Measuring Current with an Oscilloscope (Full Lecture)

ERROR at 30:40 Channel 2 has a peak to peak span of 6.4 divisions instead of 4.4 divisions. You should be obtaining the following values for channel 2: Vpp=64mV, Vp=32mV, Vrms=22.6mV, I=4.5mA/-81
This would also change the impedance calculations at 33:05: Z=1.2k/81, R=186.7, L=125mH.
In this lesson we'll examine an indirect means of measuring and displaying current on an oscilloscope by using a small sensing resistor in series with a load impedance under inspection. Using this technique a technician can simultaneously display voltage across and current through an element. Various properties including relative phase shift can be measured using this technique. (Full Lecture)
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[@bigbadtech]

ERROR at 30:40 Channel 2 has a peak to peak span of 6.4 divisions instead of 4.4 divisions. You should be obtaining the following values for channel 2: Vpp=64mV, Vp=32mV, Vrms=22.6mV, I=4.5mA/-81 This would also change the impedance calculations at 33:05: Z=1.2k/81, R=186.7, L=125mH.

[@melissafoxx4271]

I shocked myself when I managed to get the inductor value correct, it's amazing how much Ive learned about AC and DC thanks to ur lectures... Ive honestly never understood impedance really until I found u... So again ty for ur amazing work and time putting all this together... And thankfully Ive so many more lectures to go... man I freaking luv u xoxo

[@roseelectronics4582]

This was the most difficult lecture for me to understand thus far! I had to watch it quite a few times to get it nailed. It's partly because I don't own a scope and haven't used any in my life.

[@wileecoyoti]

This was extremely helpful, thank you!

[@eduinamaria8193]

This lecture just explained everything my teacher didn't. Thank you! Also, i measured the same circuit at different frequencies and got the same phase shift angle, why is that?

[@bigbadtech]

Good question. No matter what frequency you're running at a full cycle (ie: from 0 crossing going positive to the next 0 crossing going positive) always equals 360 so that proportional difference (ie: phase shift) will always be equal. Example 1: a 1ms lag for a waveform with a 20ms period is 1/20th of 360 or 18 degrees. Example 2: a 10ms lag for a waveform with a 200ms is also 1/20th of 360 or 18 degrees. Make sure you tell your classmates about these free resources!

[@eduinamaria8193]

@@bigbadtech thank you so much!

[@SiElect1207]

Hi Jim any discussion that tackles about RFI and EMI.??thanks for being so generous.Godbless

[@bigbadtech]

Not yet. As I get to more advanced material these would be worthy topics.

[@akdiscreto]

My thoughts on the example of the indirect current measurements using second channel on Rs. Though scope shows voltage drop over Rs on the second channel we see the voltage is leading total voltage drop by 90° though we measure voltage drop over active resistance.Thus the voltage drop on Rs channel is leading only because the current passing through the Rs is already shifted by 90° due to the capacitance.If the first resistance will be also active resistance,then we see no phase shift on Rs voltage drop when compared to total voltage drop.As there will be two active resistances in series, current over the resistances will be in phase with source voltage. That means,we can also find the current in series circuit having two active resistances using a scope. Can we hook channel 2 probes to measure voltage drop on the first resistance to find phase shift,rather than hooking channel 2 probes over Rs? We can knowing first resistance's value.

[@bigbadtech]

Yes, if you know the voltage across a resistor and the resistance value one would use Ohm's Law to determine the current magnitude. Current would indeed be in phase with the voltage across it. This works, however, the point of a 1 ohm sensing resistor is that the transfer function is stupidly easy (1A/V) and it works for pretty much any circuit even if the components are hardwired and can't be rearranged.

[@akdiscreto]

@@bigbadtech Thank You for the feedback.Good that You still follow the comments' rubric.

[@mrashad219]

Welcome to Pytel University of Indastrial Maintenance and Electrical Technology. Where you learn the stuff you are supposed to learn in the school you are paying for.

[@bigbadtech]

All for the low cost of zero dollars!