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Rigol DS1052E - Nasty bug

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sgpee:
Guys,

I bought a DS1052E. This is with stock firmware 2.04. The bloody scope doesn't work well with 1msec time scale. In 1msec, it sometimes shows signals that has a 5usec period as 5msec, there are several other similar problems in that range. When you move to 20msec or go down to 50usec level, things are all dandy.

Anybody run into these problems? I upgraded to 100Mhz, still the same, I guess, there is a fundamental issue in the firmware.

Thx, SGPee..

amspire:
I think you are just seeing aliasing problems which is always a potential problem with Digital Oscilloscopes.

Here is the situation. At 1msec per division, the scope is probably doing 200 samples per division.

That is one sample per cycle of your 200Khz waveform.  How can you properly show a waveform accurately with one sample per cycle?

Now we can also deduce the exact frequency of the applied waveform.

If you are showing a 5mS waveform, your applied signal is something like 0.1% off 200KHz according to the Rigol timebase. So I assume the Rigol sees the applied waveform as 199.9kHz or 200.1 kHz.

Checking for aliasing is just something you have to check for with a  digital oscilloscope, and if you used an analog oscilloscope, you just don't have this problem at all.

If you turn on long memory in the Aquire menu, the Rigol can increase the number of samples, so there are now many samples per cycle, and it will work the way you expected.

So it is not a bug. It is the oscilloscope working exactly as designed. What you will find is if you press the "Auto" button, the oscilloscope will probably switch to the correct timebase to see the waveform properly, so use Auto to check that you are not confusing yourself by looking at a fictitious aliased waveform.  Once you learn this, you will have no problems.

Richard

Fender123:
Another option is to enable Peak Detect from the Acquire menu.

amspire:

--- Quote from: Fender123 on August 18, 2011, 01:14:28 pm ---Another option is to enable Peak Detect from the Acquire menu.

--- End quote ---

Thanks. I didn't know enough about the DS1052E to work out exactly how the peak detect works, but I guess if it is recording a sample every 5 usecs, it is actually measuring over that 5 usec at maximum sample rate (ie 5000 samples in single channel mode)  and it records the maximum and minimum values. Does that sound right?

If that is so, then the Peak Detector is a very reliable way of avoiding aliasing. That is excellent.

The scope probably isn't going to be left in Peak Mode all the time, so it is up to the operator to be aware that Aliasing can happen and to check for it. The means of checking can include going to faster time bases, enabling the long memory, using the Peak Detector and by pressing the Auto button to see what the scope thinks.

Or have an analog oscilloscope handy to double check the signal.  If it is a repetitive signal, the analog oscilloscope will give a more detailed waveform anyway.

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