Is it possible to measure current that is flowing for 2 or 3 milliseconds inside a circuit through oscilloscope by measuring the voltage drop across a resistor ?
The supply voltage is generated by triboelectricity and it has a peak to peak of around 5 volts, it lasts only for about 3 to 7 milliseconds. I have connected this to two resistors in series, (10 Ohm, 10 Ohm) and i measure the open circuit voltage that is generated by triboelectric impact and the voltage drop across the first resistor to find the current in the circuit. So they are connected to two channels in oscilloscope (Voltage probe, 1x attenuation, probes are compensated)
But, it turns out that i see nothing in the oscilloscope, i cannot measure the the tribo electric voltage as well the voltage drop across first resistor.
When the two resistances are very high, say 100 Kilo Ohms, i see that both the channels in oscilloscope show the same open circuit voltage that is generated by triboelectricity during impact. How can i measure current ?
Best Answer
It sounds like you are inadvertently shorting out the resistor you hope to measure current through because the scope probes have a common earth point. If you have one scope probe's earth crocodile clip on the bottom of the lower resistor you can't arbitrarily connect the other probe's earth clip to a different point in the circuit because it shorts the two nodes together.
Take a step back and think what you are trying to do. If you connect one resistor (10 ohm) to your triboelectric generator and measure the voltage across this one resistor you can perfectly assume that the current through that resistor look exactly like the voltage across it.
This is basic ohms law i.e. I = V/R - if R is a constant then I is proportional to V and will be identical to it other than scale.
If it so happens that you see no voltage across the ten ohm resistor this is because your scope isn't sensitive enough. In which case, increase the resistor value or use a scope preamp.