Switching the probe points doesn't invert the tension?

Instruments PC Oscilloscopes and Recorders
1

Hi,

I recently bought a PCSGU250 oscilloscope and am quite new to electronics, so my bad if this question seems silly.
During some testing I discovered that in some situations, inverting the probe points (measuring between A and B and than measuring between B and A) didn’t give the opposite tension…

It occurred when I generated an oscillating tension Vpp = 5V with an offset of 4V. In the first configuration where the “ground” probes matched, I got the right observation on my CH1. But when I inverted the CH1 probe points, my signal is a 0V constant tension.
I realized it actually occurs with every oscillating tension.
I used to work with some other oscilloscopes and I have no memory of this particularity.

I suppose I am doing something wrong, and probably the “ground” probe of CH1 is supposed to be connected to a DC tension.

Can somebody please explain me what I’m doing wrong ? And is there a way to make this oscilloscope work “in both ways” ?

Thanks a lot and have a nice day.

2

Not a silly question.
There is only implicitly informed in the Help file that all the instrument grounds are interconnected.

[quote]In the first configuration where the “ground” probes matched, I got the right observation on my CH1. But when I inverted the CH1 probe points, my signal is a 0V constant tension.[/quote]Yes, if you connect the ground lead to the function generator output, you’ll short circuit the function generator output to ground. This is why you get 0V.

3

[quote=“Thomasss”]
Can somebody please explain me what I’m doing wrong ? [/quote]

Take EXTREME care wher you connect the Ground clamps of the probes!
If you put GND to some higher voltage level in the circuit and have and USB connection for example
you may BLOW UP! AND I MEAN BLOW! LIKE EXPLODE! YOUR PROBES!

Look here :

youtube.com/watch?v=xaELqAo4kkQ