wn4isx

#99423

What exactly are you trying to see?

There has been a lot of interesting discussions on how to "safely" connect an oscilloscope to the AC Mains.

?

So, what is your goal?

What are you trying to see on the AC?

What is your AC Mains voltage?

Is there a safety/protective ground?

What is your skill set? College electronics class? High school electronics class? Self taught by trail and error??

What is your age? That fits in with what is your skill set.

This isn't intended to be insulting, I was playing by shock and learn before formal education, a vocational school program that today grants Associate Degrees, then I worked for 2+ years before I was tricked into starting college for a BS in electrical engineering. Many (?most?) of the people in this group have similar informal education, followed by some form of formal training.

?

We can offer advice for problems and goals we've all had but they are probably worthless to your goals.

?

I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.' If all you want to do is to see an AC Mains waveform. I'll capture the 120V 60Hz AC Mains in our home with a PC sound card and my 9k:1k attenutator and post 60 seconds of 48K high resolution wav audio in the files section.

?

My 9k:1K attenuator came from a project at work, I kept it and rebuilt it in a Budd minibox with a standard?

IEC C14 male connector with a female 1/4" stereo audio connector.?

Note: This is never used for RF, only for AF and has been used about 5 times in the last 30 years.

I keep it because it might be useful...someday.

?

This is a link to the his oscilloscope

?

I traded for a Zoyi ZT-701s, very similar to your unit.

Zoyi multimeter+oscilloscopes - ZT-70xS,

It is a two channel 'scope ' and works fine with my 9k:1k attenuator on the AC.

?

But you can still fry your self if you aren't careful.

?

Or

?

The waveform will be so close to the AC mains you probably can't tell the difference.

?

The only real difference will be AC Mains will have various distortion components that a pure waveform won't have, but you'll have extreme difficulty seeing the distortion on a scope, you'll need to feed the AC Mains to a PC sound card. Sample at 96K minimum, higher if possible, and do a high resolution FFT.

?

And connecting the AC to a PC is a good way to fry a PC, PC inputs can not handle more then perhaps 3V peak to peak. And this is a whole new set of problems and nightmares.?

?

#99424

开云体育

Hi,

>> So, what is your goal?

Mostly to learn how to do it safely. ? What I’ve learned in my past, it’s good to know stuff before I need to know it. ? I tell kids I mentor that we (maybe) need 1/10 of everything we might learn in school. ?But the problem is that we don’t know which 1/10 is important so we learn all that stuff ahead of time.

So I’m asking to learn now, just in case I might need to know sometime in the future. ?Maybe I’ll get solar panels and maybe I need to scope out the inverter output one day.

?= ?= ?= ?= ?= ?= ?= ?=?

>> What are you trying to see on the AC?

I bought a UPS backup power supply. ? It’s supposed to be “modified sine wave”. ? When I scoped it out, it’s nothing like the classic square stepped wave form. ? This is what I wanted to see (the advertised vs real waveform)

?= ?= ?= ?= ?= ?=?

>> What is your AC Mains voltage?

While the UPS backup power supply voltage is supposed to be 120v, I’m not sure if it can be considered “mains voltage”. ?Is it ? ? I don’t know. ? Anyway, I usually try to stay away from anything over 12v but hey, it doesn’t hurt to ask here

?= ?= ?= ?= ?= ?= ?=?

>> Is there a safety/protective ground?

The UPS device doesn’t have ground.

?= ?= ?= ?= ?= ?=?

>> What is your skill set? College electronics class? High school electronics class? Self taught by trail and error??

Self taught. ?Some trial. ?Some error.

I’m alive because I try to stay at low voltage (12v and below).

?= ?= ?= ?= ?= ?=?

>> What is your age? That fits in with what is your skill set.

I’m aged 61. ? I’ve been interested in electronics since I was 6 YO. ? Around age 35, I had my first “ah-ha” moment in electronics when I got my first oscilloscope.

?= ?= ?= ?= ?= ?=?

I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.'

But it isn’t always PURE sine wave. ? In fact it’s not even the advertised stepped ?/ modified sine wave. ? This is what I wanted to know (how far is their “modified sine wave” from the diagram they had on the box.

?= ?= ?= ?= ?= ?= ?=?

>> This isn't intended to be insulting, I was playing by shock and learn before formal education, a vocational school program that today grants Associate Degrees, then I worked for 2+ years before I was tricked into starting college for a BS in electrical engineering. Many (?most?) of the people in this group have similar informal education, followed by some form of formal training.

I’m not sure what my age have to do with my question about scoping 120v mains. ? My friend’s son just graduated with EE from my state university (this past summer). ? He knows much more about EE in a wide aspect, but when it comes to things like circuit design, it turns out I’m actually better at that then him because that’s what I like about electronics. ? For me “electronics” and circuit design are the same thing (in fact that’s all I’m interested in when it comes to electronics). ? For him it’s everything from high voltage power transmission, VSLI chip design, as well as circuit design.

?= ?= ?= ?= ?= ?=?

So back to my question : I have a portable (battery operated) DMM style oscilloscope. ? I actually have many scopes (few usb types, one 120v powered, one portable). ? If I needed to scope a 120v device, is it safe or even recommended to use portable (battery powered) dmm style oscilloscopes ? ? Or is it still ONLY recommended to use differential probe adopter ?

Jong?

On Dec 12, 2024, at 1:32 PM, wn4isx via groups.io <wn4isx@...> wrote:

?
What exactly are you trying to see?

There has been a lot of interesting discussions on how to "safely" connect an oscilloscope to the AC Mains.

?

So, what is your goal?

What are you trying to see on the AC?

What is your AC Mains voltage?

Is there a safety/protective ground?

What is your skill set? College electronics class? High school electronics class? Self taught by trail and error??

What is your age? That fits in with what is your skill set.

This isn't intended to be insulting, I was playing by shock and learn before formal education, a vocational school program that today grants Associate Degrees, then I worked for 2+ years before I was tricked into starting college for a BS in electrical engineering. Many (?most?) of the people in this group have similar informal education, followed by some form of formal training.

?

We can offer advice for problems and goals we've all had but they are probably worthless to your goals.

?

I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.' If all you want to do is to see an AC Mains waveform. I'll capture the 120V 60Hz AC Mains in our home with a PC sound card and my 9k:1k attenutator and post 60 seconds of 48K high resolution wav audio in the files section.

?

My 9k:1K attenuator came from a project at work, I kept it and rebuilt it in a Budd minibox with a standard?

IEC C14 male connector with a female 1/4" stereo audio connector.?

Note: This is never used for RF, only for AF and has been used about 5 times in the last 30 years.

I keep it because it might be useful...someday.

?

This is a link to the his oscilloscope

?

I traded for a Zoyi ZT-701s, very similar to your unit.

Zoyi multimeter+oscilloscopes - ZT-70xS,

It is a two channel 'scope ' and works fine with my 9k:1k attenuator on the AC.

?

But you can still fry your self if you aren't careful.

?

Or

?

The waveform will be so close to the AC mains you probably can't tell the difference.

?

The only real difference will be AC Mains will have various distortion components that a pure waveform won't have, but you'll have extreme difficulty seeing the distortion on a scope, you'll need to feed the AC Mains to a PC sound card. Sample at 96K minimum, higher if possible, and do a high resolution FFT.

?

And connecting the AC to a PC is a good way to fry a PC, PC inputs can not handle more then perhaps 3V peak to peak. And this is a whole new set of problems and nightmares.?

?

wn4isx

#99425

OK an oscilloscope is probably the wrong tool for this job. Consider a battery powered laptop operating on battery power with a resistive attenuator.

Laptop internal audio line inputs run anywhere from 5K to 50K.

?

I'd go with a 10:1 attenutaor, high resistance to high, junction of high [tip or ring] resistance to low resistance to sound card hot in, low side of low resistance to neutral and sound card low [sleeve].

I'd place 6 1N400x diodes, 3 in series wired antiparallel. Anode of one string to cathode of the other string to limit the maximum voltage to ~2.1V.

?

I like Dale aluminum shell resistors that can be mounted to metal. Ground the metal for safety.

I use 9k from hot to 1K with goes to neutral. I'd place a 10k pot across the 1k and adjust for 1V with a DVM.

?

Record with a program like Audacity, a freeware program. I'm not familiar with freeware FFT software but Audadcity does have FFT, I have no idea how good it is.

?

"Yes, Audacity does have an FFT (Fast Fourier Transform) display, which is accessible through the "Spectrogram View" feature, allowing you to visually see the frequency components of an audio file over time by utilizing the FFT algorithm to analyze the data;?you can also access a "Plot Spectrum" function to view a single snapshot of the frequency spectrum of a selection within your audio file, also based on FFT calculations.?

Key points about Audacity's FFT display:

·??????????????????????????? Access:

To view the FFT display, go to the track menu and select "Spectrogram".?

·??????????????????????????? Function:

The spectrogram shows how the energy distribution across different frequencies changes over time.?

·??????????????????????????? Plot Spectrum:

To see a single snapshot of the frequency spectrum, go to "Analyze > Plot Spectrum".?

·??????????????????????????? Underlying Calculation:

Both the spectrogram and plot spectrum use the Fast Fourier Transform (FFT) algorithm to analyze the audio data

FFT will display the spectra with harmonics, the time display will show a normal waveform, which, unless there is more then ~10% harmonic distortion, probably won't be visible.

?

Now for UPS 'quasi sine wave' outputs, the time display may well show you some really odd waveforms.

?

I don't use Audacity, I use Adobe Audition, which has similar capacities but is not freeware. Way not freeware. Obscenely expensive.

?

Please remember the dangers remain the same.

?

Record the waveform, then disconnect the AC and play with Audacity.

?

My rule of thumb is to stay connected to dangerous voltages only as long as necessary.

?

We compared an expensive Rigol DSO FFT with a mediocre laptop for audio FFT, the cheap PC blew the Rigol away.

?

Part of any measurement process is picking the best tool(s). That can be difficult with all the sales hype for scopes etc.

?

I asked about age because at 14 I knew everything and took way too many chances. At 61 you've lived long enough to know your limits. So the age of someone I don't know becomes an issue when trying to offer technical help.

?

I added a phone to a girl friend's (not romantic) bedroom. Hid the wiring, removed the bell, life was good, until the phone rang when I had one wire connection in my mouth while completing the other.

?

Let's just say the sudden wetness at my crotch was the least of my concerns. 90V at 28Hz flowing through your mouth to your hands is an extremely interesting experience. I was 14 and my thinking was normal for a 14 year old, I didn't think far enough ahead.

?

And yes I realize how dangerous that was and how lucky I was to only have wet pants.

?

So age is a valid question when dealing with hazardous voltages.

#99427

On Thu, Dec 12, 2024 at 06:32 PM, wn4isx wrote:

I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.'

I agree, a sinewave is not interesting - but sometimes the mains waveform is not a sinewave, and then you really really need a 'scope to see it..

?

Back in college, I remember that the lab's AC mains was a very distorted wave.? We had rumors about why, but I do not recall being told the truth from a reliable source.? It was understood that there was some sort of device in the building's basement (transformer? motor-generator?) that was responsible for the lousy waveform.

?

Around the same time, give or take a few years, I became somewhat interested in the AC mains waveforms mostly because of power transformers that would go up in smoke - and a few other reasons.

?

It was said that anyone could tell whenever the local synchrotron was online because there would be a significant glitch at a certain point in the 60 Hz mains waveform.? I don't know if it was true but it was one of the things we had to consider.

?

Also there was the time the local power company changed some HV power wiring which resulted in extremely noisy signal monitoring over rented telephone company wires (this was decades ago).? Talks with the utility company's engineers suggested that their changes resulted in a significantly bigger common-mode current through earth, of the harmonics of 60 Hz - suggesting that the 60 Hz waveform was not very clean to begin with in that section of the mains distribution network.

?

These days, there are those ugly "modified" or "pseudo" sine waves that are digitally generated.

?

I'd argue that using an isolation transformer could significantly change the waveform's shape and can mask the problem you are looking for.

?

A 9K:1K attenuator is great - IF you can be certain which lead is always the neutral.? I hear many stories about building wiring that is not right, so I think I would not want to use that arrangement which can make the scope's chassis 'hot'.

?

Use a 'scope when it's needed, and if you do, use it wisely!

?

Just my opinion.

?

Andy

?

wn4isx

#99429

I'll be the first to agree the AC Mains is seldom [?never?] a pure sine wave.

?

I suspect the mains have higher distortion today then when we were in college because of all the switch mode power supplies and variable speed drives.

?

But an oscilloscope is hardly the ideal tool for looking at AC Mains distortion. It is difficult to see less then ~3% harmonic distortion. Some people with the magic eye can see 1%. I'm not one but my boss when I worked in a small electronics shop was, but even he preferred to use the right test gear.

?

This is where FFT (Fast Fourier Transform") display shines. It will show you the fundamental and all the harmonics and noise at higher frequencies.

?

Even a storage oscilloscope won't give you the same information FFT will. It is create however for seeing the spikes caused by silicon diode turnoff (commutation noise).

?

Now the right test gear in 1974 for most of us was HP, they used to offer a tunable AF voltage meter that allowed you to note the level of a reference frequency, then tune to each harmonic and record them, that way you could show the THD of an amplifier and it was a real PITA to use.

?

FFT gives you the same information immediately.

?

Some high end DSO [Digital Storage Oscilloscopes] provide FFT but all the ones I've seen fall short of what a mediocre PC sound card and a freeware FFT program can reveal.

?

I did a quick net search because I use commercial programs and custom software for my audio analysis but this program looks good "Visual_Aanalyzer_Freeware"

https://roga-instruments.com/fft-spectrum-analyzer-freeware/

?

I generated a 1000 second (why rush) 1kHz sinewave with Adobe Audition and used a physical loopback, line out to line in patch cable, to produce the worse possible playback/record on my HP. When I overdrove the output, lots of harmonic spikes showed up in the FFT display. I created a 100Hz square wave and it produced the expected array of harmonic spikes.

Note: The HP laptop sound "card" is almost OK with music, nothing to write home about but fails completely with even a 100Hz square wave, the wave is integrated and looks odd on a time (oscilloscope type) display.

?

Rod Elliot has a nifty "distortion generator" that will give you symmetrical or asymmetrical distortion.

https://sound-au.com/articles/distortion-f211.gif

?

You can achieve the 600 ohm input with a common emitter or JFET common source follower.

Mine is in the shop, it's early and 23F here and my shop isn't heated. Too damn cold!

?

I suspect any of the inexpensive Behringer USB audio "cards" will beat all but the most expensive DSOs.

?

I use 1N400x diodes to protect audio inputs because the normal choice, 1N914 or IN4148 fail open when grossly overloaded while the 1N400x have always failed shorted in my experience.

?

The modern 1N4004 turns off fast enough to not be an issue up to at least 20kHz. I wouldn't use one in a switch mode power supply but there is very little energy above ~10kHz in normal audio including any type music you want to name. The harmonics fall off pretty quick.

?

[The modern 1N4004 has a specified reverse recovery time of 2uS, which gives and upper usable frequency of ~500KHz.]

?

Use a program like Audacity to do a sharp high pass software filter at 10kHz and look at what's left from a good source like a CD.

?

The physics lab had a small particle accelerator that made incandescent bulbs hum when they ran it. It made fluorescents trip their breakers. ?I have no idea what type power supply it used but it must have been the dirtiest design possible. At the time I wondered 'does it meet FCC Part 15 emission regs?'

?

They never ran it during the day when classes were in session. Now during practical labs at night.... and I always carried a Geiger Counter for practical labs.

?

"A 9K:1K attenuator is great -?IF?you can be?certain?which lead is always the neutral.? I hear many stories about building wiring that is not right, so I think I would not want to use that arrangement which can make the scope's chassis 'hot'."

?

First, I would never use my 9k:1k with a mains powered, or mains connected anything. Never ever!

?

And my 9k:1k attenuator is a deadly venomous snake just waiting to bite you if you are careless, it makes the most venomous reptiles in nature mild by comparison. But it's also the only way I know of to "safely" not introduce unwanted distortion that I know of.

?

That's why I'm so silly with warnings. I do not want to be responsible for anyone frying themselves. Getting my self shocked was bad enough. Getting someone injured or killed would be horrible. Which is why is stress "Do you really need to do this?"

?

BTW, I replaced every outlet in our home with "spec grade" and found 2 that were wired backwards. I'd never use this beast in a new location without verifying the hot is hot and neutral is neutral. I even worry about the ground being hot. BTDT and fried some equipment in the new wing of a hospital. ?

?

I've been known to test extension cords for proper wiring, then connect them in series to extend an "outlet" to a cold water pipe to actually measure hot is hot and ground ain't.

[I'm paranoid but am I paranoid enough?]?

------------------------------

Sidebar, an oscilloscope is useless for seeing RF EMI on the AC Mains unless it is way above FCC limits. 100uV [no load] of a 1MHz square wave from a canned TTL oscillator, with attenuator and capacitor isolation, will produce S9+40 all through a home. Real world experiment not theory.

?

https://www.w0qe.com/RF_Interference/simple_rfi_generator.html

?

I have several, all have additional attenuation in the output to the AC Mains.

?

wn4isx

#99430

A friend suggested this program as it has normal oscilloscope display, phase (XY) Lissajous, FFT, and a signal generator.

"Visual_Aanalyzer_Freeware"

at

https://www.zeitnitz.eu/scope_en

?

The FFT display is labeled "Frequency" for some unknown reason. It has a zoom function that is rather useful.

?

At the moment our 240V AC Mains has 3.8% to 4.5% harmonic distortion. It varies randomly. I wonder what effect a few hundred thousand people turning on their coffee makers has.....

?

I have a 240V outlet at my radio desk just in case I ever want to get serious about ham radio and add a 5kw RF amp. [yea right after hell freezes over] It's really for a special space heater an electrician friend located for me.

[That warmed my room from 68F to 75F in 30 minutes. I've found I don't tolerate cold as well at 73 as at 16. Bummer.]

?

The phase, which indicates short term, "instantaneous," frequency variation, goes wild at ~6:30 about the time the harmonic distortion also goes nuts.

?

I have a 10MHz GPS disciplined oscillator with a magic PIC 10MHz to 60Hz (zero jiter) that I feed into the vertical and attenuated 60Hz from the AC mains into the horizontal. The Lissajous "circle" jitters like crazy until ~9:00AM when it "stabilizes" [sort of] then goes nuts around 4:00PM until ~7:00PM.

?

Yea I know I have some really odd hobbies that will probably kill me someday,

?

And yes it's a bit hypocritical that I routine monitor the AC Mains, but I'm extremely careful, have designed interfaces that are as safe as I can make them and the outputs are "idiot proof."

#99436

On Thursday 12 December 2024 09:09:57 pm wn4isx via groups.io wrote:
Record with a program like Audacity, a freeware program. I'm not familiar with freeware FFT software but Audadcity does have FFT, I have no idea how good it is.
Hmm,  I didn''t know that was in there.  I just looked,  and that program happens to be installed on this machine.  I'll have to play with that a bit...

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

#99469

Just yesterday my 4 year old grandson and I were playing with my scope. He put his finger on the probe end and I adjusted the sweep and amplitude to get a presentable display. The 60 Hz pickup was horrible. Since I changed my shop lights to LED's, I would have thought the Mains would have been clean. I am not going to investigate the source of the noise but it is interesting that the radiated signal is so bad.

Dan Kahn

On Friday, December 13, 2024 at 12:46:41 AM EST, Andy via groups.io <ai.egrps@...> wrote:

On Thu, Dec 12, 2024 at 06:32 PM, wn4isx wrote:

I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.'

I agree, a sinewave is not interesting - but sometimes the mains waveform is not a sinewave, and then you really really need a 'scope to see it..

?

Back in college, I remember that the lab's AC mains was a very distorted wave.? We had rumors about why, but I do not recall being told the truth from a reliable source.? It was understood that there was some sort of device in the building's basement (transformer? motor-generator?) that was responsible for the lousy waveform.

?

Around the same time, give or take a few years, I became somewhat interested in the AC mains waveforms mostly because of power transformers that would go up in smoke - and a few other reasons.

?

It was said that anyone could tell whenever the local synchrotron was online because there would be a significant glitch at a certain point in the 60 Hz mains waveform.? I don't know if it was true but it was one of the things we had to consider.

?

Also there was the time the local power company changed some HV power wiring which resulted in extremely noisy signal monitoring over rented telephone company wires (this was decades ago).? Talks with the utility company's engineers suggested that their changes resulted in a significantly bigger common-mode current through earth, of the harmonics of 60 Hz - suggesting that the 60 Hz waveform was not very clean to begin with in that section of the mains distribution network.

?

These days, there are those ugly "modified" or "pseudo" sine waves that are digitally generated.

?

I'd argue that using an isolation transformer could significantly change the waveform's shape and can mask the problem you are looking for.

?

A 9K:1K attenuator is great - IF you can be certain which lead is always the neutral.? I hear many stories about building wiring that is not right, so I think I would not want to use that arrangement which can make the scope's chassis 'hot'.

?

Use a 'scope when it's needed, and if you do, use it wisely!

?

Just my opinion.

?

Andy

?

#99474

开云体育

I think that your AC line signal is a lot cleaner than what you saw.

The radiated signals are usually a lot worse.

Bertho

?

Show quoted text

From: [email protected] <[email protected]> On Behalf Of Dan Kahn via groups.io
Sent: 16 December, 2024 9:54
To: [email protected]
Subject: Re: [electronics101] To jong kung

?

Just yesterday my 4 year old grandson and I were playing with my scope. He put his finger on the probe end and I adjusted the sweep and amplitude to get a presentable display. The 60 Hz pickup was horrible. Since I changed my shop lights to LED's, I would have thought the Mains would have been clean. I am not going to investigate the source of the noise but it is interesting that the radiated signal is so bad.

#99478

On Monday 16 December 2024 09:54:08 am Dan Kahn via groups.io wrote:
?Just yesterday my 4 year old grandson and I were playing with my scope. He put his finger on the probe end and I adjusted the sweep and amplitude to get a presentable display. The 60 Hz pickup was horrible. I remember doing that ages ago,  probably around the time I got one of my first scopes.  What are you seeing?  I know that what I saw wasn't even close to a sine wave...

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin