How to use the VI oscilloscope on an externally powered supply?

[Wes_Plybon]

I am not getting the expected signals when I use the VI oscilloscope to test a power supply circuit that has an external transformer connected to an AC outlet.  I suspect the VI oscilloscope is using a different ground reference.  How do I connect the VI oscilloscope ground reference to the ground in my circuit.  Connecting the scope probe ground did not work, nor connecting the circuit ground to a power supply ground on the ELVIS station.

Thanks

[Sputnikrent]

Hi Wes,

1) Could you describe what your current setup is like? Are you using ELVIS or ELVIS II? 

2) What are you expecting to see, and what are you actually seeing?

3) Have you tried using a regular DC source (e.g. a battery, or 12V bench supply) to check and see if the connections are set up fine?

[Wes_Plybon]

As far as I know it is just a regular ELVIS station.  I have a transformer connected to a 110V AC outlet with a full bridge, filter caps, and a 1K ohm load.  I need to measure the DC level and ripple on the output.  With an external scope I am able to do both.  With the VI scope I get a sine wave that is clamped to 0V when it is less than .5V.  The reason I started using an external scope is because I suspected a grounding problem.

I read later that someone was having a similar problem with an analog channel and someone suggested to connect the AIGND to the circuit ground.  I have not tried that yet.  Thanks for your reply.

[Sputnikrent]

Hi Wes,

Yeah try doing that, it might be a good direction to start investigating. Let me know how that goes!