Measuring mains AC noise with o'scope - Page 1
Forum section: electronics / beginners

author: oh_no
author_rank: Contributor
timestamp: September 22, 2020, 07:01:31 pm
content: In the video below, what's that device --to the left of the o'scope --that probe leads (from scope) are connected to?Brand and model number would be cool! Thx.

author: Benta
author_rank: Super Contributor
timestamp: September 22, 2020, 07:59:25 pm
content: Differential probe to save you from killing yourself. Looks home made..

author: oh_no
author_rank: Contributor
timestamp: September 22, 2020, 08:32:47 pm
content: Quote from: Benta on September 22, 2020, 07:59:25 pmI see a name on the case (brand / model??). Maybe it was re-purposed from another device's case.Anyway, to measure noise at the sensitivity of that shown in the video (milli-volts, maybe micro-volts), should the diff. probe design be anything special?

author: oh_no
author_rank: Contributor
timestamp: September 22, 2020, 08:52:58 pm
content: Quote from: oh_no on September 22, 2020, 08:32:47 pmWell, I assume the tips Shahrirar gives here are a good place to start ....https://youtu.be/d_Ybe6xnMIg... now, let's find one that doesn't break the bank, but still provides good, reliable, andrepeatableperformance.

author: james_s
author_rank: Super Contributor
timestamp: September 22, 2020, 09:53:58 pm
content: Why does every beginner always want to measure mains with their scope? That's not really what scopes are intended to do, and you are not likely to learn much. If you do have a need to scope such things buy a differential probe, there are deals to be had, I have two different ones that I got for around $100 each.

author: oh_no
author_rank: Contributor
timestamp: September 22, 2020, 11:39:20 pm
content: Quote from: james_s on September 22, 2020, 09:53:58 pmDid you REALLY even read thru this thread before you posted this?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 22, 2020, 11:59:54 pm
content: Quote from: oh_no on September 22, 2020, 11:39:20 pmI did and I don't see a reason for you to become defensive about it. I tend to agree that it is a common theme with beginners. One thing you may want to consider posting your question under the video you linked. They may explain where it came from.I didn't follow what the person in the video was describing with the common mode and digital ICs or what ever they were going on about. I had made my own LISN.At one point I was wanting to look at the mains as well and just tossed a transformer and LEM sensor into a box. The transformer is an odd looking metal can (posted about it here) that had enough BW to get me into the 40th harmonic. A little over sampling and some software to model the DSO and take care of some of the non-linearities. This video goes over the math and shows it in operation.

author: james_s
author_rank: Super Contributor
timestamp: September 23, 2020, 05:09:48 am
content: Quote from: oh_no on September 22, 2020, 11:39:20 pmYes, and I just read it all again and I still don't see anything that would make me change what I said. What are you getting upset about? Have you not seen the dozens of other posts by noobs wanting to look at the mains with a scope?

author: tggzzz
author_rank: Super Contributor
timestamp: September 23, 2020, 07:26:27 am
content: Quote from: oh_no on September 22, 2020, 11:39:20 pmGiven what you wrote, the response is not unreasonable. Of course none of us can guess what you didn't write!You really should read and understand the safety and praxis references inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: oh_no
author_rank: Contributor
timestamp: September 23, 2020, 07:42:37 am
content: Quote from: james_s on September 23, 2020, 05:09:48 amI am ENTERTAINED that it is you who is upset by my response.QuoteNo. And there is absolutely NOTHING wrong with wanting to look at mains with the scope .... with the proper precautions. Hence the orig. query. Again ... it might help if you read the orig query a bit more CAREFULLY before posting pointless remarks.

author: oh_no
author_rank: Contributor
timestamp: September 23, 2020, 07:45:04 am
content: Quote from: tggzzz on September 23, 2020, 07:26:27 amYour response makes absolutely no sense.

author: tautech
author_rank: Super Contributor
timestamp: September 23, 2020, 07:50:26 am
content: Quote from: oh_no on September 23, 2020, 07:42:37 amAnd what might those be ?You need understand this is a worldwide forum with readers from all levels of experience and competence therefore generic advice is to NOT connect a scope to mains.

author: oh_no
author_rank: Contributor
timestamp: September 23, 2020, 07:53:17 am
content: Quote from: joeqsmith on September 22, 2020, 11:59:54 pm??Not sure why you linkedthisvideo?? The one in which you made your own DIY perfboard diff. probe is more topical.

author: oh_no
author_rank: Contributor
timestamp: September 23, 2020, 08:01:09 am
content: Quote from: tautech on September 23, 2020, 07:50:26 amY'all are seeing issues that were never part of my orig queries. Go back to the top and re-read my posts. I did not ask for opinions on safety. And it is a bit presumptuous of anyone to assume "levels of experience" based on post count or newness to this forum.If you want to help, see the top post.

author: tggzzz
author_rank: Super Contributor
timestamp: September 23, 2020, 08:47:15 am
content: Quote from: oh_no on September 23, 2020, 08:01:09 amWe use our very considerable experience to infer experience and knowledge (and lack of it) from the quality of the writing, the quality of the question, and other aspects.QuoteIf you actually want help, change your attitude.

author: Ian.M
author_rank: Super Contributor
timestamp: September 23, 2020, 09:46:56 am
content: The Tripp-lite video linked by the O.P is pure unadulterated bullsh!t and marketing w@nk! Apart from a stack of multi-socket adapters that would make a fire-marshal wince, the 0.5V 'limit' for ground noise comes from near-obsolete bipolar TTL logic thresholds and has nothing whatsoever to do with noise voltages measured between Neutral and Ground at the wall outlet, which may (or may not) accurately represent common mode noise.Basically TTL logic chips were built of bipolar transistors, and couldn't pull a logic '0' output right down to 0V due to the low side output transistor's Vce_sat. This was about 0.3V, maybe a bit lower in ideal circumstances. The specified logic '0' input threshold was 0.8V, below which any signal was guaranteed to be seen as a '0'. The actual threshold at which the gate switched would be a bit higher, between the specified logic '0' and logic '1' thresholds, but you couldn't count on the extra margin. Subtract 0.3V from 0.8V and you get 0.5V, which is the maximum amplitude 'ground bounce' that could be tolerated at the Gnd (0V) pin of a TTL chip with respect to the Gnd pin of any other chip it was connected to. This is all low voltage 5V DC stuff, nothing whatsoever to do with the power coming from the wall. There certainly wouldn't be a connection from Neutral to the logic board. Also, PSUs don't (and never did) contain TTL logic connected between Neutral and Ground on the input side!The demo in itself is rather suspicious. Its obvious something is filtering out the 60Hz power-line fundamental frequency from the Tripp-lite 'engineer's scope display. There shouldn't be very much of it on the Neutral to Ground trace, but I would expect some signs of it. On the raw Line to Ground signal, there is a whopping great 117V RMS, 331V pk-pk 60Hz sine wave, probably with distorted peaks ('flat-topping') due to other loads in the building and neighborhood consisting of SMPSUs without good power factor correction, with the line noise riding on top of it. Obviously that's undesirable when you are trying to measure low amplitude noise on top of it as most scopes wont have the resolution to resolve small signals riding on one several orders of magnitude larger. Filtering or cancelling out the fundamental frequency to a sufficient degree to be able to directly measure noise at the tens of mV level would be extremely challenging. You've got to attenuate it by over five orders of magnitude without significantly attenuating the noise you are trying to measure. This would be possible if the mains supply was a fixed frequency pure sine wave, but it drifts slightly with the load on the grid, with up to +/-0.05Hz variation being entirely normal and excursions up to about +/-0.1Hz not unusual. This makes it impractical to use a high Q notch filter to reduce the fundamental by sufficient orders of magnitude (as you'd have to keep tweaking its tuning to follow the line frequency to get adequate rejection), so either the 'magic box' measurement interface is filtering out *ALL* low frequency signals including low frequency noise, or its doing some very complicated DSP to track the fundamental frequency and its odd harmonics (from the 'flat-topping') and actively cancel them. In practice, its commonest to simply high pass filter the power line signal and effectively ignore all noise below the filter cut-off frequency.If I was a suspicious sort, I'd not want to bet that the 'magic box' wasn't entirely rigged, maybe with a high bit rate audio player loaded with tracks of various sorts of noise, controlled remotely by someone off-camera.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 23, 2020, 06:42:27 pm
content: Quote from: oh_no on September 23, 2020, 07:53:17 amSeems like the standard for THD was 40 harmonics up. Video just shows the math to correct for the scopes errors. That one differential probe (I showed three) certainly has a higher bandwidth but it may not be good enough for what you want. These are fairly inexpensive to buy.I noticed you had not requested any information from the company who created the video you links so I have asked for you.Quote from: Ian.M on September 23, 2020, 09:46:56 amAny time I have used digital logic, there may be two or more layers of power supplies. All with a fairly good PSRR. I was trying to think of why they felt it made a good example. I didn't get anything out of the video, at least nothing that would suggest I should buy their products.I doubt they rigged anything but I did feel I was being trolled by their marketing.

author: james_s
author_rank: Super Contributor
timestamp: September 23, 2020, 07:52:19 pm
content: Quote from: oh_no on September 23, 2020, 08:01:09 amWhy is it unreasonable to assume that? Your top post contains very little information. None of us know you, none of us know how much you know, none of us have any idea how experienced you are so we can only guess. In the absence of any of this naturally we are going to assume the lowest level of knowledge and given the safety issues involved in anything mains related it should be expected that people are going to warn you of them. Frankly your attitude is going to make things difficult for you here, we are not paid consultants here to serve you, we are not tech support, we are members of a global community consisting of people of all walks of life and experience levels. We volunteer our time to answer questions for each other and discuss engineering related topics, social interaction is a two way street. You don't make a lot of friends by walking into a room full of strangers and getting all bent out of shape when you don't immediately get exactly the support you are wanting. Joining a forum is much like walking into a pub you've never been to, you can't just expect everyone to know who you are and treat you as their friend as soon as you walk in the door.

author: oh_no
author_rank: Contributor
timestamp: September 23, 2020, 08:36:29 pm
content: How about this ... an improved AC filtering scheme?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 23, 2020, 08:53:29 pm
content: I must not be the target audience as I still don't see the point of the filter, or the point of making a video of the filter or the point of posting the video of the filter....

author: rstofer
author_rank: Super Contributor
timestamp: September 23, 2020, 09:20:44 pm
content: Quote from: oh_no on September 23, 2020, 08:36:29 pmVideo link removed...Maybe not!https://www.dailyexaminer.com.au/news/electricity-time-bombs-dirty-electricity-devices-p/2363843/

author: Benta
author_rank: Super Contributor
timestamp: September 23, 2020, 09:30:42 pm
content: Why are you all attacking this new poster?The original question was reasonable.People, this is the "beginners" section. Cool down.

author: bdunham7
author_rank: Super Contributor
timestamp: September 23, 2020, 10:47:01 pm
content: Quote from: oh_no on September 22, 2020, 07:01:31 pmI don't know the exact model they have there, but it is some form of high-pass filter that allows you to see the HF noise without passing any of the fundamental 50/60Hz mains power. It appears to have three ouputs, but I don't know how they are isolated or any details like that. It would be similar in function to this:https://www.bondline.com.au/images/uploads/images/Bondline_OnFilter_AN%20EMI%20Adapters.pdf

author: Brumby
author_rank: Unknown
timestamp: September 23, 2020, 11:16:58 pm
content: Quote from: Benta on September 23, 2020, 09:30:42 pmI don't see attacks. I see warnings ... warnings that the OP is taking exception to.QuoteIt may have been reasonable, but asking that specific question demonstrated a fundamental lack of knowledge in that area, which raises the question of safety.With an absolute lack of knowledge about the background of the OP, do we say something - or do we say nothing and pray they don't destroy equipment/incinerate a building/kill themselves ... or kill others? (Call me melodramatic if you must - but you know these are possibilities.)My vote is: to say something.QuoteYes, thisISthe "beginners" section - which iswhycertain safety considerations are being brought to the fore.As I see it, it's the OP that is getting hot under the collar because their expertise is being doubted. This can be easily remedied by the OP providing some background. Failing that, we are forced to consider whether this is a case of the Dunning–Kruger effect in play.Generally, we don't like to see members get blown up one way or another.

author: bdunham7
author_rank: Super Contributor
timestamp: September 23, 2020, 11:58:59 pm
content: Quote from: Brumby on September 23, 2020, 11:16:58 pmI have to take exception to that inference. Did you know exactly what that box was at first sight? Did anyone? I had to deduce its function by what was shown on the scope and then go look to find an example to be reasonably sure. And I'm still not 100% sure as the video is not good and I didn't find any product that looked very similar.

author: Brumby
author_rank: Unknown
timestamp: September 24, 2020, 12:53:03 am
content: You are right. I must apologise - but in doing so, I will point out that I was taking the thread title into consideration ... and the rest of the posts coloured my assessment.

author: Brumby
author_rank: Unknown
timestamp: September 24, 2020, 01:00:21 am
content: The presenter does actually refer to the box in question (multiple times) as a "line probe".I would usually refer to something like that as a power line monitor. Something that is possibly a little more complex than a differential probe, but having an equivalent signal output that's safe for scope use.

author: james_s
author_rank: Super Contributor
timestamp: September 24, 2020, 02:48:40 am
content: I didn't watch the video, watching videos takes far more time than I'm willing to invest to answer a random question. I went by the title of the thread and the text within it and assumed it was just another noob wanting to scope the mains.

author: oh_no
author_rank: Contributor
timestamp: September 24, 2020, 03:28:38 pm
content: I'm gonna assume that something like commercial-avail. micsig dp10013 is the way to go.... or, maybe even EEVBlog's own hvp70...https://goughlui.com/2018/12/16/review-eevblog-hvp-70-70mhz-micsig-dp10013-100mhz-high-voltage-differential-probes/https://www.eevblog.com/product/hvp70/

author: bdunham7
author_rank: Super Contributor
timestamp: September 24, 2020, 03:39:13 pm
content: Quote from: Brumby on September 24, 2020, 01:00:21 amWithout knowing the details, I wouldn't assume that it was differential or isolated at all. A simple robust ground-referenced RLC filter might be all there is to it. As far as I can tell, the function is to block the fundamental entirely and leave only the noise, which is accomplished by setting the filter turnover point at 10kHz or so. OTOH, it might be something else entirely.

author: ciccio
author_rank: Frequent Contributor
timestamp: September 24, 2020, 06:02:36 pm
content: I searched about this "Stetzerizer filter". In heir Website they quote about a study connecting an increase of Childs Leukemia due to increase of electrification.I truly believe that this type of advertysing is definitely "Criminal" - CompetentAuthorities must order for the products be recalled an destroyed.Newspaper mut do their job: ask for competent advice, then inform people correctly,

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2020, 06:06:17 pm
content: After reading the literature, I am still not seeing a use for it.http://www.gryphon-inc.com/PDF%20Literature/Power%20Probe%20-%20AC%20Line%20Viewer.pdf

author: oh_no
author_rank: Contributor
timestamp: September 24, 2020, 06:10:30 pm
content: Against the Tripp-lite, the product being promoted in the OP is here:https://www.powervar.com/products/power-conditioners/standard-power-conditionersThis is Powervar (Amtek)-- a major (serious) manuf. of products similar to Tripp-lite. Ironically, they are both based out of the Chicago area. Both the Amtek and Tripp-lite products are similar in $.As was suggest earlier in this thread, thead hocdiff. "line probe" may be a DIY device. For large manufs. like Amtek, they may have very-pro-lookingad hoctest gear for in-house use. That device in question has BNC-terminated cables coming out (what are plugged into 'scope) . That is not what is usually seen in std. industrial/consumer products -- diff. probes -- with std. probe leads.

author: Gyro
author_rank: Super Contributor
timestamp: September 24, 2020, 06:41:22 pm
content: It could be something as simple as a small isolated step-down transformer - toroidal for best HF response.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2020, 06:49:35 pm
content: You can lead a horse to water.....Do I need to read the datasheet for you next?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2020, 06:56:09 pm
content: Used one for $100.https://www.ebay.com/itm/Powervar-Power-Probe-115-Power-Tester-Manual-3-Cables-120-250-VAC-PP115-NEW/283992319384?hash=item421f42e598:g:jk8AAOSwfo1fSBZW

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2020, 06:58:08 pm
content: Now I understand. It's the audio guys who need it.https://www.diyaudio.com/forums/equipment-and-tools/226679-checking-dirty-power-scope-3.html

author: oh_no
author_rank: Contributor
timestamp: September 24, 2020, 10:39:56 pm
content: Quote from: joeqsmith on September 24, 2020, 06:56:09 pmQuote from: joeqsmith on September 24, 2020, 06:49:35 pmQuote from: joeqsmith on September 24, 2020, 06:06:17 pmQuote from: joeqsmith on September 24, 2020, 06:58:08 pmEither you are suicidally bored or you are being paid per post!

author: joeqsmith
author_rank: Super Contributor
timestamp: September 24, 2020, 10:43:46 pm
content: Quote from: oh_no on September 24, 2020, 10:39:56 pmOf course you missed the most important one:Quote from: joeqsmith on September 24, 2020, 06:06:17 pm

author: oh_no
author_rank: Contributor
timestamp: September 25, 2020, 03:29:19 pm
content: Quote from: joeqsmith on September 24, 2020, 10:43:46 pmYes. And that's mostly because of your non-stop yapping. Low signal to noise ratio leads to Cry Wolf.Yeah, that was the most useful reply in the thread. But you should've chased it down to the product page:https://www.gryphon-inc.net/product-page/power-probe-model-pp115Power Probe Model PP115$490.00Price

author: tooki
author_rank: Super Contributor
timestamp: September 25, 2020, 03:55:10 pm
content: Quote from: oh_no on September 23, 2020, 08:01:09 amYou chose to post in the Beginners forum. You provided no additional information on your background. The ONLY safe thing for us to do is to assume you are a beginner who doesn’t understand the safety ramifications, because if we assumed you did know, and you actually didn’t, it could LITERALLY kill someone.So you don’t get to be a miffed prick with a bruised ego because we didn’t bow down to you and your post.

author: tggzzz
author_rank: Super Contributor
timestamp: September 25, 2020, 06:19:29 pm
content: Quote from: oh_no on September 25, 2020, 03:29:19 pmNo. Your question and you want help => your responsibility.Read and re-read the previous post from Tooki.

author: oh_no
author_rank: Contributor
timestamp: September 25, 2020, 08:19:00 pm
content: Quote from: tooki on September 25, 2020, 03:55:10 pmNow how do you ASSume that? It is you who is getting upset ... hence your verbose, off-topic reply, which CLEARLY has no relevance to the OP .

author: oh_no
author_rank: Contributor
timestamp: September 25, 2020, 08:21:39 pm
content: Quote from: tggzzz on September 25, 2020, 06:19:29 pmI did better than that: I replied to it ...... see fer yerself, toots ................

author: tggzzz
author_rank: Super Contributor
timestamp: September 25, 2020, 09:15:43 pm
content: Quote from: oh_no on September 25, 2020, 08:21:39 pmNo. You wrote a (silly) response, not a reply.You are either a troll, have Dunning-Kruger syndrome, or are unable to comprehend how other people will understand what you have written (cf what you intended them to understand). But it doesn't matter which of those it is; you are a waste of my time.

author: oh_no
author_rank: Contributor
timestamp: September 26, 2020, 11:20:00 am
content: Quote from: tggzzz on September 25, 2020, 09:15:43 pmI had little bit of gas from my last salad.But the HILARITY ofy'all's replies(PLURAL) let a real juicy one rip ........... AHHHHHHHHHHHHHHHHHHHH!!And thanks!!!!!!!!!!!!

author: tooki
author_rank: Super Contributor
timestamp: September 26, 2020, 12:47:01 pm
content: Quote from: oh_no on September 25, 2020, 08:19:00 pmOh, I’m not assuming. You’ve proven it with your flippant, immature responses to everything.If you had two brain cells to rub together you’d understand our concerns. Unfortunately you’re right in that Dunning-Kruger trough of being juuuust dumb enough to think you’re a goddamned genius, while not actually understanding what we said.

author: tggzzz
author_rank: Super Contributor
timestamp: September 26, 2020, 01:05:27 pm
content: Quote from: tooki on September 26, 2020, 12:47:01 pmGiven his response, my money is on a troll. As with sulking kids, a useful remedy is "a good bit of ignoring".

author: oh_no
author_rank: Contributor
timestamp: September 26, 2020, 03:45:54 pm
content: Quote from: joeqsmith on September 26, 2020, 01:51:28 pmOh, uh, before you depart .... would you PUH-LEEEEZE mind 'splanin' you earlier remark:Quote"Thank you. Thank you very much."

author: oh_no
author_rank: Contributor
timestamp: September 26, 2020, 03:59:41 pm
content: Quote from: Brumby on September 23, 2020, 11:16:58 pmThe OP was posted in "Beginners" because (unlike most forums), there is no General sub-forum under the main ELECTRONICS forums. Earth calling Mods ... y'all might want to add a General Questions category. I gah-rawn-teee it'd become y'all's top hang out.QuoteY'all keep 'ferrin' to this Dunning–Kruger cowboy.... sorry ... too dumb fer dat citytalk ....I'm from Missouri,folks.

author: tooki
author_rank: Super Contributor
timestamp: September 27, 2020, 10:54:12 am
content: Quote from: oh_no on September 26, 2020, 03:59:41 pmOr if you were a bit more attentive, you’d have realized that your question (“can anyone identify this bit of test gear”) doesn’t belong in a general questions category, but in the existing “test equipment” forum. Before you lecture others, you’d be well advised to verify your own understanding first.Another tip: when you’re a greenhorn in a forum (which you are here), don’t go in with guns a-blazin’. It does NOT impress the locals. Learn the forums’s customs and etiquette before opening your mouth.

author: oh_no
author_rank: Contributor
timestamp: September 27, 2020, 09:51:55 pm
content: Quote from: tooki on September 27, 2020, 10:54:12 amHey cowboy, you must be REAL BORED and/or stoooooooooooooopid. Keep comin' back fer more. Hittin' us up fer 'nother fix.Yeah, Mr Corona's got a lot lotta boredom-relief joints shut down. Guess that 'splains things.

author: james_s
author_rank: Super Contributor
timestamp: September 28, 2020, 04:22:05 am
content: I haven't seen any of the mods in here yet but given past experience I'd say that you're about an inch from getting banned. People are trying to help you out and you're just getting worked up and being rude. Either calm down and be polite or kindly go somewhere else.

author: Simon
author_rank: Unknown
timestamp: September 28, 2020, 06:55:33 am
content: Ohi, we do metric around here, 1µm more like. Let's give him 7 days to cool down.