more careful with translations though. It's nice that the scope masters umpteen languages but some phrases sound a bit rough. For example when you want to run it via a laptop and forget to plug in the USB cable: "DSO not connect".
For me that's life. I get stuff from clients, designed by others so I don't know much about the history. "It behaves erratic sometimes, could you find out why?" Also, with the measly 1K or 2.5K of some of the Tek boxes I might as well forget all my pulse echo tests. Remember that delayed trigger has been left out of many DSOs. Whatever possessed them to remove delayed trigger I'll never understand. It only takes one counter, and maybe a 2nd one for hold-off. Dirt cheap, or since they usually have a large FPGA in there anyway it would be free. But no, they took it out.
Uhmm... I'm not sure what's the meaning of this group.
I believed it has been made to help the technicians > First, I tried using a 100 MHz Tek 2235. This displayed the lown wave
And then he wrote again:
So, I imag>Remember that delayed trigger has been left out of many DSOs. Whatever
Well, I don't know how much time you spent on your TDS210, but with my TDS2002 (but the TDS210 has the same feature too) I can set the horizontal position to 20ms using a slow horizontal scan speed, and then increase the horizontal scan speed to 5ns and see what happened
20ms after the trigger. I'm not sure what you could see with an analog scope with that settings. I used for about 10 years an analog scope with the delayed time-base, but with the introduction of DSO I thanked God because now I can see details invisible before (my old scope had not the CRT's phosphor with the analog memory feature). I also had to deal with FPGAs in my career, but I used logic state analyzers with them, I have one with 48 channels to troubleshoot complex logic. I repeat, there is no doubt that the TDS2xx is not the DSO's state-of- the-art , but it's a good low priced substitute of the older analog scopes, and the Instek is too, I'm sure.
Anyways, this is the last message I write about this futile discussion (futile for Ed who is the owner of this thread, I mean).
If Ed will ask again for an aid dealing with this issue, I'm very glad to help him (if I could).
On Sat, 16 Feb 2008 13:59:51 -0800 (PST), Max65 wrote: [snip...snip...]
It's the price of being an early adapter. The TDS2xx-series were (AFAIK) the first "budget priced" real-time DSOs. FWIW, I got a TDS220 for home use, back in the day, and -- probably because I'm pure of heart or something -- have not had any of the various issues discussed in the thread, so they certainly weren't all junk.
I would simply take a different approach. I suggest using a studio grade (isolated) audio digitizer feeding the PC directly. A PC can ingest that data rate smoothly and continuously for hours at a crack. The resulting data might well please you.
Alternatively there are reasonable low cost data acquisition cards that include DC response and great isolation / differential measurement inputs.
Well, he did not give us enough detail about the unwanted noise. It usually helps to identify what that noise is and a scope with better resolution can help. One good method would be for Ed to post a screen shot. Some of the lower end TDS don't have a data interface but a camera shot would do as well.
Depends on how fast his glitches are.
Storage of one-time events is certainly not the domain of analog scopes unless, as you said, you've got a storage tube. I have that here but the problem is that they fade with age.
As for delayed trigger many, for example the TDS220 we've used, didn't do that. I hope that some day a guy from Tek reads in groups like this and puts a real delay-trigger back in. It's so cheap and easy with DSO.
Nothing futile with realizing the limits of his tools and maybe borrow a better one for a few hours. I've had that at clients where, for example, we suddenly realized that a particular noise had the pattern of a cell phone burst. With the scopes they had it could not be resolved.
I share your opinion, he should better explain us the problem, but it could be he well knows that the problem wasn't real but just
It had but as optional device, as for the advanced triggers feature, while the older portable THS7xx had instead as default(?!?!)
I don't believe he have really seen any, and I believe that the heart of an human doesn't matter of any nano seconds glitches (do you?) I believe he just seen
I'm not sure what do you mean (excuse me, but I'm italian and english is not my native language), Tell me if I understood: your TDS220 doesn't let you move the horizontal position trigger out of the acquisition window? May be I confused it with my own TDS2002, it has the "window" and the "window zone" functions too that are similar to the delayed time- base. Anyways, tomorrow I'll be at office, there I still have one TDS210 and I try with it and tell you about.
I don't wanna to confuse him. I explain: if he read all what we wrote above, he could believe we don't really have care of his problem, but just talk about DSO (that's what we did ideed).
Their older "Scope Stations" had the feature, AFAIR.
I think he is looking at a defibrillator discharge curve. Minor glitches wouldn't matter but large spikes in there can become a serious problem.
Bella Italia. Fond memories from several vacations there. Those are the vacations where you don't really want to leave anymore at the end.
It's similar on the Instek GDS2204 here in the lab, you can move outside the window but pretty much all those scopes do not have essential support functions such as hold-off. IOW the trigger blows apart when you have multiple bursts.
But my main gripe with the TDS220 is the fact that it showed noise that really wasn't there. Cost me and my client almost half an hour until I discovered that it came out of the scope itself. That just isn't supposed to happen. That same week they bid on a Tek 2265 on Ebay and got it.
Well, that's what newsgroups do. It's a discussion just like in a pub. And a lot of great product ideas and problem solutions happen in pubs ;-)
I had been in California (you are there I guess), and I can tell the same about your land and people (may be the old told story that "the grass on the other side is always greener"?) ;)
I check the TDS210, and it has too, the hold-off can range from 500ns to several seconds. The real issue is the complex method used to set it, since you need to go into the Horizontal menu select its soft key on the border of the screen and use the trigger level knob to adjust (if you selected a quick horizontal scan, you may waste a lot of time to reach slow hold-off times).
That could be the issue they fixed later in '98(circa). I did the self cal this morning and it shows just a noisy trace of 2mV (when set to peak detect mode which is the worst case). The 40kHz issue It was due to the LCD discharge lamps used into the LCD display of the DSO. But it seems to be a common issue for LCD instrumentation with cold cathode backlight. The day before yesterday, I did a check on my instrumentations and I found that almost all of them have the same problem. The only one which haven't the problem despite it uses the cold cathode backlight, is the Rohde & Schwarz SME03 generator. I don't really know how they solved the problem, may be they put the lights far from the border and EM shielded them. Anyways, the CRTs emit EM fields too, but on other frequencies. When I had that problem, my inexperience was real culprit. That time, I had some unshielded inductor into the front-end of a circuit used to detect a very small laser pulsed train of 1.5ms in duration (just 750 microJoules), over a 300x300mm solar panel. I placed the circuit on the same bench where the DSO was... and I wasted a lot of my time dealing with it (I feel stupid now).
Have a great day, and take a intense look to the sunny California landscape to me (lovely place). Massimo
It has hold-off? That's a surprise. We could not make that work on the TDS220.
Yes, that's the weird way almost all DSOs have to be set for scans far outside the main window. It would have been nice to include a real delayed trigger. Except for some modest R&D time it would cost next to nothing.
I had suggested that to the designers of my scope in Taiwan. They seemed quite interested in the beginning but no new firmware has been released yet. But as the Chinese say, patience is everything.
On self-cal it doesn't show because on the Tek series it is a conducted noise problem, conducted when the scope probes are attached. And that would have been rather easy to fix or completely avoid in the first place. My impression is that the design review process up there wasn't as thorough as it used to be. Or maybe because the old folks aren't there anymore.
That's because they also make (or at least used to make) defense gear. Mil stuff must pass much stricter emissions than lab or consumer gear, or even medical. So these guys know how to do things right. And it's easy:
Do the backlight strictly differential and common-mode choke the heck out of that. Ferrite is still cheap (probably because it's not oil-based...). If radiated noise is an issue lay a fine see-through mesh over the screen. Ok, it may cost a 20% drop in translucency but on the other hand gives the unit that robust "military" look. Or just use a better display. The Instek scope here has a TFT and although I turned its brightness way down you can still see it at the far end of the hallway. I find I get much less tired in front of that scope compared to some of the TDS.
Stuff like this happens to all of us, when we quietly mumble "I hope nobody saw that". Especially with consultants who sometimes are believed to have guru status. And we are not gurus.
And have a nice glass of Chianti Classico for me ;-)
My wife made Tiramisu yesterday. Can't wait. Maybe I can talk her into making Zuppa Inglese after that. I miss the Italian restaurant we had in our little town back in Germany.
Hi Joerg, yesterday night I tried to send you a private reply, but this morning I realized that your address should refer to such kind of anti-spam service. I wrote you the private msg to avoid this thread to grow up with non electronics related messages.
May be your one was an early fw machine.
I hope you'll be luckier than me with it In 1998 I discovered a bug into the frequency counter of a Korean made test-set. I contacted the developers and explained them the problem (they had missed the carry of the least significat word in the reciprocal computation of the period when the counter was measuring very low frequencies). They were lovely and willing people until I explained them the problem, and promised me a new updated cpu (they didn't have any ISP features in their counter, and used an eprom based microcontroller), but when it came the time to send me that updated device, I lost any contact with them (I'll never buy an instrument from that factory).
My own never shown this issue, may they fixed later yours.
I very well know how R&S works, a good friend of mine worked for a long time at their service department here in Italy.
You are right, but may be they considered easier to suggest the user to keep the DUT away from the scope screen, so they supplied you the scope with two 5 feets long cabled probes!!! ;-)
Nothing is more correct than you say. Almost all my skillfulness is the result of experience on the field, which has been made of mistakes and their fixup!
To be honest, I prefer a good glass of Lambrusco which is sweeter than Chianti, but you should now that I'm not a wine expert (to be more honest I know almost nothing about wines) I'm from the North West of Italy, here we have the Barbera, but I don't like it so much. I prefer white wines to the reds, so many friends of mine tell me to continue to drink coke, that's better for me!
There is no anti-spam, just delete "notthis" and "removethis" and it'll work. Newsgroups are copied into the web so much that it has tio be done to avoid spam robots. Or just use jsc _at_ ieee _dot_ org.
It's ok to discuss equipment related stuff here. In other technical groups they even discuss politics but that can get ugly. Some of the barbeque recipes are good though.
I think most were late 90's.
Yes, got to be careful. The scope works as expected, only a few language issues but on the other hand they crammed an enourmous amount of languages in there. Including Italian :-)
Problem is, the long scope probes did not fix it. No, to me that is a hardcore design flaw. Not supposed to happen at a company of this reputation.
I love a good Barbera. But first there has to be a good cup of espresso, every evening. I believe you guys call it cafe.
Yes, I really do have to watch that. But what can you do if the smell wafts over from the kitchen?