If the scope has a 300V Cat II rating, does this mean I can meausre mains voltage which could be 340V Pk-Pk?
The isolation rating means that there can be 300V RMS (or DC) between the ground clip and the PC’s ground (and for safety considerations this applies to the probe tip too). But the USBscope50, with a x10 probe, can measure up to +/-300V i.e. peak-peak this is 600V. The scope itself will be easily capable of measuring the 240V RMS level because this equates to about 340V pk-pk, and the scope can handle 600V pk-pk. Also remember that the x10 probe includes a 9MegOhm resistance, which works with the scope’s 1MegOhm input resistance to attenuate the signal by a factor of 10. So the 240V RMS signal on the probe tip turns into a 24V RMS signal at the scope’s input. The 300V Cat II rating really can be thought of as the maximum voltage that can be tolerated between the ground clip and the ground of the PC that you are using i.e. the allowable difference in potential between the unit under test and your PC. It’s not directly to do with the measurement range of the USBscope50. So the answer to
