Did you ever tried to insert the terminals (voltmeter) in a way parallel to magnetic field lines? Just moving the angle should change the voltage IF this is a probe induction problem.
It appears, that the very tip of the probe and it's position is creating the tension. It varies (+- a bit) when you change the angle. In case we are doing that set-up again, we could show that.
Did you ever tried to insert the terminals (voltmeter) in a way parallel to magnetic field lines? Just moving the angle should change the voltage IF this is a probe induction problem.
It appears, that the very tip of the probe and it's position is creating the tension. It varies (+- a bit) when you change the angle. In case we are doing that set-up again, we could show that.
How about using salt water or mercury to connect outer rims? Lesser friction isn't it?
This would be something to try for a commercial unit - after we have figured out how exactly the current is created.