Will cutting off an AC current affect its measurement?

Discussion in 'General Electronics Chat' started by pokenan, Dec 3, 2015.

  1. pokenan

    Thread Starter New Member

    Nov 19, 2015
    3
    0
    Hi all

    Let's say we have a 200A(p-p) sinusoidal AC current. After reaching the peak for the first time, it is cut off at 80A. As the wave hasn't reach its half period, so I am now wondering whether cutting off can affect some properties of AC current. That is to say, firstly, does it still have an RMS value at 200/root2 as a normal consistent AC current? Can the 200A be measured by a current meter? Will it be considered as a changing DC current since it has always been positive? Will the magnetic field be totally different from that excited by a normal consistent AC current?

    Thank you for your attention and help.

    Kind regards
    pokenan
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    what happens to the light when you turn it off? same thing, a few switching transients, then nothing left to measure. how can anyone measure 200 amps on an open circuit?
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    The RMS value of a waveform is a measure of a steady-state condition. Turn-on and turn-off transient conditions and discontinuities are fundamentally different from steady-state conditions. That is why an early course in EE is called transient analysis. Yes, you can calculate the RMS value of a partial half-cycle of a sinewave, but it is not simply Vpeak/root2.

    And yes, an interrupted AC or DC magnetic field is totally different from a steady state field. That's where the flyback kick comes from.

    ak
     
    pokenan likes this.
  4. pokenan

    Thread Starter New Member

    Nov 19, 2015
    3
    0
    Thank you for reply. Another question, for transient DC current which rises from 0 to 200A then drops back to 80A, when analyzing, does it make sense if I consider the rising and dropping part as a part of an interrupted AC?
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    Not to me. In my mind, AC or DC - anything AC or DC - is a steady state condition. Rising and falling DC isn't very D, is it?

    ak
     
Loading...