Connect with us

Cheapest tool to measure Total Harmonic Distortion

Discussion in 'General Electronics Discussion' started by Peter2016, Mar 19, 2016.

  1. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Working on it. What I found out so far is that the desktop PC mic need to be set at zero for it to work. But if I do the same for the Asus netbook, it goes crazy in the values. But I found out that setting it at 1 makes it work. Except the value for THD is 5.6 instead of 4.9 on the Pc. Still working on it.

    P.S. I haven't yet found the Line in volume like you showed in your earlier post.

    UPDATE: Got it! It looks like it took a minute for the netbook to settle down and I now have the same value for THD on both desktop and netbook. Now I just have to drag the two generators out from the basement and take measurements :(
     
    Last edited: Mar 21, 2016
  2. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    In the meantime, here is my electricity at home.

    Home electricity1.jpg Home electricity2.jpg
     
  3. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    No problem, take your time.
    Using the mic input isn't "optimal" because this input is actually putting out a small DC voltage to operate the mic (it isn't a dynamic mic like is usual stereo gear, it is an Electret one).

    If you still wont to use the mic-in,
    a small modification to the diagram above is needed:
    Disconnect the wire from the "ring" (middle contact )
    and leave only the "tip" and "sleeve" connected.
     
    Last edited by a moderator: Mar 22, 2016
  4. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Well, everything has been welded... and then used electrical tape. I didn't use a box. I simply cut the electrical cord and inserted the resistors.

    Are you saying the 4.9% THD is not accurate? I would love using the Line In volume setup like you showed above, but I haven't yet founded it on the PC!

    P.S. I'm an idiot and don't have a clue what the last two lines you wrote means. And my first tongue isn't English. I would need another diagram. :( But I will try to find that Line in as I would prefer to not modify my creation.
     
    Last edited: Mar 21, 2016
  5. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    Looks like you are using both the scope channels.
    Try to see which one gives the lower THD result and use only that one(turn the other one off).
    Would be easier to take the netbook to the basement ...;)
     
  6. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Having some difficulty getting only one channel in the Oscilloscope page. Will keep working on it.

    Btw, I now know why I couldn't find the Line In on the Asus netbook. There is none!!! On the Compaq desktop PC, yes there is one at the back of the PC. But not on my portable computers.

    In any case and although I would like very much to have a measurement 100% accurate, it looks like using the mic is still very good. I plugged my creation in the Line In of the desktop PC and got 4.83. While using the mic at the front of the desktop PC produces between 4.94 and 5.01. So the variation is +2.6%. See pic below from the Line In.

    If you want to do me another schematic (for mic), I can built another one...

    UPDATE: I just checked the mic THD after finishing typing this reply and it is hovering around 4.89. So it looks like mic is adding less than 2%.

    UPDATE 2: Yep, after spending even more time observing the mic and Line In I can confirm that the difference between the two is almost negligible.

    Line In.jpg
     
    Last edited: Mar 21, 2016
  7. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Got some results for you. I took the 3000W generator outside (kind of cold right now... and not so easy to see the screen of the netbook outside...) and at idle THD is like household electricity with a THD just under 5%. But when you apply a load, it goes up. I used a hair dryer with a 500W, 1000W and 1600W settings. But switching the hair dryer between 500, 1000 and 1600W drove the program nuts. At one point the program closed itself down. Not the netbook, just the program. And after I restarted the program I was still getting some kind of crazy values. So I brought back everything inside and even after being inside for a while, it was still giving me some crazy values. But now after the netbook had a 'rest', it is working normal again.

    I will give it another try tomorrow if the weather allows. And I better wear ear plugs ;) But I will not go up and down like I did today. I'll try plugging and unplugging the 'tool' I made between each change in watt consumption of the hair dryer.

    GENERATOR AT IDLE (BELOW)

    propane2.jpg

    GENERATOR AT IDLE (BELOW)

    propane 3.png

    HAIR DRYER AT 500W (BELOW)

    hairdryer500.jpg

    HAIR DRYER AT 500W (BELOW)

    haidryer500-2.jpg

    PROGRAM GOING CRAZY AFTER SWITCHING TOO MANY TIMES THE WATTAGE OF THE HAIR DYER (BELOW)

    afterturningoffdryer.jpg
     
    Last edited: Mar 21, 2016
  8. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Ok, so I couldn't wait until tomorrow ;) I screwed up in one Print Screen, so one is missing. So for the hair dryer alone the THD is 12%. I also used the Toshiba laptop instead of the tiny Asus netbook. I'm not sure if connecting the 'device' did something to the netbook, but it doesn't seem to be working with it very well.

    I took a measurement at idle, then with a hair dryer running at 1600W (used a kill-a-watt) and then I unplugged the hair dryer and used a 10amps rated circular saw. And when the saw was running, I added the 1600W hair dryer.

    Since you are, obviously, a thousand times more knowledgeable than me about electronics/electricity; I would have liked to have your opinion on using such generator to only run a chest freezer and a fridge (a regular french door model - no fancy digital display). Do you think the higher THD will make the electric motors run very hot or possibly cause other problems? I would also appreciate your analysis of the quality of electricity. The waveform in particular.

    Thanks.

    Generator at idle (next two pics below)

    gen at idle.jpg gen at idle2.jpg

    Hair dryer running at max heat (1600W) - THD is 12% (screwed up when I did the Print screen so missing one)


    hairdryer1600W.jpg

    12 amps circular saw (next two pics below)

    circularsaw10amps.jpg

    circularsaw10amps-2.jpg

    12 amps circular saw + 1600W hair dryer (next two pics below)

    circularsaw10amps+hairdryer1600w-1.jpg circularsaw10amps+hairdryer1600w-2.jpg
     
    Last edited: Mar 22, 2016
  9. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    Interesting indeed.
    Could you please show only the traces with the scope functioning fine.
    Apart from the THD measurement itself,the spectral content of the signal is also very important.

    Selecting the input channel is done here:
    scope ch select.jpg


    Do you have a spiral heater like this one to use as a load?
    spiral heater.jpg
     
  10. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Hi,

    I just finished 3 hours of testing and I can still hear the generator ringing in my hear... Weather forecast for my area was (supposed to be) pretty bad for today and the coming days, so yesterday evening I brought the gen back in the basement. But today is still ok, so I brought it back outside. Unfortunately, when you wrote your reply I was doing tests, so I only saw it after I was done with my testing. So the results I have will have to do for some time as I am done doing tests for some time.

    Carrying the 107 lbs gen from the basement to the ground floor and then outside is no piece of cake. My back could tell you how it feels...

    In any case, funny you asked about a heater because I had decided to run some tests with one. The one I used is not identical to yours, but you might look into it to see if it is close enough. It is a Honeywell HZ-514 and you can see it here http://www.amazon.com/Honeywell-HZ-514-Electric-Baseboard-Heater/dp/B0072HNOJI.

    My gen is a 3000W/3750W and I can say that I ran it with a 3000W load on the 120V outlet (which only has a 20amps breaker) but it took it without a problem.

    P.S. I did my bachelor in Mathematics & Computers. I would have made a very lousy engineer. That's why I'm pretty lousy at circuits and such. You wrote, "the spectral content of the signal...", this is like Chinese to me. I'll look it up to find out what you mean. Just so you know.

    P.P.S. It is always best to read my reply in the forum instead of the email you get as I can do many editing of my post after my initial reply.

    ELECTRIC BASEBOARD HEATER 970W (NEXT TWO PICS)

    gen2 electric baseboard heater 970W - 2.jpg
    gen2 electric baseboard heater 970W.jpg

    ELECTRIC BASEBOARD HEATER 1410W (NEXT TWO PICS)

    gen2 electric baseboard heater1410W.jpg

    gen2 electric baseboard heater1410W - 2.jpg

    ELECTRIC BASEBOARD HEATER 1410W + HAIR DRYER 1600W (NEXT TWO PICS)

    gen2 electricbase board heater1410W + haird dryer1600W.jpg

    gen2 electric baseboard heater1410W + haird dryer1600W - 2.jpg
     
    Last edited: Mar 22, 2016
  11. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    I read your second sentence a few times, but I'm still at a lost understanding what you mean by, "show only the traces with the scope functioning fine". I duplicated the Print Screen of your first attachment, but I end up with two lines on the scope.

    And I guess by 'spectral content' you mean the waveform on the scope (???).

    So if you wish to try again to explain it to me; I'll give it another try at understanding it.
     
  12. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    Sorry for not being clear.

    1. By "show only the traces with the scope functioning fine",
    I mean remove all cases where as you said in post # 27:
    "the PROGRAM is GOING CRAZY",
    you basically did that already.

    2. Not clear why you can't get a single scope channel working and the other off,but lets leave that for know.

    3.The software show the 'spectral content' of the signal in the frequency window-The same one were it also shows the THD %.
    i.e The "Frequency" window.
    That is the "Fourier Transform" / "Fourier series" of the Signal.

    4."the generator in Idle" at post #28 looks very different than those at post # 30.
    Both the scope signal in time and it's "frequency spectral content" are very different.

    One has harmonics of 60Hz at 120,180 etc.
    The other has a "disturbance" at just under 2000Hz ,4000Hz ,6000Hz etc

    This "generator in idle" is a bit of a puzzle when compared with the heater load cases.

    That high frequency content(2000Hz and above) can be cleaned-up relatively easily ,if it originates from the generator itself.
    But,
    The measurements with the heater produce very high THD% levels ,20% and above,for that I don't think there is a remedy.

    Maybe another set of measurements to clear that up.
    But not yet! we should first agree about what tests to do before .

    P.S.
    What is the generator you are using(Brand and Model) ?
    If possible ,please post a datasheet of it as well.
     
    Last edited: Mar 23, 2016
  13. swagguy8

    swagguy8

    73
    6
    Dec 10, 2014
    the soundcard scope works very well, i have used it myself before. just remember to calibrate it, also remember to use a voltage divider, as it will damage the pc if anything over line voltage ( around 2.5v) is used.
     
  14. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016

    Normally I'm not as sloppy as I've been in the execution of the various tests and usage of the software + dongle (12v +2 resistors). What happened is that testing could only be done with the gen located outside the house and with forecast of rain for days to come, it left me a bit frenetic. If I would have not been dependent on the weather, I would have taken the time to read the manual that came with Soundcard Scope and educate myself a little bit more in matters related to the technicality of electricity.

    2) That is due to a misunderstanding on my part. I looked at your attachment and I thought both waves had to fit perfectly one on top of the other. I can either select only one or do ch1+ch2 which results into a single wave. Which one do you prefer, single or ch1+ch2?

    3) Yes I believe I saw something related to that when I was quickly browsing the manual.

    4) I'm not sure if I misunderstand you here. You talk about gen at idle in post 28 looking different than in post 30. But I didn't post pics of gen at idle in post 30. Maybe you do not need pics at idle from both posts to make such comparison???

    For the sake of clarity and this is something I was going to write about later; I have two identical generators. Bought the same day and both having gone thru nothing more than the 5 hour break-in period. On top of that, I can even tell you that they were both manufactured the same day in that factory in China. Post 28 was done using gen1, while post 30 was done using gen 2. Though I can tell you that when I did the break-in, I used a kill-a-watt and found that gen1 was peaking at 63Hz, while gen2 was peaking at 62.5Hz. As you apply a load, the Hz moves down towards 60.0Hz. With a 1500W load (the gen is a 3000W continuous) the Hz was about 61.5Hz.

    Another preliminary observation is that when the Asus netbook was giving me a THD of 5.0% for home electricity, the Toshiba laptop was giving me 5.5% THD. But this is very preliminary. I noticed that the THD changes depending on the time of the day. During daytime when my neighbors are at work, THD can be found in the 4% to 5%. But when it is around 5pm+, it reaches 5% to 6%. So maybe the higher reading of the Toshiba was only due to the fact it was later in the day.

    As part of my future tests, I will observe the line-in and mic ports of the desktop for 15 minutes each and then use the Toshiba laptop also for 15 minutes in order to compare possible variations.

    The importance of THD is only in relation to possible damages to appliances and other electric/electronic equipment. If THD is 20% but the heater or electric motor can take it then it's fin with me. I intend to use an inverter (not tested yet) for anything like my furnace with an ECM motor and other sensitive things, like TV, PC, battery charger, etc. I just would like to know if a high THD might damage motor/compressor for say, a 10 hour run during a blackout.

    I would be interested to hear about any possible remedy. Maybe I could build one and test it with the gen.

    Definitely, we will need to go over details of the next tests before I execute them. And also make sure you are satisfied with the info I'm getting you out of Soundcard Scope.

    As to the specific generator I was using, please go to http://www.championpowerequipment.com/products/generators/for-home/100215-3000w3750w-generator/. You can also search the web, but I doubt you will find a great deal more info about it.

    What I did yesterday is plugged two chest freezers and a fridge and I ended up with a THD of 7.25. Which is just under the acceptable limit of 8% and can still be considered good. That was the purpose of the propane gen, to be able to run those three things, plus maybe a few small lights and doing it on propane means no hassle with storing gasoline. And it burns so much cleaner than gasoline. Btw, when the 6.5 amps rated motor of the fridge started, the THD jumped to 23 for a second or two before dropping back down to 7.25 (I already had the two chest freezers running when the fridge was added).

    There is a long weekend coming and I don't know my schedule yet, so you might not hear back from me until possibly next Monday.
     
    Last edited: Mar 24, 2016
  15. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
  16. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    The last signal looks like it is a 3 level MSW(Modified Sine Wave / Pseudo Sine Wave) inverter.
    The THD is very high at 26%.
    I wouldn't recommend that for "sensitive" electronic equipment.
    Motors do run hotter and nosier with them.
    Control boards may run faulty and even be damaged by them.
    You can try it at the risk of damaging your equipment.

    What you probably need is what is called a "Pure Sine Wave" inverter.
    They are much more costly than the MSW ones.

    Here is a very basic video comparing them.
     
    Last edited: Mar 30, 2016
  17. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    Hi Dorke,

    Thanks for the advice.

    Ok, so I got tired of waiting for the rain to stop, so I dragged my two gens from the basement into the garage and did additional tests. First I re-did both gens at idle. Hopefully I got the right print screens of data. Let me know if I screwed up again.

    Then I used two ceramic heaters http://www.sunbeam.ca/en_CA/home-co...ic-manual-heater-red/SCH9264R-CN.html#start=9. I also used a 500W halogen light, as well as a 26W CFL light bulb. What is fascinating about this 26W light bulb is that it created as much THD as running the three compressors together (~ 400W - one fridge + 2 chest freezers).

    Your thoughts on the results are greatly appreciated. And if you can come up with a schematic I could execute in order to attempt at modifying the THD I would be more than willing to give it a try.

    Thanks again for your valuable help.

    Generator 1 at idle (two pics below)

    gen1 at idle - 2.jpg


    gen1 at idle.jpg

    Gen 2 at idle (two pics below)

    gen2 at idle - 2.jpg gen2 at idle.jpg
    Gen 2 1450W ceramic heater (two pics below)

    gen 2 -  1450W ceramic heater.jpg gen 2 -  1450W ceramic heater - 2.jpg

    Gen 2 2900W two ceramic heaters (two pics below)

    gen 2 -  2900W ceramic heater.jpg gen 2 -  2900W ceramic heater- 2.jpg

    Gen 1 1450W ceramic heater (two pics below)

    gen 1 1480W ceramic heater.jpg gen 1 1480W ceramic heater - 2.jpg

    Gen 1 2900W two ceramic heaters (two pics below)

    gen 1 2900W ceramic heater.jpg gen 1 2900W ceramic heater - 2.jpg

    Gen 1 500W Halogen light (two pics below)

    gen 1 500W halogen light.jpg gen 1 500W halogen light - 2.jpg

    Gen 1 26W CFL Light bulb (two pics below)

    gen 1 26W light bulb.jpg gen 1 26W light bulb - 2.jpg
     
    Last edited: Mar 30, 2016
  18. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    You did fine.
    Both gen. look the same in no load (idle).
    They have this just under 2KHz(and harmonics at 4Khz,6khz ) spectral noise which disappears with higher loads.
    That is a bit of a puzzle to me.


    The CFL looks like the idle case(it is a very small load),
    but adds just a bit more spectral noise(THD is 7.6% vs Idle of about 5%).


    With "real" load there are the odd orders harmonics (3rd=180Hz ,5th=300Hz,7th etc.)

    It isn't easy to eliminate them.
    One method is to create an "Harmonic Trap" at 180Hz and 300Hz using inductors and capacitors(parallel to the signal path). they would be very bulky.
    I wouldn't recommend that you try it yourself.

    At this point I would contact the natural gas furnace manufacture technical help with the info we have(the pics of the loaded and idle cases).
    Ask their opinion if it would be safe to operate it from the generator or any other issue they think is relevant .
     
    Last edited: Mar 31, 2016
  19. Peter2016

    Peter2016

    23
    0
    Mar 19, 2016
    I find it very fascinating that a 26W CFL light bulb is increasing the THD to the same level than 400W of compressors.

    Thanks for the advice but I don't need to contact the furnace maker. I can already tell you that the furnace won't produce heat when connected to this gen. I tried it for about 15 seconds. Even when the furnace is not producing heat, nor cold (air conditioning), the blower motor is always working at low speed in order to circulate the air in the house.

    When I connected the furnace to the gen with no other load, it ended up consuming 96W (used a kill-a-watt) as the blower motor started to circulate the air, but the THD went straight to 8.6% and the furnace refused to start producing heat.

    Here is a link to a very interesting short read about all this. http://support.fluke.com/find-sales/Download/Asset/3497420_6112_ENG_A_W.PDF

    Thanks for all your help.
     
  20. dorke

    dorke

    2,342
    664
    Jun 20, 2015
    CFL are a known noise source.
    They employ a noisy internal switching inverter .

    You where brave enough to try the furnace with the generator,
    Luckily without damage.;)

    So,
    you don't have a solution for operating the furnace in the case of a blackout(maybe a better and more expansive generator?).
    But sure learned something about the issue :)
    Bets of luck and Take care.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-