How to check AC 120 volt mains lagging problem with Rigol DS1054Z ? - Page 1
Forum section: electronics / testgear

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 06:55:52 am
content: HiIn the 70's I exploded a scope probe by looking at AC mains, so I am gun shy.I am having AC lag voltage, ie sometimes my lights flash (go out). I want to use the Rigol's "envelope" feature (not sure of the correct term). The Rigol is able to set up an over voltage and under voltage setting, that will trigger a capture of the waveform (I think). Thus determining the minimum AC voltage.This problem happens more in the winter than the summer (I think it is a moisture problem). I want to put together a case to submit to my utility company proving it is the transformer at the pole, if I can prove it is moisture related. The pole is very hard to get to so I know they will not want to check it and I expect them to tell me to hire an electrician.I bought this to usehttp://www.ebay.com/itm/110V-to-12V-60W-Light-Power-Supply-Converter-Electronic-Transformer-Black-TS-/172255252160?hash=item281b368ec0:g:PHEAAOSwOVpXcP46I think the first thing to worry about is can I trust this? What would be some test procedures to test it first? Set a resistor to run it at 60 watts? I have two to test.Does anyone know of any YT videos of the Rigol's feature to do this (I do not know the correct term)? Or has anyone done this? I apologize for asking this but I am really afraid of blowing up my Rigol (and killing myself). So if there are any Rigol protector fans out there, I would really appreciate the help in avoiding blowing up my Rigol.FYI - I do not have an isolation transformer (I guess I could get one). I have 2 wire AC, ie no ground (thus the difficultly getting an isolation transformer). I live in a house that is over 100 years old. I could do this experiment in the kitchen, which is the only room with a ground if needed.I may need to run this experiment for at least 6 months, so I got to get it right.On the output of the transformer, I think I could use a 100 ohm resistor and connect the Rigol's leads across it. So the watts will be 1 watt, so it should not over stress the transformer.Is there any kind of protection in front or back of the transformer that I can use? I will be using this continuously for about 6 months.If this experiment is successful, I think this will save me more than the cost of the Rigol. If not, I blow up the Rigol or burn my house down. So any help is greatly appreciated.Thank you

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2016, 10:32:34 am
content: That little ebay "electronic transformer" is probably a switch-mode power supply, useless for your task. Just order a simple transformer that goes from 120V to 12V on the secondary, like this:http://www.digikey.com/product-detail/en/triad-magnetics/TCT3-03E07AE/237-1602-ND/3995756That not only brings the voltage down to something easy to work with, it also provides full isolation so you won't fry your scope. And the 10:1 ratio makes it easy to perform calculations on the results. Just be sure to wire and house it carefully in an insulated enclosure.With all that said, there are power monitoring devices sold specifically for this purpose. It might just make sense to rent one of those for a while and see what it figures out.

author: macboy
author_rank: Super Contributor
timestamp: August 16, 2016, 12:51:51 pm
content: tooki is right, you need a wall-wart type transformer with an AC output, 12 VAC for example (current does not matter). Note that AC output transformers are much less common than DC output, but AC is what you need to monitor to the waveform. There is no need to load the output but you can put a very light load on it (like 1 k ohm) if you wish. Just connect the 12 VAC to the scope input directly or through a probe, it doesn't matter, it is low voltage, low energy, and transformer isolated (floating) so it is safe.

author: alanb
author_rank: Frequent Contributor
timestamp: August 16, 2016, 01:06:00 pm
content: The oscilloscope may not be the best tool for the job. You could use a multimeter that has a remote logging output to log the voltage at intervals of a few seconds. Log to a PC with the time of day.

author: madires
author_rank: Super Contributor
timestamp: August 16, 2016, 01:09:38 pm
content: I'd recommend to get proper differential probes for your scope. A transformer might be a simple solution, but it's also a filter. There are several IoT mains/power monitors, which could be a more efficient way to track mains on the long term.

author: Fungus
author_rank: Super Contributor
timestamp: August 16, 2016, 01:12:55 pm
content: Quote from: alanb on August 16, 2016, 01:06:00 pmThis.(but log as many readings as possible - you can always throw data away later)

author: Seekonk
author_rank: Super Contributor
timestamp: August 16, 2016, 03:02:22 pm
content: An AC waveform will always have a minimum value of 0.00. I would full wave rectify a AC transformer with a load resistor and a capacitor to form a short time constant. That will produce a DC signal that is a little choppy on top but good enough that a scope could trigger on a voltage sag.

author: rstofer
author_rank: Super Contributor
timestamp: August 16, 2016, 03:36:27 pm
content: Since you are probably looking for transients, logging of averages is useless. The proper tool is known as a "Power Disturbance Analyzer" and it is designed specifically to catch transients. We used them extensively in the 'mainframe era'.Maybe do a little research on the tool and see if there is something that can be built by a DIYer.Dranetz is a popular brand and there are quite a few on eBay. Whether they work or not is a separate problem.

author: Fungus
author_rank: Super Contributor
timestamp: August 16, 2016, 04:02:17 pm
content: If you actually own a Rigol DS1054Z instead of a "Rigol DZ105Z" then youcanuse it directly on the mains.CAREFULLY.a) Make sure the probe switch is in the "10x" position.b) Put the 'scope in A/C mode. It's the first item in the right-hand menu after you press a channel select button.c) Connect only the probe's main hook to a wire, do NOT connect the ground clip to anything - that's what blows 'scopes up!d) In fact: Completely remove the ground clip from the probe before you start. They detach if you pull theme) If you're not seeing 120V AC on screen then try connecting the probe to the other wire.Now set up the runt trigger options and watch it count.Disclaimer: You're messing with dangerous stuff. Failure to doanyof the above can release magic smoke from the 'scope and/or fusebox and/or you. Everybody reading this post is screaming at me right now saying, "don't do it!"PS: The oscilloscope won't tell youwhat timethe problems happened or log the min/max values - and that's the information the electric company probably wants to know!

author: alanb
author_rank: Frequent Contributor
timestamp: August 16, 2016, 04:05:23 pm
content: Quote from: Seekonk on August 16, 2016, 03:02:22 pmIn my suggestion to use a logging multi meter I was assuming that the RMS value would be logged not DC.

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 08:41:16 pm
content: Quote from: tooki on August 16, 2016, 10:32:34 amWhat a surprise - I did not even know what an "electronic transformer" is, I thought it was Chinese English. So I opened it up and there are diodes, caps, transistors, etc. What is this? Why not just a coil? I guess this is cheaper, ie smaller coil. Does anyone know where I could find a circuit diagram? Attached are pictures of this silly thing.Unless these things have a use, they are going to the trash. And I am going to order thishttp://www.digikey.com/product-detail/en/triad-magnetics/TCT3-03E07AE/237-1602-ND/3995756FYI An AC wall wart is too hard to find.thanks tooki

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 08:46:28 pm
content: Quote from: alanb on August 16, 2016, 01:06:00 pmI bought an Owon meter for less than $40 that will data logging 5 x second to an Android (really cool) BUT after I got it, I realized I am looking for an event that takes place probably in 1/60 th of a second (I have 60hz). I bet I could not even find one event in a year. My "blinking" occurs from none to a dozen a day. Current maybe 2 a day.So this will not work.thanks for the idea

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 08:51:21 pm
content: Quote from: Seekonk on August 16, 2016, 03:02:22 pmInteresting idea. If I cannot get the Rigol to do an "envelope" test, I will try this. I am pretty sure it can, I once saw a video about this, but I cannot find it now. Now I have to wait and get another transformer that tooki told me about.Thanks

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 08:56:38 pm
content: Quote from: rstofer on August 16, 2016, 03:36:27 pmGreatIt is good to know the name of the tool. So if my method does not work, I will see if I can get one of these off of ebay. But I am going to start looking now just in case and learn what they can do.

author: ez24
author_rank: Super Contributor
timestamp: August 16, 2016, 09:10:48 pm
content: Quote from: Fungus on August 16, 2016, 04:02:17 pmRigol DZ105ZI corrected the titleI think I am going to try this before I order a transformer. You are right about the ground clip so I feel better by removing it. Thanks for the term "runt", I did not know what to call it.Too bad about the time thing, I did not know this. But I found out I can "see" the lags a lot better if I use a light with a dimmer on it and turned down as much as possible. This way I can make a note of the time.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: August 17, 2016, 03:41:47 am
content: Quote from: ez24 on August 16, 2016, 08:51:21 pmThe Rigol has the Pass/Fail option under the Utility menu. This allows you to set a mask (what you are calling envelope) around the displayed waveform. You can fiddle with the controls to make the mask tight or loose around the waveform, and choose to have the scope stop when the mask limits are met. But the problem is that it halts the scope to capture the signal that _exceeds_ the mask shape, which is opposite to what you need to capture voltages that sag or become smaller.The runt trigger option will allow you to _trigger_ the scope when the voltage drops, and if you put the scope in Single-shot mode the scope stops once it has triggered, so the waveform will be captured on the screen. It takes some practice to get the hang of using the runt trigger and the Single mode. Again, without a timestamp. You could put a clock next to the scope and video the event with a webcam...There is also no timestamp available with the 1954z, because it has no internal real-time clock.

author: Fungus
author_rank: Super Contributor
timestamp: August 17, 2016, 05:34:50 am
content: Quote from: alsetalokin4017 on August 17, 2016, 03:41:47 amThere's mask underneath the wave as well as above it.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: August 17, 2016, 09:25:35 pm
content: Quote from: Fungus on August 17, 2016, 05:34:50 amYes, that's true. I don't know what I was thinking, thanks. I actually use the mask function, too, so I'll just have to admit to having a late-night brainglitch.Here's a screenshot where I set up a mask on an AC signal at high amplitude, then reduced the amplitude to trigger the "fail" state.

author: ez24
author_rank: Super Contributor
timestamp: August 17, 2016, 11:41:44 pm
content: Quote from: alsetalokin4017 on August 17, 2016, 09:25:35 pmThanks - the screen shot helps a lot.Just ordered thishttps://www.amazon.com/Class-II-Transformer-Approved-MGT-1220/dp/B002LG8008/ref=sr_1_1?s=aht&ie=UTF8&qid=1471476220&sr=8-1&keywords=Class+II+Transformer+-+12+Volt+AC%2C+20+VA%2C+UL%2FCSA+Approved+%3A+MGT-1220because I wanted another item on amazon to meet the $49 min order.I am 99% sure this is a transformerI will put the 12 VAC across a 1k resistor and put the scope leads across the resistor. If and when I get this working I will post a picture of it.I just cannot hook up to 110 AC, I had a near death experience that has put the fear of god (Dave this is not a religious topic ) into me.So when I get the transformer, I will connect it according to the screen shoot that alsetalokin4017 showed me.Thanks everyone, it has been really helpful

author: alsetalokin4017
author_rank: Super Contributor
timestamp: August 18, 2016, 02:35:32 am
content: You're welcome.Just make sure the resistor you use can handle the power.