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Displaying ripple voltage with a scope?

Discussion in 'Electronic Design' started by Brian, Dec 31, 2003.

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  1. Brian

    Brian Guest

    Look again at the wall transformer---- I believe it will say 60 Hz (not 60 Mhz).
  2. Sam Kaan

    Sam Kaan Guest

    What is the best way to see the ripple voltage with an oscilloscope?
    I want to measure the 16V AC that comes off the wall transformer.
    The back of the wall transformer says Input: 120V 60Mhz 16Watt and
    output is 16V AC 375mA.

    At this output voltage that is being measure 16V AC, is it potentially possible
    to fry the scope?
  3. John Fields

    John Fields Guest

  4. Sam Kaan

    Sam Kaan Guest

    U are right, 60Hz (typo.)
  5. Sam Kaan

    Sam Kaan Guest

    Well I have a used Tek 7904 with mainframe up to 500Mhz. But the plugging
    I have is 7A13 which I think is good up to 100Mhz.

    This is just an exercise only as I have no function generator (getting one
    soon) and itching to see what
    this thing can do.

    just out of curiousity, is it safe (to the scope) to measure the 16V AC
    directly What is the proper
    way to do this? A probe will have the needle and the little alligator clip
    for ground. I can understand
    it in a DC circuit, but where do you ground this in a AC voltage source?
    Could someone please
    give a lowdown on how to set up your scope (probe etc) in order to measure a
    16V AC output from
    a wall transformer. I just want to see that sine wave going across the
    screen for now. Thanks.
  6. Sam Kaan

    Sam Kaan Guest

    Well I am a hobbyist and very new to this. I decided to own a scope hoping
    it will help me learn these stuffs better. I know some stuffs about
    electronics but
    don't have much experience witha scope. Sorry!
  7. Sam, you've been asking a lot of questions lately about this scope... you
    really, really should get the manuals for it. The old Tek manuals are very
    good about explaining everything from the basic principles of operation of
    an oscilloscope, all the way to what the particular scope's specifications
    are and even how to calibrate and maintain it.

    Trying to learn how to use a scope by asking questions on Usenet is like
    trying to learn to drive a semi by asking questions on Usenet, I'm afraid.
  8. Luhan Monat

    Luhan Monat Guest

    No, scopes are generally good to several hundered volts.

    No offense, but it seems unusual to both own a scope and ask this kind
    of question.
  9. Rick

    Rick Guest

    With the price of analog scopes almost cheaper than a good multimeter, I
    think almost everyone can own a scope.

    Your 16V transformer will most likely be isolated from the 120V mains in
    your house, so you should be able to hook the ground (return) lead from your
    probe to one side of the 16V output and hook the probe tip up to the other
    side (polarity doesn't matter in this case...pick either lead of the OUTPUT
    of the transformer for your ground (return) connection. Note that if you
    were to try and measure the sine wave of the 120V(rms) output from the wall
    outlet directly, you would need to exercise caution not to connect the
    ground lead to either side of the wall plug. You could connect it to the
    round hole in a 3 prong outlet if you want, but the scope is going to have a
    return to ground through its power cord (assuming it is not some battery
    operated thingy). Probably safer to use your little 16V transformer to
    isolate you from the mains in any case. Note that you will see a sine wave
    with a peak to peak voltage of about 46V or even a bit higher (since the
    transformer is unloaded). If you looked directly at the wall voltage you
    would see a sine wave that went from about -170V to +170V.

    If you can buy or build a function generator, you could have some fun
    exploring things like low pass and high pass filters, simple transistor
    amplifiers, etc. with just a handfull of parts from even *gulp* Radio Shack.
    I would recommend getting a good book on basic electronics, then maybe
    getting Win Hill's excellent Art of Electronics. I guess you could start
    with AoE, but you may want something a bit gentler.

    Be safe, have fun, happy new year.

  10. John Fields

    John Fields Guest

    Set your horizontal sweep speed to 2ms/division, your vertical amplifier
    to 10V/division, your trigger to AUTO, and your trigger source to LINE.
    Then, adjust your vertical position control until the trace falls on the
    center horizontal line of the display grid and adjust your horizontal
    position control until the start of the trace moves to the first
    vertical line of the display grid.

    Now, if the secondary of the transformer is isolated from the primary,
    just hook your scope probe across the secondary. If you're using a 1:1
    probe you should see a sine wave displayed with the positive and
    negative peaks about 5cm apart and if you rotate the TRIGGER LEVEL and
    toggle the SLOPE control you'll be able to make the trace start either
    going up or going down at exactly 0 volts.
  11. Rick

    Rick Guest

    Excellent description. I might add that the reason you see the sine wave
    traverse 5 divisions (50 volts) is because the 16VAC value of the
    transformer is probably an RMS voltage (root mean square). The peak value
    of ONE HALF of the sine wave is 16VAC * SQRT(2) = roughly 23V. The sine
    wave amplitude will travel from -23V to +23V and back to -23V in one period
    (which for your 60HZ (not megahertz, lol) will be 1/60 sec = 16.7
  12. Luhan Monat

    Luhan Monat Guest

    Well, then good for you. A scope may be the best thing to buy first to
    learn electronics. It lets you 'see' what is actually going on.
  13. Jim Yanik

    Jim Yanik Guest

    C'mon,John give the guy a break,he's a newbie(or it's a typo).It's a 60
    *Hertz* transformer,and since it ouputs AC(alternating voltage)there is no
    AC ripple to be measured.It's ALL ac "ripple".All he will see is the peak
    to peak(p-p) AC sinewave.(the marked rating is the *RMS* value under some

    And Sam,you will not fry your scope measuring the isolated low voltage
  14. OhBrother

    OhBrother Guest

    Not to take things off in another direction, but I'd like to relate a trick
    shown to me by my "elmer" many moons ago (his ham call was W9CSS by the

    We had just finished building a power supply and he said "Now, let's measure
    the ripple".

    He connected an oil-filled capacitor in series with the DC output and set a
    VOM on the AC range between it and ground. He then switched the meter into
    one of its more sensitive ranges, and read out the small amount of ripple.

    I was 16 at the time and was duly impressed. Hopefully someone can make use
    of this.

  15. IcePhoenix

    IcePhoenix Guest

    60 Mhz Mains?!? That sounds extremely unusual... I would think that would be
    60Hz mains for nearly every standard power transformer, especially if it is
    a "wall" transformer... <G>

    As far as the "ripple voltage" is concerned, that is a component of
    rectified AC, more commonly known as DC...
    Rectified voltage usually has a capacitor inline with it to smooth out the
    "ripples" between the crests of each sine wave. The larger the capacitor
    used, the smoother the "ripple" in the DC voltage. AC voltage is ALL ripple
    as it varies from "negative" to "Positive" voltage 60 times per second.

    If you are hoping to see how "precise" the voltage is, you can either set
    the Volts/Division lower i.e. 2v instead of 5v and adjust the 'centerline'
    up or down to see only the peaks or valleys, or you can set the scope to
    read the "peak" voltage variance... but that requires a fairly "high end"
    (read expensive) scope to accomplish that. <G>

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