Hi Richard,
I'll try to answer your questions using a bit of phisics...(hope I remember all the stuff <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="

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all the differences of electric potential are ever misured in Volt (dimensionally...in phisic terms : l^2*m*t^-3*i^-1).
So if you think about a 'voltage' (dop) u'll use the volt (derivate) unit to describe its value.
But if you mean the power u'll use the watt (l^2*m*t^-3) or the BTU (british thermal unit) equivalent and their multiples (or also the old HP- horse power, that is 750 watt or so <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT="

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Another issues are the magnetic field force and the magnetic induction and the magnetic moment:
- the first is the oersted (Oe) , generally referred as H,scalar, dimensionally as i*l^-1 or in the SI measured as A/m
- the second is the vectorial induction (B) , dim. as m*t^2*i^-1 , in the SI measured in Tesla and Gauss
- the 3rd is the mag. moment , dim. i*l^2, vectorial, measured in A*m^2
From a PI point of view what's really matter are the last three params and the voltage spike is just a result of the mutual induction between the coil and the target mag. paths.
This can change A LOT from machine to machine, depending on the tx switch and supply and even more from the coil shape, size, ect.
For more informations take a look at the Corbyn's article (part one) on the geotechnology page.
For the time/pulse width ...generally speaking... if you use higher frequencies (fpr) e.g. some KHz u'll find (generally) a faster response on smaller targets...but it's just becouse of the integrator circuitry that is used in almost all PI design. (see the Eric post about for more details).
The pulse rate is critical becouse (see Corbyn's article again) u'll focus on small and well defined 'time constants' for the smaller targets and if your pi doesn't allow a right (small) delay, flyback drop it'll never see any small obj.
Hope this can help you,
Massimo