The coil's resistance to changes in current flow. It directly determines how fast the magnetic field can rise when power is applied. Higher inductance means slower field buildup but potentially stronger peak field. Measured in Henries (H) or millihenries (mH). Inductance increases with more turns and with ferrite or iron core materials. Combined with resistance, it sets the L/R time constant.
Coil current does not switch on instantly; it builds up along this curve, set by the coil's L/R time constant. It reaches about 63% of full after one time constant, 95% after three, and 99% after five. If the pulse is at least about three time constants long, the current has essentially finished building, so the pulse is complete.
