Electronics > Beginners
Memory Depth - scope
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Bandoneon:
Hello everybody,

I want to measure the memory depth of my scope, is there a possibility to do this? I use a Rigol DS1062CA and I want to do this because I want to check that the manufacturer of the scope is right and if I change the inputsignal I want to look that the memory depth is still the same.

I found already this formule on the internet, is this formule right?
Memory depth = Sampling rate * time per division * #divisions

Who can help me?

Greetz
ArthurDent:
I'm not sure you are looking for the right variable. Memory depth for any given scope is given in the specifications and for any trace is divided by the number of channels you have turned on. To maximize memory depth, use one channel if possible. Selecting the highest time/division will help also. The formula is (Memory depth/time per division) x number of divisions = sample rate.  https://www.testandmeasurementtips.com/memory-depth-and-sampling-rate-in-oscilloscopes/

Here is a good explanation: http://literature.cdn.keysight.com/litweb/pdf/5989-4501EN.pdf
ataradov:
Why would manufacturer lie about this stuff? Especially given that specified value is just 10 kpts. It can't go any lower, really.
w2aew:
Not all scopes share the memory among channels.  In other words, some scopes give you the same maximum available record length regardless of how many channels you have turned on. 

Also remember that the displays on digital scopes rarely have anything more than 1000-2000 pixels across the screen horizontally.  So, even if you capture a waveform using 1Mpoints - depending upon how to view that waveform (zooming in/out, or making measurements, or exporting the waveform for external analysis), the number of points in the waveform may be different that the memory specified for the acquisition.

Some scopes give you direct control over how much memory is being used, and will report this value to you somewhere in the user interface.  Some scopes don't tell you easily.

Also note that some scopes use a decimated set of display point for the on-screen measurements, and some use the acquired samples points in memory - this can fool you sometimes too.

Bottom line, you have to take care in how you use the scope to determine the amount of memory used, and how to control it.
David Hess:

--- Quote from: ataradov on March 08, 2019, 07:50:20 pm ---Why would manufacturer lie about this stuff? Especially given that specified value is just 10 kpts. It can't go any lower, really.
--- End quote ---

Some manufacturers have lied about or at least misrepresented record lengths as they are a major marketing feature.  The instance I am thinking of involved the manufacturer listing the number of *bytes* of record length but with 16 bit samples, this number was twice as high as the number of samples.
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