Oscilloscopes with good time base update speed?

[assafa]

Hi all,
I'm looking for a low budget scope – with a good refresh rate at relative high time base settings.
I need to measure frequencies that can go well beneath 1Hz.
Until now I was pleased with the TDS1002B – that works much smoother then a
modern RIGOL DS1204B, so I'm quite puzzled about what I can get with the new cheapo digital scopes.
I'm thinking about a budget in the range of 300-400US$
(I prefer a digital scope because of the size)
So if anyone has a good experience with a particular model, I would be happy to know about it.
(BTW – I don't mind getting another used TDS1002B – if you think he would do better than a new cheapo one - at the same price)

Assaf

[David Hess]

Do you mean slow or fast timebase settings?

At slow timebase settings, acquisition rate is dominated by the time taken to fill the acquisition record.  The only real control over this is to make sure the acquisition record is the same size as the display record.

[KedasProbe]

Did you consider an USB scope that can continuously measure in streaming mode? (relatively low sample rate)

[assafa]

Thank you guys for the replays
What is mean is that if I try to use 50ms, 100ms or higher settings, I don’t get a real time
display of the signal, there is a large delay (latency) or a “stuttering” display of the wave form.
I’ve also tried a PC based scope (using a parallel port) but it won’t go anywhere above 100ms, and starts to fail even at 10ms.
If any of you guys have RIGOL/SIGLENT/OWON – or any of these cheapo scopes, I’m appreciate it if you could check the 250ms and above (time base scale) and let me know how they behave.
Thanks,

Assaf

[tautech]

Most DSO's at low timebase settings(~10mS or slower) depart from a continuous sweep state to an Arm/Trigger state.
This can normally be seen with the Trigger state indicator on screen.
The steadiness of this state will depend on the signal and the Trigger setting.

One can normally find the result needed with a Single trigger setting and other Trigger settings at slow timebase settings.
I often use this method for checking slow digital signals.

Edit
Thanks David  Roll mode

[David Hess]

The latency and low display rate are just an artifact of not displaying the current acquisition record until it is filled.

The DSO I normally use supports roll mode at timebase settings of 100ms/div and slower so the strip chart like display has no latency.

[w2aew]

If your scope doesn't have roll mode, and if you don't need the display to be triggered (stable with respect to a triggerable feature of the signal), then you might try changing the trigger to "Line" so that it triggers often enough to keep the trace somewhat live.

[assafa]

Thanks again guys.
I don't think the trigger settings is the issue here.
In my understanding, the problem is the amount of data that needs to be displayed and processed when using low time base setting.
Unless there is a strong processor and a very big buffer, you must change (lower) the sampling rate at low time base settings.
Since the TDS1002B is relatively old, I guess that he has this (changing the sampling rate) feature, and the new ones – being much faster - rely on process power.

Maybe I should be looking for a low bandwidth scope…

[rob77]

just tested my Hantek DSO1102B - with long memory (2x512K) and 400ms timebase in triggered mode with 2 channels enabled - not a problem. but with 800ms timebase it's running in scan mode only.
with short memory (4K) it goes to scan mode at 80ms timebase.
timebase can be set to 2Ks (yes 2000 seconds) at 10samples per second , but haven't tested that one obviously (it would take 8 hours to capture and draw the waveform across the screen )

[assafa]

just tested my Hantek DSO1102B - with long memory (2x512K) and 400ms timebase in triggered mode with 2 channels enabled - not a problem. but with 800ms timebase it's running in scan mode only.
with short memory (4K) it goes to scan mode at 80ms timebase.
timebase can be set to 2Ks (yes 2000 seconds) at 10samples per second , but haven't tested that one obviously (it would take 8 hours to capture and draw the waveform across the screen )

Thanks Rob! 

[jaxbird]

Just tested my Owon. At 100ms/div and above it goes into rolling scan mode. Max timebase is 100s/div.

It's got a fairly large 2x10Meg memory so the sample rate at 100ms is 5MSPS and at 100s it's down to 5kSPS.

[assafa]

Just tested my Owon. At 100ms/div and above it goes into rolling scan mode. Max timebase is 100s/div.

It's got a fairly large 2x10Meg memory so the sample rate at 100ms is 5MSPS and at 100s it's down to 5kSPS.

Thanks jaxbird :-)