This time – a practical example, how important Memory depth is.

140M points vs 14K points.

Test example: Siglent SDS2000 series with a memory depth 140M points

Here, the initial signal. 14 seconds of data fit on the screen.

As you see, data are flowing in a continuous stream! We zoom the image for 10x:

We start to see separate data packages. Zoom in 10x more:

Zoom 10x more. We already have zoomed the initial image in 1000(!) times:

As you see, 2+ data packages fit on the screen.

On the memory of the oscilloscope, 1000 sets of such data packages are stored! But it is not all! Let’s zoom for 10 times more:

And 5 time more:

Here, in the memory of the oscilloscope, are 20’000+ of such packages! But nothing can deny us to zoom for 10 times more:

And again 5 times more:

At this moment, the image is zoomed for 2.5 million times!
At one go, the oscilloscope has stored 20’000+ data packages, and for each data package, each information unit – impulse – can be seen!
It took 14 seconds to store the data, but their analysis can take much more time. But with a guarantee – if there is any problem, we will find it!
And now, we will compare what the 14K memory depth is capable of. 14K is the smallest possible choice for the current oscilloscope.
Note: for the typical cheap oscilloscopes, the memory depth is even less: 1 .. 4K points.

Attempt No.1

We choose the initial time scale; it means 1 sec/div:

Where did the signal packages go? With such a memory depth, the sample rate is so low that the oscilloscope is not even capable of sampling the signal!
Let’s zoom for 10 times:

Yes, the situation is hopeless – no data packages are stored at all.
Let’s zoom for 10 times more:

Instead of data packages – separate pikes, which do not show the true result at all. Fail.

Attempt No.2
Reduce the requirements 100 times. Instead of 14 seconds, we will record 0.14 seconds.

Good news – signal packages can be seen! Let’s zoom 10 times again:

The signal of the packages looks with a very low resolution, but to make sure – zoom again 10 times:

There is no slightest doubt – the oscilloscope did not succeed in storing the package data! Fail.

Attempt No.3

Reduce the requirements for 10 times more to 1ms/div. Not the count of stored data packages is 1000(!) lower than in the case of 140M points:

Zoom for 10 times:

And 10 times more:

Excellent! Finally, we see at least one data package – the goal has been reached. Let’s see how much data the oscilloscope has stored. Compress the time for 2x:

Unfortunately, only one data package is stored in the memory of the oscilloscope. I remind you – in the case of 140M point buffer, more than 20’000+ data packages could be seen!

I think this example shows very well – memory depth has a crucial role in diagnostics! In real conditions (when the check-up of the signal with a very high frequency is not necessary), such a Siglent oscilloscope can record a huge amount of the data – minutes, even tens of minutes of continuous data flow. If the defect appears for at least one time, you will see it! In contrast, if the memory depth is 1..4..16K points, you will have to perform tens, hundreds, even thousands of tests, to find a sporadic defect.

Not even one data package is stored correctly! Fail!

The last attempt!
Choose the sample rate, so at least one data package could be seen correctly:

Excellent! Finally, we see at least one data package – the goal has been reached. Let’s see how much data the oscilloscope has stored. Compress the time for 2x:

Unfortunately, only one data package is stored in the memory of the oscilloscope. I remind you – in the case of 140M point buffer, more than 20’000+ data packages could be seen!

I think this example shows very well – memory depth has a crucial role in diagnostics! In real conditions (when the check-up of the signal with a very high frequency is not necessary), such a Siglent oscilloscope can record a huge amount of the data – minutes, even tens of minutes of continuous data flow. If the defect appears for at least one time, you will see it! In contrast, if the memory depth is 1..4..16K points, you will have to perform tens, hundreds, even thousands of tests, to find a sporadic defect