C calibration problems

Hello everyone, my dso quad arrived yesterday and I immediately upgraded the firmware and began to calibrate the probes using a very vague guide I found. I was able to get a near perfect square wave at the suggested 10kHz and 50us. However, at this calibration, my sine wave (from the built in generator) is filled with “steps” shown in the attached image. If I then calibrated again to make the sine wave smooth, the square wave becomes horribly distorted. This problem occurs even in the Hz range and I can’t seem to find a reasonable middle ground.


If you have “calibrated” the probes on the adjustable capacitors underneath the battery for a nearly perfect square wave, then it is OK! It is actually called “probe compensation” and is made to achieve a more linear frequency response, resulting in steep edges without under-/overshoot on a square wave. Actual “calibration” of the DC voltage levels is done in software by another procedure.

The sine output has steps because the scope makes it so. The sine is generated by software via a D/A converter - and apparently the software is too slow to make it smooth. If you are smoothing the slopes with the probe compensation it is because you are reducing the frequency range of the scope - resulting in a low-pass filtering of the signal.

BTW. where did you find the guide for this? (I did it myself by experimenting…)

Thanks for clearing that up!

I found the guide in the thread “DSOQuadV2.6 RESOURCE(Update 2011/7/22)” in this section which has a PDF file called “How to adjust the C to calibrate the probes.pdf”.

Now if only I could get the automatic calibration to work, I can’t even get it to show 0V when I have the probe connected directly to ground!