Cheap oscilloscope for checking mains power quality? Also logging equipment. - Page 1
Forum section: electronics / testgear

author: mrsparkle
author_rank: Newbie
timestamp: April 28, 2024, 12:29:44 pm
content: Hello,I am a residential electrician that occasionally has to troubleshoot issues such as LED flicker, GFI nuisance trips, and well that's about it. I am looking for a very basic oscilloscope or similar device that I can connect to the lines and check for noise / power quality issues. Mostly just to verify that X is the culprit, whether X is an ev charger or dirty power from the transformer.As such, I do not want to spend a lot, and I have a fairly limited usage, only to be able to check for a malformed voltage or current waveform at 120/240V. What's a good selection for me? How cheap can I go, and what are the minimal specs I should look for?Also, at times I may need to respond to an intermittent issue and attach a data logger inside a panel for a day or two that can pick up on rapid spikes or sags. Again, I would use this tool rarely and don't want to spend a lot. I know there are higher end loggers like Flukes, over $1k, which is more for industrial use, but its not nearly so critical to my job. Again, what would be minimum specs and price point for that?Thanks

author: artag
author_rank: Super Contributor
timestamp: April 28, 2024, 12:47:16 pm
content: I have no direct experience of using it for mains quality so take it with a pinch of salt, but I find distortion very hard to judge on an oscilloscope. Other problems such as transients are by definition occasional so won't show up unless you have the trigger just so.A general purpose piece of lab equipment that would be more suitable is a spectrum analyser. That seems like overkill but it only needs a low frequency response - maybe to the 5th harmonic of 60Hz to show distortion.But a spectrum analyser offers far too much to be used only for this and so is not normally used. There's a reason sapecific test equipment such as mains power analysers exist : it's customised to do the exact job and robust enough for field use. There are also scopes that are ruggedised for the job - such as the obsolete Tek 555PS - and have appropriately rated probes and inputs that are suitable for use on high power circuits (it's easy enough to measure voltage with respect to earth, not so easy with respect to neutral).My recommendation would be to look for a specialised unit but buy it secondhand.

author: Kean
author_rank: Unknown
timestamp: April 28, 2024, 01:51:54 pm
content: I don't think an oscilloscope is the best solution based on your usage. You want a power quality analyser with data logging. Something that can also safely be left alone.Maybe one of these.https://powertronics.com/collections/single-phase-power-line-monitorsSee these other related discussionshttps://www.eevblog.com/forum/testgear/power-line-quality-monitor-that-does-not-cost-/https://www.eevblog.com/forum/testgear/looking-for-a-cheap-but-good-single-phase-120v-power-line-glitch-logger/

author: adam4521
author_rank: Regular Contributor
timestamp: April 28, 2024, 09:41:23 pm
content: For low cost power quality logging I've had some success using a commercial-grade electricity meter: Schneider PM5110/PM5111 for example which you can easily find used/surplus. Install into an adaptable box. Lower cost than a power quality analyser, and you can read out voltage, current and harmonic data to a computer via Modbus RS485 interface. But this will be a bit of a do-it-yourself project.For RCBO/GFCI nuisance tripping, often this will be linked to a switching transition -- something being connected to the system or switched on, that creates a transient unbalanced current in the live and neutral conductors. For LED flicker, it's traditionally associated with unstable timing of 'phase cut' dimming: the lighting driver is interacting with the dimmer. If you really want to see what is going on you will want the oscilloscope, but you will need to convert the current signal you want to observe to a voltage signal. As electrician, you would be confident making up a circuit breakout box with a CT and suitable burden resistor inside? You might make a specific one for measuring residual current -- look for a 'zero sequence CT', which has higher sensitivity.Multiple times on the forum we discuss safe connection of oscilloscope to mains. The current transformer appropriately terminated will be ok. Differential voltage probes are great (but relatively expensive, unless you land one second-hand). You can use a voltage transformer to keep voltage measurement simple, but won't be super-accurate for observing some of the transient events. Battery powered oscilloscopes from Fluke are purpose-made, but they are really expensive, even for really old ones.

author: csuhi17
author_rank: Frequent Contributor
timestamp: April 29, 2024, 07:02:25 am
content: The oscilloscope can only be used for one phase, you will not be able to use Pass/Fail for several phases at the same time. It can only be set to one channel.It is worth using a differential measuring probe to monitor the voltage, you will need a current measuring probe to measure the current.The battery does not last long, a few hours max.I found three options when I did this myself.1. You buy a power meter with a bluetooth connection, which you can connect to an Android device and use it to log in at some level.2. buy two Bluetooth multimeters and/or lock pickers, one for current, the other for voltage, which you also connect to a phone, if you're lucky, you can set the logging interval in its software.3. buy a cheaper energy quality meter.3.1 I found one that can be connected directly, but it has an RS485 connection, I didn't check what it can do.I couldn't find much information about it.3.1 There is the ME435 Meter, which is an independent item, for approx.: 400-500 USD. ETCR4320, ETCR4300 that I still found.3.2 borrow one for that little time. If you need to use it a lot, it is cheaper to buy one, if you only need it now, then borrow one.The scope has a high sampling rate, you can slow it down, but then you need one with a lot of memory, otherwise you won't be able to set it properly. And it's even more expensive because of the extra accessories.The consumption meters are cheaper, but the sampling is slower, which I use 1 sample per second.The multimeter is a little faster, 3 samples/second, and you can use it for other things later.If everything is true, the ME435 works with 8000 samples/second.For me, the end result was the Atorch AT4PB consumption meter, connected to the Unihertz Tank phone, very long operating time. Only the bluetooth version. In any case, not the TUYA and similar WiFi nonsense...And two Owon CM2100B.For these, there is still work to be done to evaluate the result.The Schneider PM5110 mentioned by Adam4521 is 64 samples per second if I see correctly.

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2024, 10:03:38 am
content: Quote from: mrsparkle on April 28, 2024, 12:29:44 pmWelcome to the forum.If 2 channels are enough and you understand the risks of ground loops then SHS810X might be a solution to your requirements.https://siglentna.com/handheld-oscilloscopes/shs800x-series/

author: Phil1977
author_rank: Frequent Contributor
timestamp: April 29, 2024, 04:18:44 pm
content: For finding EMI misbehaviour I can really recommend such a TinySA spectrum analyzer together with an inductivce probe.By "scanning" your devices with the inductive probe you - contactless! - find the characterstic emission of e.g. SMPS or LED drivers. If you trace down the power supply line with the inductive probe and clearly see one of the contributors, then chances are high you have found the bad guy.Big advantage of using an inductive probe (e.g. just a 5uH ferrite inductor soldered to a SMA-cable) is that *usually* the coupling for dangerous signal components (DC or 50Hz) is so bad that nothing happens to you or to the SA - at least as long as you slowly approach your subjects.Probably you would even get along with the non-official TinySA-Clones for this purpose, but the "real" TinySA is so valuable and the price difference is not that much that I would principly take a real one.

author: adam4521
author_rank: Regular Contributor
timestamp: April 30, 2024, 09:22:28 pm
content: Quote from: csuhi17 on April 29, 2024, 07:02:25 am64 samples per cycle. But only for internal processing. You can’t read out individual samples.

author: pdenisowski
author_rank: Super Contributor
timestamp: May 01, 2024, 06:12:20 am
content: Quote from: Kean on April 28, 2024, 01:51:54 pmI completely agree with this. We (R&S) manufacture both portable oscilloscopes and power analyzers, and I would personally choose a power analyzer for what you are describing.If you do use a scope, it should have some kind of power analysis application or function, e.g. something that will provide things like power factor, harmonics / THD, etc. And many scopes don't natively have a logging function.You also need to consider how you will connect to the AC mains: you will probably need a differential probe and/or some kind of breakout box if you want to use a scope. Power analyzers often have an AC mains adapter that doesn't require a differential probe (see attached photos)Probably (well) outside of your budget, but to give you an idea of what power analyzers do:https://www.rohde-schwarz.com/us/products/test-and-measurement/rs-essentials-meters-and-analyzers/rs-npa-power-analyzer_334255.html