Hi Y'all,
I have been trying to find out what i can about this, without much
success, there doesn't seem to be much about the actual speeds,
although i seem to recall that the speed of electricity through a
wire is rather less than the speed of light.
It might vary a bit with different conductors, i think its between
a half to two thirds of the speed of light.
There are instruments which can send a brief pulse down an open
ended wire, and listen fo the return pulse from the open end.
These instruments are now pretty accurate, good enough to decide
where a crew should dig a hole in the road.
Such an instrument would rely on knowing the speed of the electricity
in the wire, and if different conductors have an effect, then this
would be part of the adjustments available to the operator.
I feel sure someone on this board would know more precisely
However, back to the spark.
Sparks are generally weird shapes. They travel from point to point
in a haphazard sort of way, i would guess that this could vary the
distance involved up to about a third more than the direct route
would be.
Also, i think that (breakdown) sparks start from both points, then
sort of meet somewhere in between.
There is another type of spark, a drawn type of spark. These do not
rely on an extra-high voltage to cause a breakdown of ionised air (if
in air), because they occur when conductors disconnect and move apart.
These type of sparks can be quite destructive to the surfaces
involved, and much work goes into making sufaces which withstand
this treatment fairly well. This type of spark is a study of itself
and is not the type of spark which i would be trying to use.
If the spark is considered as a conductor, then the speed would be
relative to the distance involved.
I haven't got as far as that yet, but the distance i will be trying
is likely to be quite small, i would guess at around a half of a
millimetre, but i really don't know how far a couple of hundred volts
can jump, so i will have to fiddle around.
Maybe someone on this board could put some numbers to it ?
So i really can only guess at the speed of the rise time involved.
Other factors affect the rise time too, as has already been said,
but these factors are generally understood and known.
As i have said, i don't think there will be much to choose between
the speed of electronics and a small spark.
But i think i will end up with an electronic arrangement because of
the possibility of interference. Sparks seem to be notoriously
difficult to screen compared to electronics.
And also for controlling the repetition rate. This may turn out to
be important, i dunno yet.
Thank you all for your interest and comments, John