Q313 : Modelling a Realistic Square Wave Transient in FFTSES
Question In FFTSES, how can I model a "realistic" square wave transient, i.e. one that has a finite rise time?
Answer The square wave generator model available under the wave-train option in FFTSES is an ideal one, i.e. the rise and fall of the surge occur instantaneously (or more precisely, given the discrete nature of the Fast Fourier Transform, in one time sample).
A more realistic square wave has sides that are sloping, and look somewhat like a "truncated triangular wave".
This kind of waveform cannot be simulated with the wave-train option. You can use the specified surge option to generate such a waveform without too much work. For a square wave of amplitude A, period T and rise-time t, the data should be entered as follows:
Time: 0 Value: 0 Time: t/2 Value: A Time: (T-t)/2 Value: A Time: (T+t)/2 Value: -A Time: T - t/2 Value: -A