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8624 Views 7 Replies Latest reply: Apr 30, 2014 12:48 PM by dkemppai RSS
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Apr 14, 2014 10:05 AM

Volts per second versus volt seconds

I've heard the term volts per second and also volt seconds.  First, neither of these make sense, what could they mean?  And second, are they the same or are they something different?

  • boborrob Novice 50 posts since
    Apr 4, 2014
    Currently Being Moderated
    Apr 14, 2014 5:49 PM (in response to Riley)
    Volts per second versus volt seconds

    Do you mean the rate of voltage change across a capacitor for volts per second?  dv/dt?  That's about the only place I can think of off the top of my head where that would work.  And all that is describing is how quickly the voltage changes, as that affects how much current is passed through the capacitor (C*dv/dt ringing any bells?)

     

    If that's the context you're looking for for volts per second, then I don't think they mean the same thing.  A Volt-second is a weber or a measurement of magnetic flux.

     

    Another question, are these two related?  I'm not sure.

  • TMW Novice 2 posts since
    Apr 14, 2014
    Currently Being Moderated
    Apr 16, 2014 5:56 PM (in response to Riley)
    Volts per second versus volt seconds

    Volts per second is also called slew rate.  This is used to measure how fast the output of an op-amp can change (dV/dt).  It is usually expressed in Volts/us. 

     

    Volt seconds is a term used to express glitch energy, such as the glitch when a DAC changes values.  It's just the voltage peak (low extreme to high extreme) multiplied by the length of the glitch in time.  Glitch energy is usally spec'ed at the worst cases which would normally be at the major carry points (ie. 01111 to 10000). 

  • SherpaDoug Novice 1 posts since
    Dec 26, 2012
    Currently Being Moderated
    Apr 30, 2014 12:06 PM (in response to Riley)
    Volts per second versus volt seconds

    Volt seconds is also used in sizing inductors.  As is how many volts over how many (micro)seconds can it take before it saturates.

    • dkemppai Novice 1 posts since
      Apr 30, 2014
      Currently Being Moderated
      Apr 30, 2014 12:48 PM (in response to SherpaDoug)
      Volts per second versus volt seconds

      Volts per second is how fast the voltage is changing. It's the same as the derivative dv/dt, and same as slew rate (usually, slew rate is volts / microsecond or similar value). How many volts do you change in how many seconds. 

       

      Volt-Seconds is often used in transformer design. With transformers, even though you are moving power from the primary to the secondary, you need to ensure that your core doesn't saturate. In this case the volts is relativley constant (usually not changing much), as opposed to above. Volt-Seconds, is volts applied times the number of seconds it was applied for (Thus Volt * Seconds or Volt-Seconds). In a transformer, you need to 'reset' the core, or apply a negative "Volt-Seconds" value so that the average of Volt-Seconds is zero.

       

      Very different values, with similar names.

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