Swend
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As a service for the persons reading this post, I made the following calculations:
Please explain: if you are using R(t)=U(t)/I(t) to calculate the resistance, I have no problem.
But the 4th graph is misleading, because you are trying to plot a point where the R becomes infinite.
Such points are singular and must be skipped in the plot. That happens when you have a finite U(t) but the current I(t) becomes zero, you have this problem.
if the U(t) or I(t) are not constants in time, they must be treated as a complex quantity. Then R(t) is also complex and has a real and imaginary parts. At the singular point, the real and imaginary parts are equal and opposite.
Yes that's how it's calculated.
Yes, I agree in the case of singular points, but 6.7e10 as in the plot is still finite.
And what if both U(t) AND I(t), as the case is here, are not constants in time?
What you have done is called point-wise division. This may not be same R(t)=U(t)/I(t) under some conditions. Particularly near singularities. I won't go into these details. Recall that division by zero is not defined.
You must know the waveform: in other words, the voltage a moment back has an effect on the current at the present moment (if your circuit is reactive). Because of Ohm's law, only two of the three (U,I and R) are independent.
Simple questions do not have simple answers. I will stop here.
The calculations and respective conclusions are presuming correct I and U measurements.
Particularly the current measurement is very implausible, see previous discussion, e.g. post #12.
I agree with KlausST that the current measurement channel seems to be inverted. I' d think about possible alternative explanations if I see the pulse response form the start.
Yes, but in this data series, the current is never zero, otherwise the calculating script throws a divide by zero warning, which it doesn't in this case. - so no zeros.
As I have said several times, and as it can be seen in the trace, before the pulse - both current and voltage are zero. And the pulse in the trace is the very first after power on
I gave some hints why the current waveform is likely to be distorted by the characteristic of the transducer. There may be more problems with your circuit that are not so obvious at first sight.
In my view, the final prove that voltage and current waveforms are not consistent is the apparent "resistance" you have calculated. At this point, it's pretty clear that the measurement function needs to be validated from the very bottom.
when both current and voltage are zero, what is the calculated value of the resistance?
Hint: all physical measurements take time and all the results are simple averages over the measurement time period.
How can a single point in time measurement be an average?
Then you have a serious singularity problem.
You need to use l'Hospital rule to get R(t=0)=a/b
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