Masuring AC lines Vs power conditioned lines using analog scope SAFELY! - Page 1
Forum section: electronics / beginners

author: Beamin
author_rank: Super Contributor
timestamp: September 16, 2018, 07:12:02 pm
content: I have a furman AC215 and a tek 2465 scope where I want to see if the power conditioner actually smooths out the mains sine wave. It’s sold to make high end hifi sound better(sounds like bullshit since a high end amp should already have a clean power supply but this could make a difference if you had bad 3rd world electricity or a generator). I’m not sure if the furman isolates the output; it has a three prong but but not sure if the neutral are all tied together) it has a huge toroid in it with what looks like a 1:1 transformer. I have generic probes for the scope. So somethings to keep in mind: the ground on the scope is tied to the neutral line. If you are not isolated this becomes a problem or is this a problem only on old radios (saw it on a MRCarlson video, where he explains if you have a non polarized plug you could accidentally create a short with your scopes ground). Do I have to build a circuit to stop the scope from just becoming a short with the full mains current running through the scope? The probes are 10/100X I believe, they are the standard generic 100Mhz ones you get for $20 off ebay. The scope has a 50 ohms setting, this isn’t just resistance but something for radios: or if I pick that hook up hot and neutral and 15amps will flow through 50 ohms blowing up the scope? Are scopes like multimeters with very high impedance? I would imagine this would be bad for measuring small signals like logic level. Should I build a circuit that AC couples it some how? What would be required to do it safely? How do I keep out other 60Hz buzz from getting onto the signal? I have played with this scope a few times trying to get oscillators to work and many times picked up the 60hz buzz thinking it was the signal...

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 16, 2018, 08:07:50 pm
content: Um... ah.... er..... STOP!Have you watched Dave's video on how not to blow up your scope? You absolutely MUST watch and FULLY UNDERSTAND this video before you turn on your oscilloscope again. This is a safety issue of the greatest importance. You can not only destroy your oscilloscope but you can KILL YOURSELF if you don't do this stuff properly and safely.Sorry for shouting but there seems to be some difficulty with this communication channel.Your post reveals that you do not understand:Probe attenuationInput impedanceAC couplingGroundingand a lot of other basic stuff that most of us take for granted.So STOP! and don't even THINK about trying to scope the mains or anything mains-connected like your "power conditioner" until you have watched Dave's video as many times as necessary and have also absorbed all the underlying concepts.I will not answer each of your questions in the post above directly because they are kind of like asking a cook "why do you put flour in a cake mix". If you don't already know... you don't belong in the kitchen. Yet....

author: taydin
author_rank: Frequent Contributor
timestamp: September 16, 2018, 08:19:34 pm
content: You can use one of the following methods:- Power the device (Furman) from an isolation transformer.- Use a differential probe instead of the existing 10/100 probes.She didn't strike me as clueless as the first responder made it look to be. But in any case if you have no idea what the above means, then by all means, watch Dave's video.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 16, 2018, 08:40:47 pm
content: Quote1. I'll bet a cheezburger those probes are actually 1x/10x.2. Read that "50 ohms" part again and let it sink in.Watch Dave's video, or not? Go completely through the beginner's oscilloscope thread, or not? Review basic concepts of electricity... or not? It's up to you, I disavow all responsibility, this post will not self destruct in five seconds.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 16, 2018, 08:41:04 pm
content: I wonder if you would be better off reverse engineering it, then run it on SPICE. If you wanted to see how it works on a real AC line, you need some way to perturb the input signal. It may not be such a simple job to do in real life compared with using a simulator.

author: Zero999
author_rank: Super Contributor
timestamp: September 16, 2018, 08:43:41 pm
content: My advice would be to open it up to see what's inside, before even thinking about 'scoping the output. It's possible the mains is already clean enough where you live, that there wouldn't be much difference any way. By reverse engineering it, you can figure out whether this device will actually make any difference or not. No doubt other, much safer tests which can be done, to see if it works, without connecting it up to the mains and connecting a 'scope to the output. For example, connecting a signal generator to the input and a load resistor to the output, sweeping the signal generator from the mains frequency, up to a few MHz and 'scoping the output, will tell you how well it filters RF, without having to worry about dangerous voltages.When ever something is marketed at improving audio, it always makes me feel more cynical. Mains power filtering is very real and a very noisy supply can cause problems with audio. as well as other equipment, but most of the time it shouldn't be a problem. I'd be more inclined to buy a decent brand mains EMI filter and put it in a box with sockets and a mains cable, rather than buying anything like this, which could just as easily be overpriced rubbish as a decent product. However, I'll remain open minded about this device, until I've seen the insides or the results of prpper tests.

author: rx8pilot
author_rank: Super Contributor
timestamp: September 16, 2018, 08:59:26 pm
content: These are pretty useful for this type of work.....although you have to cough up a few pony's for them. An isolation transformer is a minimum foundational piece of gear that reduces risk when used appropriately.http://www.testequipmentdepot.com/bk-precision/pdf/pr2000.pdfIn general, measuring and analyzing line AC is a high-risk endeavor if you are 'learning as you go'. Blowing up equipment is the best case scenario. Blowing off a finger, arc flashes, fire are the next level scenario. The final scenario - is you get line voltage on opposite hands and your heart stops.Clearly, small mistakes create severe consequences.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 16, 2018, 09:01:40 pm
content: It looks like you're not totally sure what to do but asking for advice was a good first step. I think most of these claims about a plug, special wire, or other component making an amp sound so much better only benefits the seller and not the buyer. That being said, this device doesn't look like it would do any harm IF used correctly but you aren't going to see any real improvement in sound quality, but it is probably much better than the protection in your average outlet strip.As to how to measure line voltage with a scope, this is an art as well as requiring a good grasp on electronic fundamentals and isn't something you should try unless you really know what you're doing. There can appear to be interference and crud that really isn't there.This may not be the best way but the safest way is to use two low voltage transformers that will isolate the two high voltage points you are trying to measure as well as preventing ground loops and other problems. Put a plug on the primary and connect the scope probe to the low voltage secondary. Any transformer with 6 to 24 volt output should work. To measure 2 points would require 2 transformers and it would be good to get identical ones to make sure they react exactly the same. It is true that transformers do attenuate higher frequency signals but they are cheaper than differential probes.The last thing you want to do (and generally the first thing beginners think of) is to remove grounds, use an isolation transformer, or disable other safety features that has been put there for very good reasons. The question to ask is; if a feature has been incorporated into the equipment that you bought because it was built by such great audio and electrical engineers, don't you think they would have thought of it first?

author: Brumby
author_rank: Unknown
timestamp: September 16, 2018, 11:35:07 pm
content: It is clear you havesomeunderstanding - but it is also clear you do not have sufficient to handle probing around mains voltagessafely.The reasonalsetalokin4017took such a strong stance is that without agoodunderstanding of the risks and considerations involved ... you could kill yourself. Yes, I did mean to be that blunt. Of course you may only blow up something.You are to be commended for having the good sense to ask for guidance.I have been playing around with electronics since I was 8 and two years ago I had a problem with an item that strongly suggested scoping a power bus at mains potential. I thought about it. I bought a couple of 100x probes. I thought some more about it ... and worked an alternate approach that involved working through the circuit while it was completely unpowered. It took a bit longer and I had to turn the wick up on the old grey matter, but I worked out a solution. The extra effort was worth it as I knew I was safe - and that felt good.If youreallywant to scope mains potentials, I would strongly suggest the best approach would be to use some suitably rated differential probes. They aren't the cheapest set of probes you will buy, but they make mains measurements easier to perform safely. While there are other suggestions that can work, the differential probes would be my preferred approach.

author: rx8pilot
author_rank: Super Contributor
timestamp: September 16, 2018, 11:54:08 pm
content: Quote from: Brumby on September 16, 2018, 11:35:07 pmI was about 8 years old as well when I started building kits which stimulated my interest in electronics. That was 36 years ago. I have installed industrial electric, owned an industrial generator rental business, and dealt with 480v 3ph daily for about a decade. It still scares me - even 120v outlets. Perhaps the fear is constructive because I am still alive. Fortunately, the majority of my daily life now is 30VDC and lower.OP - stay safe. I hope that you were able to see that you really need to purchase appropriate probes and an isolation transformer. Even then, it only takes the tiniest error to create a situation that is best viewed on Electro Boom You Tube channel.

author: Brumby
author_rank: Unknown
timestamp: September 17, 2018, 12:09:19 am
content: Quote from: rx8pilot on September 16, 2018, 11:54:08 pmThat is respect. The second you do not respect electricity - bad things can happen.QuoteFunny. So does mine.

author: rsjsouza
author_rank: Super Contributor
timestamp: September 17, 2018, 12:26:16 am
content: A photograph of the innards of a similar model indicate to me it is an actual isolated switching power supply:(photo obtained fromhere)(edit) found adatasheetwith the same model and with an inside picture as well - almost identical to the one above.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 17, 2018, 03:06:26 pm
content: If you look at the photo of the innards of this type of device shown in reply #11, I will explain what I think it does after reading the spec sheet. It has all grounds carried through to the outlet ground prongs and does not isolate the output power lines, which I would consider a waste.First the power cord is connected at the lower right in the photo then goes through a double pole switch that can disconnect both sides of the line, then through the circuit breaker to the circuit in the upper right corner of the unit. This section has voltage sensing components that control the black cased relay with the number ‘2’ on it. If the average input voltage goes too high (also maybe too low) the relay will disconnect the output to protect your equipment. This circuit does not react to spikes but to a slower average increase or decrease in the line voltage, probably over a second or so.From the relay the power goes through a small silver colored 2-lead device on ceramic spacers that is a thermal fuse that opens if the unit overheats for any reason. To the immediate left of that thermal fuse is a blue surge limiting non-linear resistor to limit inrush current.Next the line goes through a toroidal inductor that will act as a high impedance to spikes on the line. The output lead from the inductor goes to a full wave bridge rectifier connected across the line with an electrolytic capacitor across the output side of the bridge and there is a brown bleeder resistor on ceramic spacers that is wired across the electrolytic capacitor. While it may not immediately make sense to have this bridge/cap circuit across the power, here is the theory. The inductor, already mentioned, acts as a high impedance to spikes while the capacitor on the output of the bridge acts as an extremely low impedance to spikes thus effectively eliminating any spikes from the output. The brown bleeder resistor discharges the capacitor slowly so its voltage will follow the average value of the line voltage. This inductor is different than the common mode dual inductors you normally see in filters used in switching mode power supplies and is possibly more effective.You could tell looking at the size of the unit that there was no way there was an isolation transformer inside. If my explanation of what the unit does is correct, it will pretty much do what it claims to do and for the price isn’t that bad. I wouldn’t try to go probing around inside with a scope without the required knowledge and a good reason.