Author Topic: Tek tds 3054b vs tds 744a  (Read 31919 times)

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Offline cncjerry

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Tek tds 3054b vs tds 744a
« on: October 29, 2014, 06:40:16 am »
I posted this up on the tekscopes forum, no interest, so I thought I would try here.

I have a 744a that I love.  Yes, it is large, clunky, etc. but mine is a beauty, excellent shape, calibrated, etc and performs perfectly.  It has a crystal clear display and high contrast.  Having Glaucoma where lights bloom, the contrast is important to me.  I also got it for the cost of the probes alone (or better).

I recently had the opportunity to purchase a TDS 3054b again for a great deal.  I had read a lot about this scope and thought it would have a leg-up on my 744a.  Now I am starting to wonder and I guess the question I have is should I give it more time or is it truly below the 744a in features and functions?

Here's what I've found comparing the two: 

The 3054b is lighter, portable, with a larger display but it doesn't have near the contrast of the 744a.  The colors on the 744a are fully configurable and the 3054b your stuck.  This plays into the contrast again as I have more problems with some colors than others.  The variable DPO is interesting but I prefer the instaVue on the 744a as it uses color to differentiate the signal whereas the DPO uses intensity.  The 3054b has a higher sample rate compared to the 2GS/s on the 744, it has 5Gs/s across all four channels.

The acquire settings are missing hi-res and the average settings are stepped in powers of 2 whereas the 744a has unit variability from 2 - like 9000.   My 744 has the higher capture installed so I get more data as well though I haven't figured out how to get more than like 500 points into matlab.

Unless I am missing something, the 3054b doesn't really do probe compensation like the 744a but it has more splits in the probe pin contacts.

I use the keypad on the 744 a lot so that's gone on the 3054.  My 744 has GPIB where the 3054b has Ethernet which works pretty well. I have fixed IP addresses so my brother can see the scope across the internet.  I can add GPIB pretty cheaply but don't think I need it.

The FFT on the 3054 looks really grainy compared to the 744a.  Also, on the 744a I can set the persistence up higher and get nice impedance plots using a sweep or noise generator.  Haven't figured that out on the 3054 as the persistence doesn't seem to impact the FFT.

I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?  By the way, I do like Agilent scopes, just never see a killer deal.

Jerry
 

Offline AndyC_772

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Re: Tek tds 3054b vs tds 744a
« Reply #1 on: October 29, 2014, 07:09:31 am »
I used a couple of very similar scopes, a 3034B and a 754D, extensively for years, and for the most part I agree with you.

If you have the bench space to make the scope a permanent fixture, then the 700 series has a lot to commend it. I bought mine for home use as a budget alternative to the 3000 that I had at work, and rarely felt like I was using a machine that was second best.

I could have done without the noise and the heat, though. At over 400W, it made my lab an uncomfortable place to work in summer despite my best efforts to keep the place cool. Newer scopes don't have the same effect.

The reason I eventually sold it, though, was fear for how long it had left to live. The 'D' series models don't suffer the same capacitor rot as earlier units - and if you've not had the caps changed already then do it now! - but they do still have a CMOS memory module with a battery that'll be well past its expiry date by now.

When I started using my own gear to make a living rather than just as a hobby, I decided I couldn't afford to risk it dying in the middle of a customer job, and started looking around for newer alternatives. Now I have an Agilent 3000X with all options enabled, and other than the fact that I miss the equivalent-time modes, I couldn't be happier with it.

Offline Smokey

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Re: Tek tds 3054b vs tds 744a
« Reply #2 on: October 29, 2014, 07:19:35 am »
After using the TDS3034B at work for years, the only real complaint I have is the small sample memory.  That's about the only thing that has gotten in the way of what I needed to do.  I've always thought the screen looked really good.  Well, ok and the floppy drive not being convenient sucks too.  I guess you can replace the floppy with a floppy-USB adapter thing, but I just grab screen shots from the Ethernet connected computer.
 

Offline cncjerry

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Re: Tek tds 3054b vs tds 744a
« Reply #3 on: October 29, 2014, 07:41:52 am »
I'm going to replace the battery in my 744a now that you mention it.  Supposedly the 744 and 754 didn't save the cap problem like prior models.  Having said that though, the battery will die tonight and wHen I open it up the caps will pour out.

I can't believe how much you get for so little with these old scopes.  If people sat down with them and saw the features I think most would be impressed.  I see 5xx, 6xx and 7xx scopes on craigslist all the time for under $600.

The 3054 screen is nice but I prefer the high contrast of the 744, at least right now.  I guess I thought the 3054b would be better than it is, maybe it will take some time to get used to it.

These are the colors that I can see the best with the vision problems I have.

 

Online nctnico

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Re: Tek tds 3054b vs tds 744a
« Reply #4 on: October 29, 2014, 11:22:12 am »
Yeah make me regret selling my TDS744A  :'(
I don't think the TDS3000 series are a good replacement due to their short memory. Did you look at the TDS5000 series? Or look at Lecroy; some say their higher end scopes are more geared towards signal analyses but I have no personal experience to back that up.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #5 on: October 29, 2014, 12:10:04 pm »
I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.
 

Offline MarkL

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Re: Tek tds 3054b vs tds 744a
« Reply #6 on: October 29, 2014, 01:31:38 pm »
The 3054 screen is nice but I prefer the high contrast of the 744, at least right now.  I guess I thought the 3054b would be better than it is, maybe it will take some time to get used to it.

These are the colors that I can see the best with the vision problems I have.

I have a TDS3054 I bought new 15 years ago and I never noticed how dim the display had become over the years.  I was able to replace the CCFL tubes with new ones and it made a huge difference in readability.

You can replace the CCFL tubes as slide-out FRUs, NEC part #65LHS–3L, or solder in bare CCFLs.  I did the latter with tubes from ccflwarehouse.com, part #CC26153.  There are two tubes and the display in your "B" version uses the same CCFLs according to the Tek service manual.

I've never used a Tek TDS7xx series, so maybe it has a better display anyway, but thought I'd point this out.
 

Offline tinhead

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Re: Tek tds 3054b vs tds 744a
« Reply #7 on: October 29, 2014, 01:43:36 pm »
you can even get more on tds700A series, with 4 resistors (in your case from 744A to 784A only one resistor on acq board) one can get 4GSa/s for single channel and 2GSa/s when 1or 2 and 3 or 4 ch enabled. The bandwidth increase to 1GHz must not work always.

One have of course to let calibrate somewhere (the cheapest way) or did it yourself (TDS700A Field Adjustment Software PN_063260100, NI GPIB controller and some signal gens, counters necessary to do that!).

In principle it does works as well when you burn the calibration data from other TDS784A, but only the missing
data for 4GSa/s not everything, it will not work 100% exact but sufficient. On the TDS700A series the call data is stored
in two X24C02 EEPROMs on bottom side of ACQ board (U1055, U1052). The data can be duped via GPIB, i wrote once
small app to dump that data, see attached code for TDS7x4A models (works similar to tektool from tek forum).

These board ID resistors (R1061<->R1064), whit which the model can be set, are near these EEPROMs as well. Soldered is 0.

TDS784A: 7,   0 1 1 1
TDS754A: 8,   1 0 0 0
TDS744A: 6,   0 1 1 0

interessting that these resistors are not on the TDS500B series schematic (well, they are marked as "exluded from").


on CPU board there are ID resistors as well (R12, R13, R15, R17). As far i remember there was no need to change
them when model was set on ACQ board to TDS784A.

744A - 12,17=0, other 1      0 1 1 0
754A - 17=0,    other 1      0 1 1 1

Btw, in principle one could take an TDS540B and change it to TDS784A, sure it will be still no color
(except on external monitor or custom display), but from sampling and bw point of view it would work.
I always liked these TDS700 series and wrked with them for long time, even if they loud and clunky.

And before i forget, similar hacks (with model change) are possible on TDS600B, TDS700C and TDS700D as welll,
but please don't ask me for details, use google to search for pcb pictures and you will find the differences.

« Last Edit: November 01, 2014, 12:16:18 am by tinhead »
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Offline MarkL

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Re: Tek tds 3054b vs tds 744a
« Reply #8 on: October 29, 2014, 02:12:39 pm »
I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.
Well,  there must be something to the TDS3000 series.  Crazy prices aside, used TDS3054x units are selling for 2x to 3x the TDS744 on ebay.

I wouldn't put the TDS3000 series in the entry level category, but if you're looking for entry level I wouldn't be buying one of those anyway given the value you can get on some of the Rigols brand new.
 

Offline cncjerry

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Re: Tek tds 3054b vs tds 744a
« Reply #9 on: October 29, 2014, 02:28:25 pm »
I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.

Wait a minute, who's missing what here?  A 3054b an entry level scope?  :-) Don't make fun of my kids...

Granted it is old, but the price this sucker went for in it's day puts it a few notches up over entry level scopes.  I keep staring at this thing wondering who would have paid $8k for one new because as I struggled with above, when this was new the 744A and 754A weren't that old.   I still see 3054b's listed for 5k or even more.  Locally there are two 3052's that are listed at $5k and 5.6K and another 3054 (non b) that was listed at 6.6K.  I know nobody pays that much, but I haven't found one that works for under 2k.

 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #10 on: October 29, 2014, 03:25:44 pm »
I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.

Wait a minute, who's missing what here?  A 3054b an entry level scope?  :-) Don't make fun of my kids...

Well, it's an upper entry-level scope ;-) The TDS3000 has always been on the lower end of Tek's offering, I'm not sure why this surprises you. In terms of capabilities it's a pretty primitive scope, low memory, poor maths and FFT, and that's about it. We still had several of them were I worked approx 10 years ago, they were fine for basic tasks but hardly luxurious in terms of capabilities or performance. Their main advantage was in their portability and the optional battery.

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Granted it is old, but the price this sucker went for in it's day puts it a few notches up over entry level scopes. I keep staring at this thing wondering who would have paid $8k for one new because as I struggled with above, when this was new the 744A and 754A weren't that old.

Well, that was then, almost 15 years ago (the TDS3000 came out in 2000; IIRC the TDS744A is probably from around 1995 so quite a bit older), not today. Scope prices at the lower end of the spectrum have come down quite a bit since then. The TDS3000 is roughly where the Agilent DSO-X2000/3000 Series is today, and that is still the lower end of the market. Tek's midrange started with the TDS5000.

Quote
I still see 3054b's listed for 5k or even more.  Locally there are two 3052's that are listed at $5k and 5.6K and another 3054 (non b) that was listed at 6.6K.  I know nobody pays that much, but I haven't found one that works for under 2k.

There's all kinds of old stuff listed at exorbitant prices on ebay and elsewhere. That doesn't mean they sell for that amount, in fact many of the sellers that list kit at insane prices are happy to relist it year by year, waiting for someone stupid enough to buy at their asking price. This is however not specific to Tek scopes, you'll find these sellers for any other kit as well.

I'd say anyone who pays $5k or more for such a scope needs to have his head examined, seriously. $2k for a TDS3054 is still stretching it but I guess for some people it's important that a scope carries the name 'Tektronix', for which they apparently glady pay a premium. But even at $2k a TDS3054 is not really good value for money, considering the other options that are out there.
« Last Edit: October 29, 2014, 09:41:41 pm by Wuerstchenhund »
 

Offline cncjerry

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Re: Tek tds 3054b vs tds 744a
« Reply #11 on: October 29, 2014, 03:58:06 pm »
I agree with some and most of the points from Wuerstchendhund (some kind of dog?) except the comparison to the rigol et al.  Not to start a debate, and all you rigol fans, please note this is my thread, I know all there is to know about Rigol, Owon (have an SDS7102V), and the others.  I've read it all.  I am on the side with the people that think the Rigol hack-ability is a marketing ploy on their part.  Though that doesn't mean it isn't a great scope for the money. 

Also, as to the Agilent which I love by the way, I play with the 2000 series at Fry's every time I go in, I find it hard to believe that scope could keep up with the TDS3054b or even the 744a in the higher speeds.

I can give you 2 recent examples that compare my lower end scope to the lower end (yeah, right) TDS 3054b: 

1) Take a noisy 50mv RMS signal at 400hz.  Feed it into your typical asian scope that cost $500, +/- 100.  Set the coupling for ack and trig to AC and raise the trigger above zero to like .75 the positive peak.  Then take a measurement using their measurement function and tell me if you get the correct RMS value.  I don't on my SDS7102v but do on my 744a and the 3054b.  I also get the correct number on my ancient HP 427a.  On the SDS7102v, which I found to be a decent entry level scope, the signal tracks above zero as I move the trigger up and the RMS value drops.  Now in some ways this makes sense as the scope is triggering on the outlying signals above the zero line.  As there are fewer outlyers than there are correct signals, maybe the RMS should be lower?  Don't know, haven't thought about it much since last night.

2) The other thing I noticed is that with long but high quality 75 ohm cables (about 2M long) when I feed a signal into an old HP 427a voltmeter, that which I was calibrating above, I get more noise on the signal when I attach it to the meter and couple to the sds7102v.  So if I am looking at the signal coming from the generator and it is somewhat clean, then attach it to the old 427a, I see tons of noise;  If I do the same with the TDS scopes, I don't see half that much.  I don't know what this means.  Just found it last night.

These are the fist two inconsistencies I've seen on my sds7102v which I really like for the screen.  It might not apply at all to other entry level scopes.

Jerry
 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #12 on: October 29, 2014, 05:57:55 pm »
I agree with some and most of the points from Wuerstchendhund (some kind of dog?)

"Wuerstchenhund" is the direct German translation of "sausage dog", which in German is actually "Dackel" or "Dachshund".

Quote
except the comparison to the rigol et al. 


Well, when it came out the TDS3000 definitely was (better) entry-level, and so are Rigol scopes. It's certainly a fair comparison.

Quote
Also, as to the Agilent which I love by the way, I play with the 2000 series at Fry's every time I go in, I find it hard to believe that scope could keep up with the TDS3054b or even the 744a in the higher speeds.

I can't see why not. The TDS3000 is a scope of the same class from 14 years ago, and the TDS744A is (if my records are correct) somewhat 20 years old. None of them have any special capabilities or great features. The TDS744A was a very expensive and certainly a good scope at its days but sorry, technology has moved on a bit in these two decades.

Quote
I can give you 2 recent examples that compare my lower end scope to the lower end (yeah, right) TDS 3054b: 

1) Take a noisy 50mv RMS signal at 400hz.  Feed it into your typical asian scope that cost $500, +/- 100.  Set the coupling for ack and trig to AC and raise the trigger above zero to like .75 the positive peak.  Then take a measurement using their measurement function and tell me if you get the correct RMS value.  I don't on my SDS7102v but do on my 744a and the 3054b.  I also get the correct number on my ancient HP 427a.  On the SDS7102v, which I found to be a decent entry level scope, the signal tracks above zero as I move the trigger up and the RMS value drops.  Now in some ways this makes sense as the scope is triggering on the outlying signals above the zero line.  As there are fewer outlyers than there are correct signals, maybe the RMS should be lower?  Don't know, haven't thought about it much since last night.

I never had an Owon (and the ones I've seen made me glad I never bought one), but it's of course possible that there is a bug in how the scope calculates measurements. The Chinese have shown that they can produce decent hardware but in terms of software they still mostly suck.

The other thing is that your example doesn't say enough about the parameters you made the measurements under to determine what the issue was. For example, what was the noise floor on the 50mVrms 400Hz signal, what were its frequency components, what was your scope setup etc. I guess the Owon takes measurements from the screen content so how the scope was setup will have an impact on accuracy. Then there is the bandwidth difference (I assume the Owon os 100MHz? The TDS3054 is a 500MHz scope) which plays into that as well.

Quote
2) The other thing I noticed is that with long but high quality 75 ohm cables (about 2M long) when I feed a signal into an old HP 427a voltmeter, that which I was calibrating above, I get more noise on the signal when I attach it to the meter and couple to the sds7102v.  So if I am looking at the signal coming from the generator and it is somewhat clean, then attach it to the old 427a, I see tons of noise;  If I do the same with the TDS scopes, I don't see half that much.  I don't know what this means.  Just found it last night.

Again, too little details, but it might be that the Owon introduces more noise over the GND connection.

I'm not sure if those tests really show a problem with the Owon or with your setup.
« Last Edit: October 29, 2014, 06:04:47 pm by Wuerstchenhund »
 

Offline cncjerry

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Re: Tek tds 3054b vs tds 744a
« Reply #13 on: October 29, 2014, 06:08:56 pm »
I wasn't implying a problem with the Owon as I said, I like it for the money.  It's just something I would have to dig into.  I had the Owon on Battery without an external ground.  Many things can cause it, just that an unsophisticated user might not have recognized the problem that wasn't evident on the TDS scopes.  So from that perspective the TDS scope justifies itself.  At about 10x the cost used.   


And on that hacking the 744a, is that really feasible?  I wonder if I would get anything out of it.  I seldom work over 500Mhz.  All the bandwidth brings me is noise.
 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #14 on: October 29, 2014, 08:03:43 pm »
Many things can cause it, just that an unsophisticated user might not have recognized the problem that wasn't evident on the TDS scopes.  So from that perspective the TDS scope justifies itself. 

Not really. There's no evidence suggesting that the outcome was because the Tek is the better instrument or that these problems can be avioded by using a TDS3000 scope.

The only reasonable conclusion that can be drawn from this episode is that you'll measure crap if you don't know what you're doing or what the limitation of your equipment are. Simple as that. This "unsophisticated user" would have plenty of opportunities to get the similar crap results with the Tek scope.
« Last Edit: October 29, 2014, 08:05:34 pm by Wuerstchenhund »
 

Offline Smokey

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Re: Tek tds 3054b vs tds 744a
« Reply #15 on: October 29, 2014, 11:38:11 pm »
Fact!
You would be surprised how "smart" a person can be and still be an "unsophisticated user" by overestimating what a piece of equipment is capable of doing. 
 

Online nctnico

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Re: Tek tds 3054b vs tds 744a
« Reply #16 on: October 30, 2014, 02:08:23 am »
Many things can cause it, just that an unsophisticated user might not have recognized the problem that wasn't evident on the TDS scopes.  So from that perspective the TDS scope justifies itself. 

Not really. There's no evidence suggesting that the outcome was because the Tek is the better instrument or that these problems can be avioded by using a TDS3000 scope.

The only reasonable conclusion that can be drawn from this episode is that you'll measure crap if you don't know what you're doing or what the limitation of your equipment are. Simple as that. This "unsophisticated user" would have plenty of opportunities to get the similar crap results with the Tek scope.
Maybe even more. The TDS744A has a boat load of ways to acquire and display a signal. Modern scopes are dumbed down a lot.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #17 on: October 30, 2014, 06:16:12 am »
Fact!
You would be surprised how "smart" a person can be and still be an "unsophisticated user" by overestimating what a piece of equipment is capable of doing.

Indeed. But this really is then an issue with the person and not the fault of the equipment.
 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #18 on: October 30, 2014, 06:27:26 am »
The TDS744A has a boat load of ways to acquire and display a signal. Modern scopes are dumbed down a lot.

The TDS744A's manual only lists these:

  • Sample Mode - the normal sample mode
  • Envelope Mode - collecting Extrema over multiple acquisitions
  • Average Mode - collecting average over multiple aquisitions
  • Peak Detect - essentially Envelope Mode over only two acquisitions
  • Hi-Res Mode - oversampling to increase the vertical resolution

It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?
 

Offline David Hess

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Re: Tek tds 3054b vs tds 744a
« Reply #19 on: October 30, 2014, 07:13:54 am »
The TDS744A's manual only lists these:

  • Sample Mode - the normal sample mode
  • Envelope Mode - collecting Extrema over multiple acquisitions
  • Average Mode - collecting average over multiple aquisitions
  • Peak Detect - essentially Envelope Mode over only two acquisitions
  • Hi-Res Mode - oversampling to increase the vertical resolution

The TDS744A manual is very specific that peak detection occurs over one acquisition.  Two adjacent intervals are used to store the high and low values which I assume halves the record length.  Envelope mode uses multiple peak detection acquisitions.

InstaVu (DPO mode) combines with the sample or peak detect acquisition modes.

FastFrame (segmented memory) combines with most or all of the acquisition modes.

Depending on how one looks at it, that could be considered 12 different modes or too many ways to misconfigure the oscilloscope and confuse the user.

Quote
It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

A lot of modern DSOs inexplicably lack peak detection.  Maybe the designers figure having long record lengths makes it unnecessary.

 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #20 on: October 30, 2014, 10:24:57 am »
The TDS744A manual is very specific that peak detection occurs over one acquisition.

That is not correct. From the TDS 684A, TDS 744A & TDS 784A Digitizing Oscilloscopes User Manual (070-8331-02 from 1994) page 3-22:

Peak Detect Mode. TDS 700A models only: Peak Detect mode alternates between saving the highest sample in one acquisition interval and lowest sample in the next acquisition interval. Peak Detect mode only works with real-time, noninterpolated sampling.

The manual says the following to Envelope Mode:

Envelope Mode. Envelope mode lets you acquire and display a waveform record that shows the extremes in variation over several acquisitions. You specify the number of acquisitions over which to accumulate the data. The oscilloscope saves the highest and lowest values in two adjacent intervals similar to the Peak Detect mode. But Envelope mode, unlike Peak Detect, gathers peaks over many trigger events.

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InstaVu (DPO mode) combines with the sample or peak detect acquisition modes.

InstaVu is a Tektronix marketing term so it's obvious it's not found in other scopes. It's simply persistence mode with Peak Detect switched on.

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FastFrame (segmented memory) combines with most or all of the acquisition modes.

FastFrame again is a Tektronix marketing term. Segmented memory which can be combined with other modes of course exists in many modern scopes.

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It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

A lot of modern DSOs inexplicably lack peak detection.  Maybe the designers figure having long record lengths makes it unnecessary.

I've seen Peak Detect (which, as we hopefully have now established, is simply Envelope mode over only two aquisitions) on some newer scopes, particular those without Envelope mode.

Better scopes have Envelope mode and you get Peak Detect by setting the number of aquisitions to two.
 

Offline Ivan7enych

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Re: Tek tds 3054b vs tds 744a
« Reply #21 on: October 30, 2014, 10:41:10 am »
Hi-Res Mode in Tek 744A produces 16bit samples, and I can transfer this 16 bit data via GPIB to analize it. That mode is very helpful to analyze slow and low voltage signals

My Rigol 2072 has Hi-Res Mode, but it is always 8bit.
 

Offline Ivan7enych

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Re: Tek tds 3054b vs tds 744a
« Reply #22 on: October 30, 2014, 10:42:30 am »
you can even get more on tds700A series, with 4 resistors (in your case from 744A to 784A only one resistor on acq board) one can get 4GSa/s for single channel and 2GSa/s when 1or 2 and 3 or 4 ch enabled. The bandwidth increase to 1GHz must not work always.
Thank you very much for this detailed info! I'll try this mod on my 744a unit.
 

Offline Wuerstchenhund

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Re: Tek tds 3054b vs tds 744a
« Reply #23 on: October 30, 2014, 10:53:29 am »
Hi-Res Mode in Tek 744A produces 16bit samples, and I can transfer this 16 bit data via GPIB to analize it. That mode is very helpful to analyze slow and low voltage signals

Most better scopes have high res modes that increase the sample size by an additional 2 or 3bit, which is the limit as to what is sensible in a scope with 8bit ADC hardware. For everything above that there are true (and fake) 12bit scopes.

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My Rigol 2072 has Hi-Res Mode, but it is always 8bit.

If it's still 8bit, what makes it Hi-Res then?

« Last Edit: October 30, 2014, 12:10:41 pm by Wuerstchenhund »
 

Offline David Hess

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Re: Tek tds 3054b vs tds 744a
« Reply #24 on: October 30, 2014, 01:54:58 pm »
The TDS744A manual is very specific that peak detection occurs over one acquisition.

That is not correct. From the TDS 684A, TDS 744A & TDS 784A Digitizing Oscilloscopes User Manual (070-8331-02 from 1994) page 3-22:

Peak Detect Mode. TDS 700A models only: Peak Detect mode alternates between saving the highest sample in one acquisition interval and lowest sample in the next acquisition interval. Peak Detect mode only works with real-time, noninterpolated sampling.

Acquisition interval (Tektronix still uses this term.) is not the same as waveform acquisition.  When the real time samples are decimated for sample mode, peak detect mode, or high resolution mode, they produces acquisition intervals within the display record.  In peak detect mode, two adjacent acquisition intervals within the display record are used to hold the minimum and maximum values for the total duration of time those acquisition intervals represent.  This allows peak detection to operate on a single and every waveform acquisition:

From the same manual on page 3-21:

Provides the benefits of enveloping with the speed of a single acquisition.

And page 3-20:

Sample (the mode most commonly used), Peak Detect, and Hi Res modes
operate in real time on a single trigger event, provided that the oscilloscope can
acquire enough samples for each trigger event.


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The manual says the following to Envelope Mode:

Envelope Mode. Envelope mode lets you acquire and display a waveform record that shows the extremes in variation over several acquisitions. You specify the number of acquisitions over which to accumulate the data. The oscilloscope saves the highest and lowest values in two adjacent intervals similar to the Peak Detect mode. But Envelope mode, unlike Peak Detect, gathers peaks over many trigger events.

Which means peak detect works over one trigger event and a single acquisition while envelope mode operates over two or more trigger events and multiple waveform acquisitions.  You can use peak detection with a single shot acquisition.  Envelope mode (without InstaVu or DPO) is done in post processing.

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InstaVu (DPO mode) combines with the sample or peak detect acquisition modes.

InstaVu is a Tektronix marketing term so it's obvious it's not found in other scopes. It's simply persistence mode with Peak Detect switched on.

It is neither of those things.  When operating as a DPO, a histogram is generated in real time during decimation.  This is separate from persistence which is a separate step done after the acquisition record is transferred to the display record.  More modern DPOs may combine these steps although this may make them slower than the TDS744A.

It has been a while since I have used one of these oscilloscopes so I do not remember exactly how peak detection interacts with DPO mode but as I recall, it generates an envelope instead of a graded index.  This combination of modes always seemed pointless to me but at slower time/div settings I suppose it has utility.

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It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

A lot of modern DSOs inexplicably lack peak detection.  Maybe the designers figure having long record lengths makes it unnecessary.

I've seen Peak Detect (which, as we hopefully have now established, is simply Envelope mode over only two acquisitions) on some newer scopes, particular those without Envelope mode.

We have not established it.  If peak detection required more than one acquisition, then it would require more than one trigger and would not work on a single shot acquisition.  There would also be nothing to distinguish it from envelope mode.

Are you thinking of peak detection as Rigol defines it on their older DSOs where they confound peak detection with envelope detection?  They work the way you describe when in peak detection mode which on a Tektronix would be envelope detection mode.

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Better scopes have Envelope mode and you get Peak Detect by setting the number of acquisitions to two.

Better oscilloscope have both modes and on some, you get peak detect by setting the number of envelope acquisitions to one.

Some cheap DSOs have envelope detection without peak detection because the later requires dedicated hardware.
 


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