using oscilloscope on 110AC

Discussion in 'General Electronics Chat' started by absolute0, Aug 3, 2005.

  1. absolute0

    Thread Starter New Member

    Aug 3, 2005
    Can anyone advise on how to monitor 110VAC line using oscilloscope to monitor voltage fluctuations/line noise? Tnx.
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    1. Make darn sure that both the power source for the O-scope and the power that you want to monitor are both wired correctly. Having 110Vrms across your scope's ground lead and case would be a "bad thing." Use an outlet tester to check them.

    2. Hook the probe's ground lead to ground.

    3. Measure the hot lead with the probe.
  3. legac

    Well-Known Member

    May 4, 2005
    Another more safe option is to monitor 110 VAC via an isolation stepped down transformer, i.e 110/6.3 vac.
  4. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    Please don't connect your probe directly to the AC line, you could easily blow your probe or the input stage to your scope. Using a step-down transformer is best, but barring that, attach a 470K (top/hot) and 22K (bottom/neutral) in series and **CAREFULLY** (one handed) measure across the 22K to neutral.

    And, as noted before, your scope should be plugged into the same AC source and properly polarized (hopefully three-pronged AC cord with ground).
  5. pebe

    AAC Fanatic!

    Oct 11, 2004
    Just a word of caution. Neutral may not be at ground potential at your location and if your scope's case is grounded then high currents could flow.

    For that test it would be advisable to temporarily disconnect the scope's case grounding.
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    I must respectfully disagree.

    1) Do not disconnect the case ground of any piece of equipment that is in use. Ever.

    2) Measure from hot to ground - never measure from hot to neutral! If you want to know hot to neutral, then measure BOTH to ground - one at a time - and calculate.

    The earth ground lead is not just a convenient reference point - it is there to protect life and limb.
  7. Erin G.

    Senior Member

    Mar 3, 2005
    I'm not an o-scope expert by any means, but I have to agree with thingmaker3. Grounds are there to reduce shock hazard and should not be removed or disabled.