Body
Hi Sven,
Try to have only one single earth point in any circuit.
If you are using a 2 channel scope the earth clips on both the the probes
are connected together. inside the scope so we are unknowingly shorting the
2 earth clip points together.
Also often our scopes are earthed back to the ac mains supply, so where we
place our earth clips creates an actual earth at that point.
So have the current shunt in the low earthy side of generator source and
clip the scope probe earth clip there at that single earth point.
Leave the earth clip off the voltage measuring probe altogether, just leave
it free ...unconnected, or connect it back to same point as the current
probes earth point.
When doing your Volts and Amps calculations just remember to subtract the
current shunt voltage from the applied voltage measurement.
As this voltage drop across the shunt is lost to the circuit under test so
the circuit "sees" the generator applied voltage minus the current shunt
voltage.
If you really need to make a differential measurement between 2 points with
an analog 2 channel scope, you can hook both probes to either side of say a
shunt resistor.
Select Channels A+B on the scope and invert one Channel, but to get
accurate readings both channel gains need to be identical and both Y
Volts/div settings have to be the same on both channels.
Or can use battery powered scope where whole scope and earth clip can float
above earth potential.
Just be aware of Danger from body of scope at high potential if applicable
and stray effects at higher frequencies & impedances.
Gerry
On Sun, Dec 17, 2017 at 2:57 AM, [email protected] [EVGRAY] <
[email protected]> wrote:
>
>
>
> Hello Ole, people,
>
> I have problems with my new scope.
>
> I wanted to measure the current at a current shunt 50mV per ampere, so I
> connected the probe to both contacts and wanted to measure the differential
> voltage. Unfortunately I have earth connection now. The energy flows
> through the scope. It is not measurable. With the Velleman in battery
> operation I could look at the sine nicely. What am I doing wrong?
>
> I wanted to measure the voltage curve and current curve simultaneously in
> the reactive circuit.
>
> regards
>
> Sven
>
>
>
>
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>