Tektronix TDS744A

[ebclr]

On this scope the tube is a real hifh speed scope tube, or is only like a color tube like the ones on color TV monitor showing low speed signal that was handled on the digital processor and display on a low speed CRT monitor

[nctnico]

It is a DSO so it shows what has been sampled before.

[TAMHAN]

Sampling. But it uses InstaVu, so it has a more Phosphorish view to it.

[nctnico]

Don't expect too much from Instavu! IIRC it is just a false color display with 16 different colors.

[SaabFAN]

Yes to not expecting too much from InstaVu - I've seen it in a video on Youtube and it appeared sluggish as hell.

Tektronix later invented the Marketing-Term "Digital Phosphor", which simply is different levels of intensity assigned to how many times a value is read by the ADCs in a second.
There is no direct analog path from the inputs to the Display-Tube (maybe except for some common ground-connection ). I believe there are even LCD-Conversion-Kits available that replace the tube with a VGA-Compatible flatscreen.

[TAMHAN]

Hello,
afaik, InstaVu and / or DPO is, by its nature of averaging, something you "let loose" and wait for it to catch that glitch or to generate the waveform picture you desire. When that looks nice, you screendump it

More info on the technical way:
http://www.evaluationengineering.com/new-analog-equals-digital-sleight-of-hand
http://www.hit.bme.hu/~papay/edu/DSOdisp/gradient.htm

A critical point on DPO, which essentially is InstaVu 2 and even was labeled as that on some TDS754D protos:
http://www.edn.com/design/test-and-measurement/4342340/10-08-98-Gloves-Of

[nctnico]

The practical use of waveforms/s has already been discussed at length and the conclusion is that a high number of waveforms/s is based on marketing hype and FUD. A DSO shines at single event capturing to catch a glitch and the best thing is that you don't need to stare at the screen. Set the DSO up, go out for a walk and see what it caught when you get back.

[TAMHAN]

Not necessarily, with all due military respect. I use the DPO a lot to create histogramish diagrams showing how a process behaves over multiple iterations of something. For example, a process computer reacting to an impulse...how much time delay there is, how equal the time delay is, etc. Simply set up the DPO, and let it aquire them waveforms over time...

Sadly, my DPO currently is down...so I cant make a video.

[andy2000]

I've seen two versions of the TDS744A.  The earlier firmware version has a very long persistence on Instavu which makes it almost useless.  The newer version behaves a lot like DPO mode on the later scopes.  How useful you find it will depend on what you're doing.  I've never used it to find glitches, but just try and view a complex waveform like a full frame of a video signal without something like DPO. 

[KE5FX]

The practical use of waveforms/s has already been discussed at length and the conclusion is that a high number of waveforms/s is based on marketing hype and FUD. A DSO shines at single event capturing to catch a glitch and the best thing is that you don't need to stare at the screen. Set the DSO up, go out for a walk and see what it caught when you get back.

A modern DSO has to be able to eliminate the need for an analog oscilloscope.  For that, you need a large number of waveforms per second.  The bigger the better.

[timb]

I've seen two versions of the TDS744A.  The earlier firmware version has a very long persistence on Instavu which makes it almost useless.  The newer version behaves a lot like DPO mode on the later scopes.  How useful you find it will depend on what you're doing.  I've never used it to find glitches, but just try and view a complex waveform like a full frame of a video signal without something like DPO.

On my TDS754C, you can change the InstaVue persistence time. It can be set from 32ms to 10s or infinite. (While the non-InstaVue persistence mode only goes down 250ms.)

It's *very* useful.

[andy2000]

I've seen two versions of the TDS744A.  The earlier firmware version has a very long persistence on Instavu which makes it almost useless.  The newer version behaves a lot like DPO mode on the later scopes.  How useful you find it will depend on what you're doing.  I've never used it to find glitches, but just try and view a complex waveform like a full frame of a video signal without something like DPO.

On my TDS754C, you can change the InstaVue persistence time. It can be set from 32ms to 10s or infinite. (While the non-InstaVue persistence mode only goes down 250ms.)

It's *very* useful.

I forget the exact number, but the minimum persistence on the early 744A is very long.  For any kind of unstable or changing signal, you just ended up with a solid screen of colors.  Pretty, but not very useful.