Sinewave in DC powersupply today in our physics class we talked about the hall-effect. Therefore we have used a Lab Quest with a sensor to measured the magnetic flux induced by a coil.
While adjusting the current to gather some values I noticed a steady lowering in amperage. And after replacing the power supply nothing happened.
Some time passed and I found an option to plot the data over time and the result was interesting. The graph showed an alternating wave-like relation, like a mixture of a sine and rectangular wave. It looked like a normal sine, but at its peek it stayed there for a full period doing a full leap and again staying...
I'm going to school in Germany and our ac power line frequency is about 50Hz and the wave had an duration of about 50 seconds and i can imagine there could be a relation.
So my question is now what could possibly generate such an effect? and therefore wich device is broken?
 A: DieKautz, there is at least one issue with your data.  Your AC current is 50 Hz.  That means that there is one positive peak and one negative peak per cycle.  Assuming that you want to plot an accurate representation of these cycles, you need to sample the signal at a frequency that is at least twice as fast as what you want to plot.  Since a positive (or negative) peak occurs over a time frame of 1/100 of a second, you need to sample the signal at a frequency of 200 Hz or higher, and the higher the better.
I've used a Lab Quest in my high school physics labs while teaching students.  I know that the sampling frequency can be adjusted, but I don't remember the fastest setting.  Check the device, and attempt to sample at the fastest possible rate.  If you can't sample at 200 Hz or higher, you will not get good data.
If you sample at too low of a sample rate, you will run into a problem known as aliasing, which you commonly see when auto commercials show a car's wheels spinning "backwards" as it travels down the road.  If this is occurring, the signal you see will not be a true representation of what is happening.  For more info on aliasing, see https://en.wikipedia.org/wiki/Aliasing
