Multisim and Ultiboard

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MultisimLive End Time setting


I'm working in MultisimLive with a public Colpitts oscillator circuit. The default simulation settings run for 1e29 seconds. If I leave this as is, the oscillator starts running in about 40ms. If I set the end time to 100ms, the oscillator never starts running and the simulation ends strangely early. What gives? Why would shortening the simulation duration impact accuracy?

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I think I figured this out using my regular seat of Multisim, not the online version:


The "End Time" (TSTOP) setting is used in determining the "Maximum Time Step" (TMAX) variable. For oscillators it's apparently important to set TMAX to something like 1% of your expected waveform frequency, otherwise you may get invalid results that still converge. Since the math relating automatic TMAX determination to TSTOP is somewhat hidden and not awesomely explained, I think that setting TSTOP to something short got me into a bad TMAX situation.


This link explains the issue from Multisim's perspective.


Update: This doesn't solve the problem in MultisimLive. Even if I set the TMAX variable very low (1e-9) and the simulation takes forever, the oscillator never starts running. So there's some difference in the math behind the scenes between the "real" Multisim and the online Multsim.

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