Oscilloscope and power analyzers?
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  1. #1
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    Default Oscilloscope and power analyzers?

    Do you guys have any recommendations for a decent but not super expensive way to test the harmonics and wave form on the input lines from the PP?
    Seems all the real power analyzers start at $2000 and go up fast to over $10k. More than I want to throw at it.
    Would the cheaper $200 to $300 1 or 2 channel handheld oscilloscopes be any good for this?

    thanks

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    As far as I know oscilloscopes need special probes to read large voltages or you need to take a feed and reduce the voltage to read it using an oscilloscope.

    I wanted to do the same thing i looked and just walked away shaking my head not wanting the angry pixies loose on my equipment or me, I am told once the magic smoke is released it's impossible to get it back in.

    This is a video of what you want - there is no telling how it's done I am sure some of the smart peeps here could explain or give a diagram on how to do this
    YouTube

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    Rent what you need:
    Rent Test Equipment | Buy Test Equipment | ATEC Rentals
    Test Equipment Rental, Test Equipment Lease - TestEquity
    Which standards are you going to test to, and what are you going to do with the information once you have it?

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    If you want to test the harmonics at the INPUT side of the unit, it will either be line-to-line
    or line to ground. Both those measurements might be interesting.

    In the first case you will need a two input scope with the ability to difference the two input
    signals. Second case really only a single input scope.

    Because the peak voltages (what the scope actually displays) will be quite high, a 10X probe
    is not sufficient. You will need at least a 100X probe for most scope inputs which are
    typically 10 or 20 volt full scale.

    I suggest at least a 100 MHz bandwith unit, preferrably 500 MHz or even 1 GHz to see what's
    reallly going on there.

    Standard disclamer: voltages ARE lethal in the areas you will be poking around it. If you don't
    know what you are doing, maybe don't.

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    A power analyzer has 4 voltage connection probes and 3 current sensors. It will have some scope like functionality. I wouldn't bother with a standard scope. Define what you want to know before you start buying/renting and measuring, I can guide you along.

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    I use a Tektronics 453 that is considered ancient but it works as well now as it did when new. I do have to be careful about grounds. You don't need a super wideband scope for 60 cycle work. The harmonics are mostly multiples of 60 and most are well within the range of almost any scope. I have used the 453 in the last few days, first looking at RS232 spurious signals and then on the waveform of a saturable reactor used to limit current in a mag base drill.

    There are countless oscilloscopes, both CRT and handheld on EBAY at low prices.

    Bill

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    You really need current probes to get a good sense of what is going on.

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    "...test the harmonics and wave form on the input lines from the PP? "

    Current probes not needed. Frequencies are a LOT higher than 60 cycles.

    Excuse me. Hertz.

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    As noted, define what you want to measure and what you want to use the information for before proceeding. Are you looking just for power factor type stuff or harmonic distortion and Fourier analysis? Do you want to be able to record the data and do a computer analysis? Then there are spectrum analyzers.

    Using conventional lab type o-scopes on power lines can be dangerous. There are special scopes and plugins that are differential and isolated from ground. Another approach is to use instrument transformers for both current and voltage.

    If you want phase angles you will need at least a four channel scope (I don't know of a 3 channel).

    Tom

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    Quote Originally Posted by jim rozen View Post
    "...test the harmonics and wave form on the input lines from the PP? "

    Current probes not needed. Frequencies are a LOT higher than 60 cycles.

    Excuse me. Hertz.
    You have just identified yourself as being an OF(old fart).

    Tom

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    In the 'old days' (1980's-1990's) you would use a Hewlett Packard harmonic analyzer to show the harmonics in the waveform. Norma power analyzers (bought out by Fluke) now do the same function plus high accuracy power measurements, which was their original forté. I've used both in the field but as you say, they come under the 'super expensive' category. There are digital oscilloscope modules for adding to a PC that have FFT software add-ons readily available via ebay and amazon. Have a look around to see what you need.

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    Quote Originally Posted by jim rozen View Post
    "...test the harmonics and wave form on the input lines from the PP? "

    Current probes not needed. Frequencies are a LOT higher than 60 cycles.

    Excuse me. Hertz.
    They are cycles, kilocycles and megacycles, etc. Just as there is only one "The War".

    Bill

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    Quote Originally Posted by jim rozen View Post
    "...test the harmonics and wave form on the input lines from the PP? "

    Current probes not needed. Frequencies are a LOT higher than 60 cycles.

    Excuse me. Hertz.


    If he wants "harmonics", the frequencies will not be that high, and most any decent 'scope would show them.

    The real problem is that a 'scope does not give much info about harmonics. Some digital scopes will.

    Also, scopes such as the 453 are not isolated, so they are a good bit more trouble to use off-ground. using differentially helps, but the probes have to be adjusted very well or the results will be way off. Some of the digital scope will also have inputs that are isolated from ground and each other by something from 600 to 1200 volts, which is what you want. There you may be able to clip one suitable prove right across the power line.... check specs before you do that though.

    A power analyzer, such as Fluke and others produce, will be better suited to the job

    If he wants EMI range info regarding some product or piece of equipment, then using a LISN (line impedance stabilizing Network", with suitable spectrum analyzer, would be appropriate. But that does not seem to be what he really wants.

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    Been reading a bit more, mostly looking at figuring out Total harmonic distortion, and which hz are the worst, and ideally the strength of it?
    One reason being to regularly monitor the filter caps performance and catch it if and when THD starts to rise (I assume it should?)
    Other, if I start adding anything else for more filtering like a line reactor or other caps, I'd like to see if it is making a difference and where.
    I'm kind of assuming THD it probably a common basic calculation for most oscilloscopes but can't seem to find it mentioned in much specs so far.

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    Quote Originally Posted by TDegenhart View Post

    If you want phase angles you will need at least a four channel scope (I don't know of a 3 channel).

    Tom
    I do it all the time with one or two channels. For one, put it on the reference trace using the external trigger, not the signal to control the sweep. Adjust the sweep and trigger to display one sine wave with the beginning, center and end zero crossings right on the marks, then move the probe to the other signal and count marks.

    Bill

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    I've picked up a few scopes on ebay, I have a dual trace and quad by Tektronics, Also have a Dual beam Tek., has 2 guns not chopped trace. But my favorite is an Hitachi (think I spelled it right) quad trace really nice scope made in Japan. Input voltage is higher than Tek. scopes, if my memory is correct 400VAC. Also picked up quite a few plug-ins and high voltage probe. Check ebay they might have just what's needed.

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    I can't tell where the OP is located within Canada (remote, suburban???) but if anywhere near population centers, if you can find a location and date for any sort of substantial sized 'hamfest' (amateur radio flea market/ swap meet) or even get connected with a network of hams, older, nicer CRT scopes sometimes go for prices approaching 'free if you take it.' I currently 'host' several Tek scopes that were cutting edge 50+/- years ago and that I'd literally give away to a good home, and that I have only because I rescued them from a worse fate that they didn't deserve (and they are redundant to other scopes I have and that I'm more inclined to keep)

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    If you want continuous power monitoring, consider a PC with data input cards and some software. I used to do this my last job, use an optoisolator, DATAQ or similar AD convertors and software.

    Do a google search using data acquisition and/or software to get started. National makes vary good stuff, but expensive.

    Tom

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    Quote Originally Posted by TDegenhart View Post
    If you want continuous power monitoring, consider a PC with data input cards and some software. I used to do this my last job, use an optoisolator, DATAQ or similar AD convertors and software.

    Do a google search using data acquisition and/or software to get started. National makes vary good stuff, but expensive.

    Tom
    Some time back someone on here had referenced some relatively new and affordable, but pretty capable, power monitor that may have even used something like a smartphone or a bluetooth connection to a computer. I remember being intrigued and impressed with what it was capable of in relation to what it cost. But at the moment I cannot remember details.

    This looks intriguing but I can't seem to see what it costs or how to specifically purchase the hardware
    OpenZmeter | oZm

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    I'm starting to lean toward an AEMC 407, its a clamp meter with some THD capacility, and with the software it appears it may display to higher harmonics than 25th. good thing is its rated for this type of utility work, and not too much $$$, about as much as decent entry level oscilloscopes, but all those I looked at so far don't appear to give a THD%, though they have FFT function.


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