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DVM meters with Square waveform mode

Discussion in 'General Electronics Discussion' started by willwatts, Nov 15, 2014.

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  1. willwatts

    willwatts

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    Nov 15, 2014
  2. willwatts

    willwatts

    106
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    Nov 15, 2014
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    User willwatts has started five threads within the past few hours. I am closing all of them temporarily.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    This thread is now open.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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  6. willwatts

    willwatts

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    Steve check it out again, it's not an oscope, its a DVM meter with a function mode with a square waveform output at only 50hz
    It is right next to the Diode checker mode, it has a square waveform symbol
    It only outputs at 50hz at 2 volts peak to peak

    My question is the use of this mode? what can you test at 50hz? what circuits can I test using a 50hz square waveform

    I heard that one of its use is to test line power transformers, but why would you test a transformer at 50hz? plus if you apply 50hz squarewaveform to the primary how do you measure the secondary of the transformer?

    There is other brands of meters like this that output a square waveform at 30hz, but for what kinds of test? to test what at 30hz?

    Sinometer UT30D Pocket-size Digital Multimeter with Square Wave Generator (50Hz)
    http://www.amazon.com/Sinometer-UT30D-Pocket-size-Multimeter-Generator/dp/B005TLXNPO
     
  7. hevans1944

    hevans1944 Hop - AC8NS

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    The link points me to a cheap imported 3 1/2 digit multimeter. Maybe the "unique build in square wave generator" could be used to stimulate a circuit? No information on what the peak-to-peak amplitude or current sourcing capability is, but for sixteen bucks (plus shipping and handling) I bet it ain't much. Probably a left-over from internal clock circuitry.
     
    Last edited: Nov 17, 2014
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Weird, the first time I followed Danny's now broken link it gave me a list of $US2000+ hand held oscilloscopes.

    Now I know what you're talking about, the answer is simple.

    It is a mostly useless feature added to differentiate the multimeter from others. It's pretty much the same as the transistor tester almost nobody will use it, but it seems like a nice feature to have.

    It's also probably cheaper and easier than a frequency or counter option and maybe people will think that's what it is.
     
    hevans1944 and KrisBlueNZ like this.
  9. willwatts

    willwatts

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    No, it's ment for testing or injecting into an input or circuit
    1.) To test transformers, how can you?
    2.) PWM motors , it's ment for PWM circuits but how so?
    3.) Adjustable voltage control circuits?
    4.) Synchronic clock?
    5.) Calibrate flow meter displays?
    6.) Tachometers
    7.) Frequency input devices

    Look at PAGE#31 of the BK meter it explains it B&K Precision Corp.'sModel 2890A
    https://bkpmedia.s3.amazonaws.com/downloads/manuals/en-us/2890A_manual.pdf
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Well there's your answer. Congratulations.

    Are we finished now?
     
  11. willwatts

    willwatts

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    Nov 15, 2014
    I don't get how they use it to measure , test, check for each one
    can you give an example for each one in the list how it is used and tested?
     
  12. willwatts

    willwatts

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    Nov 15, 2014
    1.) To test transformers, how can you?
    2.) PWM motors , it's ment for PWM circuits but how so?
    3.) Adjustable voltage control circuits?
    4.) Synchronic clock?
    5.) Calibrate flow meter displays?
    6.) Tachometers
    7.) Frequency input devices

    How would it be used and i need examples of how to use it to test, check, measure for these circuits
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Pick one of those and think about it. How do you think your very cheap (but clearly as good as a BK Precision) multimeter could be used with it?
     
  14. willwatts

    willwatts

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    Nov 15, 2014
    1.) I put a 50hz square waveform on the primary of the transformer and use an oscilloscope on the secondary?
    why is 50hz a good test frequency for transformers?

    2.) 50hz to test a PWM circuit ? to see if the PWM circuit is outputting a waveform on the oscilloscope?

    3.) not sure what an adjustable voltage control circuit is or does or what is it used for

    4.) Synchronic clock, i have no idea what this is or used for

    5.) Calibrating a flow meter display using a square waveform out?

    6.) Testing a Tachometer using a 50hz square waveform, i have no idea how this is done
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I'll assume this is the one you chose.

    Why do you think 50Hz might be a good frequency?

    Would it be equally good for all transformers?

    What output would you expect to see on the secondary?
     
  16. willwatts

    willwatts

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    Nov 15, 2014
    Why do you think 50Hz might be a good frequency?

    I have no idea why, why do you think it's a good frequency?
    I would think 60hz because it's line frequency ,
    but 50hz might work for testing line power transformers

    The other DVM meters are at 30hz, which I have no idea what to test at 30hz

    The BK meter is the only one that is a variable frequency and duty cycle square waveform output

    Would it be equally good for all transformers?

    No, just for 60hz line power transformers
    not for testing audio transformers or output transformers
    Maybe for step up and down transformers

    What output would you expect to see on the secondary?

    The same waveform on the primary to the secondary, same voltage and line frequency
     
  17. hevans1944

    hevans1944 Hop - AC8NS

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    Just because some instrument has a "feature" doesn't mean that "feature" is useful. If I want a variable frequency, variable duty cycle waveform to test something I also want to (1) be able to select the waveform (2) adjust the frequency and (3) set the duty cycle (or pulse width)... preferably with knobs not buttons. But that's just me. A dedicated function generator, not a multi-meter, is what I would use.

    Transformers don't pass square waves very well, so I fail to see how exciting their primary with a square wave would provide much useful information measured at the secondary. YMMV.
     
  18. willwatts

    willwatts

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    Nov 15, 2014
    Someone told me the 50hz output is for testing cars fuel injectors pwm circuits. I'm not sure why fuel injectors use 50hz as an input to a pwm circuit
     
  19. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Mains / line frequency is 50 Hz in many places outside the U.S. including the UK, Europe and Oceania. In any case 50 Hz is not too far from 60 Hz. So that might be the right answer - that the meter might be slightly useful for testing mains (line) transformers.
    Good answer!
    Different voltage, unless the transformer has a 1:1 turns ratio.
    Same frequency, yes.
    The transformer will change the waveform too. A transformer that's designed to operate at 50/60 Hz is designed to pass a sinewave, not a squarewave. A squarewave has lots of harmonics, which (by definition) are at higher frequencies than the fundamental, and a mains (line) transformer will not reproduce these very well.

    If you have one of these meters, and an oscilloscope, you can do an experiment to see how the transformer modifies the squarewave.
     
    hevans1944 likes this.
  20. willwatts

    willwatts

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    Nov 15, 2014
    Different voltage, unless the transformer has a 1:1 turns ratio.
    Same frequency, yes.
    The transformer will change the waveform too. A transformer that's designed to operate at 50/60 Hz is designed to pass a sinewave, not a squarewave. A squarewave has lots of harmonics, which (by definition) are at higher frequencies than the fundamental, and a mains (line) transformer will not reproduce these very well.


    The square waveform output of the DVM meters is only 2volt p/p so i don't think a line transformer would do anything

    Yes it passes a sine waveform at 120VAC

    But a square wave at 2 volts p/p it might pass because the voltage is so low?

    This goes back to maybe it's ment for a cars fuel injection or timing PWM circuits for cars
     
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