Easy DIY passive
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- Опубліковано 7 лют 2023
- Do you have to measure mains voltage waveform just once in your whole life? Differential probes are too expensive? Here it is a simple, cheap, DIY solution.
CAUTION: Working on mains voltage is dangerous, you MUST know what you do.
Directly using the probes of the oscilloscope to measure the mains is hazardous, it could lead to from destroying your probes to melting the traces of the PCB inside your oscilloscope, not to mention the risk of being injured. Depending by the grid system you may have 50% to 100% chance of causing a short capable to destroy your instrumentation.
In an old video I presented a depth analysis of why you can blow up your oscilloscope while making measurements at mains, follow this link: • Correct use of the osc...
Also the trick that uses two probes directly may end up in catastrophic results if you work on voltages above 110V RMS.
In this video is presented a simple attenuator made of just 1/4W resistors, that guarantees safe operations with the oscilloscope provided the PE (Protective Earth, the yellow-green/green wire) is actually tied to ground. It still requires two input channels of your oscilloscope but it is safer than directly hooking the probes to the mains.
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Great job, thank you for clarifying a very needed topic.
For long time Im looking for this circuit
Thanks ❤
Thank you for your video.
Well Done !!!
Thank you, good job!
Glad it was helpful!
Thank you, i was always afraid to connect my scope to mains.I know what will happen, but I was nor sure way.
If you just want to look at the 50 or 60Hz sine wave of your mains outlet with your scope, you don't need anything extra to build.
Mains outlet is referenced to ground / protective earth, your scope probe tip is also referenced to ground, so you don't need to connect your scope ground clip to the neutral of the mains. Just set your scope probe at X10, remove the groundclip and touch the Hot / Line / Phase of your mains outlet, and you will be fine without doing damage,
or tripping RCD. Also, if you have 2 x10 scope propes, you don't have to build any extra. Just set each probe at x10, connect both groundclips together, set your scope to measure differental by choosing channel B ADD to channel A, and set one channel reverted. You can then use one probe tip to touch Hot / Line / Phase and the other probe tip to neutral. Both groundclips are only connected to eachother, not to anything else.
Before i got a differential probe, i used method 1, by using 1 x10 probe and no ground clip. If you want to do measurings in circuits that are powered by mains, then method 1 is not advised. Grtz from Belgium
Please watch the video where I talk about this topic. Neutral is normally connected to PE but it is not guaranteed it's at the same potential, and this is especially true when it comes to diagnosing. Method 1 is dangerous because voltage is above the rated voltage of many probes and scopes. Method 2 uses two channels. Also with method 1 you wouldn't be able to measure in-between voltages in a circuit, for example across a resistor that is not referenced to neutral. Finally even with method 2 you are at risk with common 300v probes, even though in practice it should be unlikeable that it breaks down with just 25v above its rated voltage.
Greetings from the Alps.
@@AccidentalScience , X10 probes have only 1/10 of the input voltage on the output to the scope. If you are measuring 240V, the output to the scope is only 24V.
The cheapest scope probe will measure up to 600V, but take that with a grain of salt and say 500V, that means that only 50V is going to your scope.
Each channel of your scope can measure up to 300V directly, so you have safety range of 250V, when measuring 500V with a X10 probe.
The only problem that occurs when measuring 500V with a X10 probe, that your measuring on the screen will be out of range, so a X100 probe is more suitable when measuring above 250a300V AC.
Also with the DIY passive probe, your readings are not correct.
If you are measuring mains voltage, what is referenced to PE, one side of your voltage divider is bypassed for 50% because each end is connected to PE, the result is that when you measure a floating voltage, this voltage divider is not bypassed for 50% , so the voltage to the scope is 50% lower.
If you choose for a X100 attentuation, and you measure 240V AC PE referenced, 2,4V is going to your scope, but when you measure 240V DC or 240V AC not PE referenced, only 1,2V is going to your scope.
@@BjornV78 dude, insulation is determined at each level of the chain! A 300V probe has insulation in respect to GND that is carried along its cable up to the tip and around the internal resistor and capacitor. They are rated to withstand a given voltage in respect to GND. Also while in the eightees 600V probes were common, nowadays it seems that is no longer the case, sadly.
About that thing that with the passive probe you would read 50% of the voltage, well it is plainly wrong. Look at it better. Remember that you are using two channels linked with math differential. Also think at the case you need to make a measurement that is not referenced to PE, but still the circuit is referenced to PE.
@@AccidentalScience , may i mail you the drawing of what i mean by the 50% misreading ? A picture says more then 1000 words :-) Grtz
@@BjornV78 sure, my mail is in the about section of the channel.
No capacitors for frequency compensation? I wander what's the bandwidth of this differential probe. I guess not huge.
Yes, I forgot to mention it in the video. BW should be about 20KHz which is acceptable for reading very low frequencies. It is a trade-off between performance and simplicity+safety. Adding compensation would have required a series of good, high voltage capacitors, making the whole thing bulkier for a dirty quick simple solution. After all 20KHz is generally enough for things that work at 50/60Hz. So I choose to add the compensation to the active probe that will be shown in the next video.
Thanks for your comment.
I wonder what to do in the situation faced by me?
The two Neutrals from the two outputs 230 VAC of the Nitrox Inverter ( 3 KW - 24 V, SP - Hybrid _ by A.P.T. ) aren't allowed to be jointed! At my home the PE and the Neutral are NOT jointed! Neither the Solar Panels nor the Inverter is Grounded till now! The Inverter demands the two Neutrals to be isolated and afloat! I'm rather perplexed. Obviously the two Phases are certainly to be distributed isolated!
The problem faced has been that either regular Load RCD or the Smart Load RCD have been in the habit of tripping off upon Grid On / Off since installation. Even sometimes the RCD on the Input to the Inverter also goes off!
The reason: the wiring of my home has become leaky for sometimes. I've been curious about the Phase difference of the two outputs of the Inverter. Is there any way to examine it's two lines 230 VAC (RMS) each. Probably phase difference of 120° with about 460 VAC (RMS) that amounts to be ~ 651 VAC RMS, oh no, sorry I mean to say 650 VAC Peak ! Moreover, the grounding croc clips of the O-Scope share the same common ground!
Is there any way to compare the 2 outputs, one 'Regular Load' and the other 'Smart Load' be visualized on single O-Scope screen with custom devised High Voltage Probe(s) X100 on single or Dual Channel OScope?
Note: The Inverter trips the RCD's on bringing the the neutrals near each other. I've a plan to examine the phase relationship of the Regular and the Smart Output phases without putting any load on these.
The OScope to be used is a Rechargable Battery Operated ( Floating ) DSO ’ZEEVEII DSO3D12’
I've seen your kind vlog on a ’DP’ Passive Differential Probe utilizing Dual Channels on an Oscilloscope for measuring High Voltage safely, safe for the Operator, the OScope and the Device Under Test DUT.
Would you suggest me to use similar probe for the situation faced by me.
I'm waiting for 2 Accessory DP4100
Probes X100.
With afloat DSO, the Cric Clips of the 2 DP4100 X100 grounded to earth and the probes on the two phases?
Wouldn't it be safe for me , the OScope and the electrical system?
Awaiting your kind response!
You *must* have a single ground. I mean a grounded spike to which all grounding convey, including the PE line. Power the oscilloscope referencing to that ground. Then use a couple of active differential probes rated at not less than 1000V. The measurement must be performed knowing the procedures of how to handle high voltages and you must know what you're gonna do because this could be lethal! I won't take liabilities. On the oscilloscope use math functions to know the difference between the two AC sources. You mention 460V RMS and ~651V RMS ...I don't think this is correct starting from 230VAC RMS, I'm afraid you keep confusing RMS with peak and peak to peak. Oscilloscopes *always* display peak to peak voltages. For voltages out of phase you can't really use the root square of 2 to go back and forth RMS.
About the problem you face with that inverter I have a similar issue with a hybrid solar inverter, made by Voltronic, China. I have had no chance to investigate the problem deeply enough but it seems the problem arises from the fact that the inverter must disconnect neutral from ground when running over the grid, and reconnect it to ground when running over solar panels and batteries (UPS mode). What you describe, two separate neutrals, seems quite weird but for those inverter designed to run on two phases grids (no neutral) that are in use in some corners of the world.
It seems an interesting case.
Mains operated O-Scopes are grounded by the mandatory earth wire to guard off againts the radio waves, electromagnetic interference from nearby equipment or internal echos from O-Scope itself! Ain't I right?
Когда будет продолжение с постройкой токарного станка?
Sorry dude, don't understand. The automatic translation doesn't make any sense.
What about battery operated oscilloscope?
Didn't I mention it in the video? A battery operated oscilloscope is obviously not susceptible to cause troubles since there is no PE. But these kind of oscilloscopes are designed to work this way, so they have insulated probes and the oscilloscope's case is fully isolated with some kind of insulant.
Joke's on you, my place's wiring is old and all the retrofitted grounded power sockets just leave the ground floating (-_-)
Okaaay, yeah, not a shock hazard or anything, but since you're just joking...
Wow !
Very good explanation and nice drawings.
Like thus your presentation style ("if you like a dangerous live", "this is not ElectroBOOM",...) and that you definitely know what you are talking about.
It would be interesting to know something about your professional and educational background, because what you are presenting is certainly not from the hobby "maker" scene, but indicates profound knowledge and a lot of experience.
Where are you from? Where u get your education - i guess somewhere from an ex "communist" country?
Also, i like that you don't show only an oversized expensive "buy and use" (at "your" affiliate link - to sponsor your youtube hobby...) ready product , instead you show a good cheap and long proofed, safety(enough - if "you" have to die it will happen also crashing airplane could hit you...) solution.
Thumbs up, quite a lot of "cool professional electrical engineering" (oh well...)channel self-promoter could learn a lot of from your knowing and even more how you present your self to be modest and how to take the audience seriously (not this "hello brother" " hello folks" stupid semi friendly for just want to sell something and looking for clicks...)
Thanks. Under my political perspective the country I come from still is "communist" LOL ...but actually on the western side. You might be fooled by my accent because in spite living in a country where most speak a romance language, my mothetoungue language was affected by ancient German roots. I won't go into further details, sorry.
As the ancient alchemists used to be, I have an educational foreground, not background.
Greetings from the Alps.
9:42
I suppose at this point you meant 230uA rather than 320uA? O.K.?
What are the safely full scale voltage measured by O-Scope with X1 and X10? Are these 3.2 and 32 VDC or RMS?
990 KOhm is almost 1000 KOhm or 100 MOhm to constitute a Probe 100X while in unison with standard 10X one.
In my humble opinion, wouldn't have it been better if the Standard Probe used in X1 confuguaration for safety of the O-Scope?
And all calculation done on the later basis?
Help me if I'm confused.
I'm a medical doctor happened to be an accidental scientist: may be on wrong side!
I've never used any O-scope other than patient bedside monitors. My first ever entry level Chinese Rechargable, Dual Ch, SigGen O-Scope+DMM (ZEEVEII-3D12) with Voice-Assistant reached me 2-3 days ago. In search of safe use of the same I touched your UA-cam channel.
In my life, I've been moved by a few, and you are one among those, I happily ❤️ declare.
Help me please if I'm confused or wrong!
Thank you.
First off thanks for commenting. Indeed your comment could be of help for others. It could be helpful because many could confuse some points that clearly I have taken for granted when they'd not ...that's the curse of people with experience :)
The current value is correct: around 320uA @ 230VAC. So why it is correct?
An oscilloscope do not take the RMS voltage but the peak(+DC) voltage, while it shows the peak to peak voltage.
I know, this may arise even more confusion, but don't worry, follow me.
Let's take a sine wave that you want to measure at the oscilloscope. The instrument will show the sine wave from a reference point that is the GND (ground) level. In respect to GND the alternate sinusoidal signal swings from zero to full positive; then back to zero (GND); then down to full negative and finally back to zero again, where the cycle start over again.
So what you actually see on screen is a wave that swings from peak to peak.
However what matters for the input circuit is the voltage peak as an absolute value, which is the maximum allowed voltage in respect to ground irrespective of the polarity. Indeed if we look at the specifications of an oscilloscope they tell us the maximum input voltage that is meant as peak+DC voltage. In other words it is the absolute maximum voltage, be it AC or DC.
So speaking about a possible voltage to measure I took as a reference example 230VAC, the mains voltage in EU. Mains voltage is alwasy declared as RMS voltage. So, for a sine wave with a 230 RMS voltage, for the purpose of finding the voltage that the oscilloscope's input matter we need to find out the peak voltage.
Which for such a sine wave is: 230 times the square root of two, or simply 230 * 1.41 = 324.3 Vpk.
When we compute the current across a resistor usually we compute it as DC or peak value, rarely as RMS value. And since we want to know the voltage at the input of the oscilloscope we have to calculate the peak value.
So the math is as follow: Input voltage 324 Vpk / (990Kohm + 10Kohm) = 324uA. Remember, the current flows through both resistors to GND. Now because we know the current, and because the same current flows on both resistors, we can compute the voltage across the 10K resistor: 324uA * 10K = 3.24Vpk.
Notice we should also consider the input impedance of the oscilloscope which happens to be in parallel with the 10K resistor. Though since this impedance is about 1Mohm at DC (or at very low frequencies such as 50 or 60 Hz) it doesn't change much our computations: 1/ ((1/1M) + (1/10K)) = 9900 ohm, actually an added attenuation of 1% .
The probe x1 change anything as it is just a chunk of wire.
Now, about the safe usage of the instrument, understanding that you are not that experienced, I'd recommend you to avoid taking measurements from mains. Instead use it to make measurements of small voltages of devices fully insulated from mains. In such a case it is quite safe to use in any condition. I never heard of that brand/model of oscilloscope, BTW.
Hope this will be helpful.
P.s. Thanks for love. Love+Peace.
@@AccidentalScience
I got your point!
For all practical purposes, regarding AC voltage or current we talk about it's effective value, the root mean square RMS value that is equivalent to its counterpart DC's heating effect.
It's the peak value of the AC V or C 'times' the Inverse of Square Root of 2 = 0.7071
In true measurement one has to consider the Peak Voltage or Current of the AC that's RMS value times √2=1.4142.
So it would be around 325 uA.
This has to be accommodated resistance and capacitance calculation. I'm grateful for reminding me!
so basically make a differential probe instead of buying one hehe
For simplicity we will use a single phase oscilloscope! 🤣 Great video btw!
Did I say that? OMG! 🤣 Where?
👌👍💐
❤ i love you MEN 🫡
I probably wouldn't want to go as far as the previous speaker, but I find your videos very informative and very well explained so far. I'm really pleased to have stumbled across your channel and it looks like I'll be popping in more often.
@@Waldemar_la_Tendresse don't worry, I love you too!