#855

[@vincei4252]

With the usual reminder that the ground lead needs to go to ground unless the scope is isolated from the thing being measured. This is for those that have the Eureka! moment and think why can't you just put the leads across the component :-)

[@TonyBarr99]

Thank you Vince! You read my mind.

[@robertmontgomery3892]

@@TonyBarr99 Ditto

[@BradKwfc]

Dont BLOW your scope brah!

[@davidahmad6090]

Here it seems he is using the two voltage probes in a sort of diferencial Mode, so it is my beleif that there is no need to connect the ground probes at all, just the probe tips. Also i thought this method only works when the resistor is on the low side of the circuit, i.e. one side of the resistor Connected to ground?

[@ruhnet]

Fantastic---what a helpful use of the simple A-B function!

[@MsStrej]

Wow, it’s so obvious yet I wouldn’t thought of it without your video, thanks!

[@alocin110]

Excellent demonstration of an intelligent technique. Thank you for sharing. I liked your video.

[@shawncalderon4950]

An excellent presentation!

[@fiorenzo6301]

How did you get thin traces like this? Because on my oscilloscope, the same rigol mso5000 you have, them are thick and full of noise. Without avaraging i cannot get the same visual result as you but you don't seem to use avaraging. Thanks

[@IMSAIGuy]

I don't remember on this video. The scope is very fast so it shows lots of noise on traces. I also use averaging a lot and reduce the BW to 20MHz depending on what I am doing. Good grounding helps of course.

[@BrendaEM]

Thank you for the video. Recently, I found a gotcha, in that I was trying to use my function generator output to pick off the voltage across a resistor to sense the current for the Y axis to trace a transistor curve, but I couldn't because both instrument BNCs are grounded. My first clue: it picked off the voltage without the ground lead attached. This is why--even an old isolated, low voltage transformer works as the lowest form of curve tracer, yet my function generator would not work that that (re)purpose. While I am not optimist that the 1054z would accept the output of a math function as y-axis component of the XY, this video was food for though. Thank you for the video. It's iconic that the old scopes had a built-in trace function, but a modern digital scope doesn't. : P An isolation transformer would have fixed this problem, but some people do die from 115v AC, and well, the BNC jack is indeed metal and well the switcher has 90vDC in it, which I likely would hold onto for the rest of my short life. Still, I hate the specter blowing up my equipment because grounds are connected. There are curve tracer kits, but I am on a very limited budget.

[@nithinks4047]

What should be the value of resistor to sense the current perfectly....

[@avi-brown]

Thanks for this! I am interested in measuring the current draw of an entire circuit (battery powered) over a few seconds. Could I treat the entire circuit as the "resistor" (load), connect probes to the + and - of the battery, subtract the 2nd signal, and then convert to amps by dividing the voltage by the circuit's equivalent resistance (assuming it is constant over sleep / active cycles, which I need to check)? Or maybe I should introduce a very small (shunt?) resistor in series with the + or - terminal the battery and measure across that resistor in parallel...?

[@IMSAIGuy]

no, you would be measuring across the battery in parallel with the circuit. you need to have a resistor in series

[@avi-brown]

@@IMSAIGuy Thanks. So a resistor in series with, say, the positive terminal would work? Any recommendations for going about deciding what size resistor to use?

[@IMSAIGuy]

@@avi-brown kzbin.info/www/bejne/mXfGqHuMpdWoadk

[@IMSAIGuy]

pick a resistor that allows a good measurement and can handle the current. be wary of the burden voltage.

[@avi-brown]

@@IMSAIGuy Thanks so much.

[@BenFreemanDC]

Did yo someone input the value of the resistor into the Oscope? I still don't see how you can get the current measurement from those 2 probes. i understand from the probes you get Va-Vb = Vab but then Ohm's law says you still need the resistor value to get the current.

[@IMSAIGuy]

you need to read the resistor color code or look at a schematic for that.

[@RicardoPenders]

Cool, thanks for sharing... This is a very useful video.

[@davidahmad6090]

Great video sir, i am wondering if you connected the ground clips, logic tells me you did not, becuase you are using both volage probes in a sort of differential configuration. Can you use this method on a resisor at any location in the circuit or is it just on a low side resistor, with on side connected to ground ?

[@IMSAIGuy]

I think it best to connect the grounds. you can use resistors on the high side as well

[@davidahmad6090]

@@IMSAIGuy Very interesting, thank you sir.

[@iliakotliar7723]

If I use differential probe: do I get same results ?

[@IMSAIGuy]

yes. most diff probes are for high voltage, so you will have problems at low levels. low voltage diff probes are quite expensive

[@EfieldHfield_377]

Poor man diff probe is A - B. Two things i could never bring myself to buy for my lab, A diif probe and a good current probe. The current probe more than anything is what I miss, not greedy if i had something up to 10MHz, but alas i have a cheap bk 300kHz probe, and a sense resistor every now and then. Some day i will buy that probe. Thx for sharing.

[@waterfuel]

Is 6 amps AVERAGE DC current on hand held multi-meter, or panel meter,, the same as PEAK 6 DC amps on oscilloscope? I thought it was a 60% difference.

[@IMSAIGuy]

DC is constant voltage/current. there should be no difference between average and peak unless there is a lot of noise on the DC. then the peak would be a very small amount more.

[@ammarbasrah1362]

Show this connected plz

[@rajaqamar06]

Question: Patch a RC circuit and connect it to AC input voltage source. DIsplay the voltage waveform of capacitor voltage and waveform of capacitor current simultaneously without using MATH mode of the oscilloscope. Use oscilloscope only to get the desired result.

[@dohack]

this is with square wave as input from function generator. What if want to measure current drawn by a MCU or BLE chip like STm32wb55rg powered by battery. I don't have Power Profiler. Just an oscilloscope 100 MHz 4 channel and multimeter. I want to measure 200nA to 1A current measurement range. any tip or IC suggestion ?

[@TalpaDK]

One tip... Get the nRF power profiler

[@niknam.]

that's right ONLY if you know the resistors true resistance! but if you not?

[@IMSAIGuy]

Then it's a more difficult day

[@giostechnologygiovannyv.ri489]

what if the circuit is an op amp made up out of many MOSFET's and no resistor to measure? ^^''

[@IMSAIGuy]

you will need to unsolder parts of the circuit. 1. use current meter 2. use clamp on probe 3. add a low ohm resistor and do as per video. 4. there are very expensive probes that I have never used that can detect current in traces.

[@giostechnologygiovannyv.ri489]

@@IMSAIGuy Thanks for the answer!! :D

[@mu8502]

hi can I use 150 MHz probe on 50MHz oscilloscope?

[@wilburnurbil9848]

It depends, but probably. Try it. If it adjusts properly when using your scope probe adjustment square wave then you're go to go. If the input capacitance of the scope falls within the adjustment range of the probe then you should be fine. Example, Tektronix 2225 50MHz scope has an input capacitance specified at 25pF, plus or minus a couple pF. A Tektronix P6130 probe has a -3db bandwidth of between 150 - 250MHz depending on probe cable length. The probe specification says it will be happy with scopes between 10 to 30 or 35 pF, again depending on cable length, so should work well. The 350MHz probe that comes with the Rigol MSO5000 series scopes is specified to handle scope inputs of between 10 and 25pF. It might not adjust properly to the Tek 2225 where it's right at the limit. The Rigol probe should be fine with a Tektronix 2215A (for example) which has a 20pF input capacitance and a 60MHz bandwidth.

[@peterjohnson5586]

Resistors have +/- tolerances.

[@jj74qformerlyjailbreak3]

My old scope has Analog add function. No subtract but what can I say, it’s from the late 60s.

[@IMSAIGuy]

no problem, you had to just invert one channed

[@jj74qformerlyjailbreak3]

@@IMSAIGuy I was thinking that but my channel 2 is out so I couldn’t test my thinking at the time. Thanks for confirmation Great channel.

[@sammin5764]

🌷

[@ColdWarVet607]

Respectfully I'm not following this. By introducing a capacitor the circuit has another load, another path to gnd, thus more current will flow than if the capacitor was not there. When the waveform is "low" the capacitor is discharged and thus a short to gnd. As the waveform rises max current flow occurs as again the capacitor is shorted to gnd. With the new path to gnd o the shorted capacitor, the rising math waveform representing current is initially limited only by the series ESR and Self Inductance of the capacitor. That is the peak we see on the math waveform. Then of course as the capacitor charges its reactance limits the current flow to gnd and we see the typical soft landing curve. So what Im seeing on the waveform is the current through the added capacitor not the current that would be flowing into a high impedance ckt like an op amp or just through some 1K resistors to gnd which should be significantly different. Okay....please explain to me where Im going wrong here. Thanks! Nice to the point video, thanks for that too!

[@jdmccorful]

If you have the correct scope?

[@mavamQ]

I think most scopes will do A + B. To get A - B, you need to invert B. (I think, I haven't used the function for a while)

[@vincei4252]

@@mavamQ Yeah, a lot of scopes have an invert and add function. My old tek 2465B has this. There's no "math" since the 'calculations' are done in the analog domain.

[@jdmccorful]

Thanks for the info.

[@vincei4252]

@@jdmccorful np

[@frankowalker4662]

My digital scope dose'nt have any maths functions. LOL.