Measuring High Voltages using Spark Gaps

For spark gaps in air, I have heard people say it's 30kV/inch and I have also heard people say it's 30kV/cm. It turns out that both figures can have an element of truth - for needle gaps and 'perfectly linear' gaps respectively. For sphere gaps where the gap is less than the sphere diameter then the electric field remains relatively linear so corona does not form ahead of breakdown and this makes the gap strength much less dependent on pulse shape. For needle gaps there will be electric field stress raised around the needle points causing corona, and this makes the gap strength less predictable for pulse waveforms. You can use sparks between spheres of known size along with the curves included in this video to make a reasonably good estimate of your high voltages, regardless of whether it is DC, AC, or pulsed. I have not mentioned that there are also effects from air pressure and humidity that would affect an accurate measurement, however I don't think we need to worry about that for this purpose of estimation. Of course, it is important that your HV source should be current limited, either internally by design or by a suitable resistor, before connecting it to a spark gap, otherwise you might get a very loud bang! Happy measurements. Thank you for watching - please give a thumbs-up if you liked the video, and please subscribe if you want to see more.