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L/R Time Constant

Engineering
How quickly current and magnetic field build up in the coil when power is applied. This directly affects how sharp and strong the pulse edge is. A shorter time constant means faster rise and more responsive pulses. Tau = L/R where L is coil inductance (Henries) and R is total series resistance (Ohms). Current reaches 63% of its final value after 1 tau and 99% after 5 tau. The pulse width must exceed 5 tau for the coil to fully build current and deliver maximum peak Gauss.
How coil current builds up over the L over R time constantA rising curve showing coil current building toward its final value. It reaches about 63 percent of final after one time constant, 95 percent after three, and 99 percent after five. A pulse is essentially complete by about three time constants.100%63%1τ (63%)3τ (95%)5τ (99%)pulse essentially completeTime (multiples of the L/R time constant τ)Current built up (% of final)© 2026 Gauss Labs
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.
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