Electronics > Beginners

Oscilloscope for AC work ?

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plurn:

--- Quote from: SND on May 03, 2019, 08:02:18 pm ---The battery scopes like the siglent 810 and hantek's don't see to get the best reviews and I have no use for their multi-meter side. A fluke 125b could be nice for at almost $4k, hard to justify for this.

--- End quote ---

If you are on a budget, the siglent SHS1000 series would probably be more appropriate than the siglent 810 (SHS810 - SHS800 series). They seem to be very similar operationally, though the SHS1000 series has isolated channels with "Oscilloscope isolation level: CAT II 1000 V and CAT III 600 V" (this rating seems to be when using suitable 10X probes). SHS1000 costs more than SHS800 series, but a lot cheaper than the fluke equivalent, or most dedicated power analysers.

From the images here https://www.siglentamerica.com/handheld-oscilloscopes/shs1000-series-isolated-handheld-digital-oscilloscopes/ it seems to have FFT but I don't see a THD calculation there. If you don't need accurate THD calculation perhaps you could roughly work it out relatively easily from the dB levels of the fundamental and biggest harmonic on the FFT display using an online calculator or a table:

http://www.sengpielaudio.com/calculator-thd.htm

For example, if the fundamental is at -10dB and the biggest(loudest) harmonic is -50dB, the difference is 40dB. Then "Distortion attenuation a" = -40dB. Put -40 into the calculator and that gives THD% of 1%

Or just print out the "Table: Distortions and the dB and percent and the decibel" on that page and do a quick conversion. Probably easy enough to memorise too.

Depending on your business needs that might be close enough? Doubt you need THD% to 3 decimal places or anything but that is for you to determine. Perhaps you just need >5% is bad, <5% is good?

I am not an electrical engineer or anything so no idea if that is an effective or correct way of determining THD%. It is quick and easy though.

One other option though I don't think it fits your requirements, the Keysight U1242C multimeter (not an oscilloscope) measures/calculates something it calls "Harmonic Ratio" based on measuring RMS AC, and average responding AC. Details here: http://literature.cdn.keysight.com/litweb/pdf/5989-7687EN.pdf

Not sure if the AC bandwidth of the U1242C is sufficient? Doubt it goes up to 5kHz.

joeqsmith:
If you are on a budget, you may want to look at a used one.   I've used one of these and they are pretty nice.  The problem is that they are no longer supported by HIOKI.  You can still get batteries but if anything were to get damaged, they will no longer service them.   

https://www.ebay.com/itm/HIOKI-3196-POWER-QUALITY-ANALYZER/183792935792?epid=1501714264&hash=item2acae9a370:g:JwgAAOSwCtJcx4Zp

plurn:
found this - UNI-T UT283A Single Phase Power Quality Analyzer Energy meter

relatively cheap. Seems to have THD%. Don't know if it is any good or safe.

edit:
Harmonic analysis:   Up to 51th

Does that mean eg 60Hz fundamental * 51 = 3060Hz ? So might not show the 5kHz+ that you need.



http://www.uni-trend.com/html/product/General_Meters/Power_Quality_Analyzer/UT283_Series/UT283A.html

joeqsmith:
Normally if I am doing this sort of work, an typical oscilloscope I would use for electronics would be useless.  The first problem is I not only need the equipment to survive in the field, I need it to capture some potentially large events (transients).   I normally need both current and voltage.   Complex triggers are a must.    I also want long term recording of the events and the ability to post process them.   

When I was first looking for one of these, HIOKI (and others) had brought in demo units.  I ran transient tests on their demo units (with the approval of the sales men).   Not the little toy generators I use to benchmark the handheld meters, but the real deal.   

I like the new HIOKI units.  Cost is about $10K USD but well worth it if you need this sort of tool.   I've used them to solve some pretty odd problems. 

Then again, if the goal is just to look at the AC line voltage at one of your home's outputs for the sake of looking at it, this would be a total waste. 

plurn:

--- Quote from: SND on May 04, 2019, 11:41:24 am ---Thanks for all the replies.
I'm currently considering the AEMC 407 clamp meter, with their free bluetooth software it might get me close enough to what I'm trying to find, at least it has some THD functions. I'm not 100% sure it'll get to the higher frequencies that might be in there but for a bit over $500 could be worth a try.

--- End quote ---

AEMC 407 clamp meter does "Individual Harmonics (to 25th)", so I would think that means 60Hz x 25 = 1500Hz only? So probably won't show 5kHz.
https://www.aemc.com/userfiles/files/resources/datasheets/Clamp-On-Meter/2139-51.pdf

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