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Measure High Voltage using Coil Inductor

  1. Jul 25, 2008 #1
    Hi everybody,
    I need to indirectly measure the high voltage across a wire, which is one of the leads to a spark gap. I ran the wire through a coil inductor(air core) and measured the voltage across the coil leads with an oscilloscope when i get the spark. I also connected a resistor in series with the coil wires and measured the voltage across the resistor with the oscilloscope to get the current (all as a function of time). Can I calculate the voltage and current across the high voltage wire using the dimensions and electrical properties of the components?(inductance,etc). thanks
  2. jcsd
  3. Jul 25, 2008 #2
    Not sure if this helps but you will have a primary coil and a secondary coil the ratio of the voltages is the same as the ratio of turn in each coil. V1/V2 = N1/N2. So if you know the number of turns in each coil you can calculate the voltage. I am pretty sure that the current will be in the same ratio but inverse i.e. V1/V2 = I2/I1.
  4. Jul 25, 2008 #3
    I don't wanna do it through a transformer setup. I'm afraid the current might be too high in the secondary coil.Besides i need to find the efficiency and stuff.Just trying to keep it simple.
  5. Jul 25, 2008 #4


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    Staff: Mentor

    What is the bandwidth of the HV signal? If it is fairly low frequency or DC, you can use a low-frequency HV probe with your oscilloscope:


    You can even make one yourself (be careful!):

  6. Jul 25, 2008 #5
    I thought about that, yeah its just a single pulse dc.But its a very short pulse, like 100 microseconds or something.Its more like a sawtooth signal so maybe i should consider it ac.The problem is I live on a small island..seriously..so i can't get a probe.Maybe i should make one, tho i'm trying to make this whole thing simple and basic as possible.
  7. Jul 25, 2008 #6

    Are you trying to measure at what voltage the spark gap breaks down for different dielectrics or something of that sort? If not, then you can probably just measure the distance between the spark gap electrodes and using the dielectric constant for air, just arrive at the voltage applied. This should give you a rough figure of the voltage. (Note: since you live on an island, do not use the dielectric constant for dry air.)
  8. Jul 25, 2008 #7


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    Staff: Mentor

    I think you meant the breakdown voltage, as described by the Paschen curve. Here's a reference to that info for the OP:


  9. Jul 25, 2008 #8
  10. Jul 25, 2008 #9
    thanks guys but this is for a journal paper.i'm sure referees will grill me for estimates based on the spark distances.i need something more direct than that. i didnt wanna derive the equations for the setup i specified but i guess i have to do that. I thought it would be a common example on textbooks and stuff but i couldnt find it online really.
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