Multisim Simple pulse with sw?

[yyao]

Hi F.Anderton,

It is not possible to characterize and support every single electrolytic capacitor out there. If you search for 1uF electrolytic capacitors on Digi-Key, you will find 155 different components with different electrical characteristics. You can imagine how difficult it would be to model all 1uF electrolytic capacitors let alone all possible capacitors and other passive devices. On top of that, imagine how difficult it would be for a student starting their study in electronics to choose between the different capacitors.

You are very much right. You should never completely trust any simulator as a replacement for any physical experiment in any field. SPICE is meant to be a method of rapidly testing circuits under different parameters. It is expected that the accuracy of the performance metrics of a circuit in SPICE and a circuit on a lab bench will differ by 20%, often times more. We are very far away from making simulations a complete substitute for bench top experiments.

My best suggestion for making a non-ideal capacitor is to use a hierarchical block. In the hierarchical block, you can place a capacitor and any parasitic components you wish to model. You can save the hierarchical block and use it in other schematics and projects.

Once again, to reiterate what Jeremy said, please submit your suggestions and tell us what draw backs you are encountering. We are very interested to know what our customers think and will do our best to make our product better.

Thanks.

[F.Anderton@Nottinham.ac.uk]

Solved the issue. The wrong argument was pursued, as it certainly did not behave as the one in the real life situation. The capacitor will discharge through the input resistance of the scope, mine is typically 1Meg. The scope in Multisim I couldn't see where it's stated. Is the internal resistance able to be changed as it is with the voltmeter? When I used this measuring device it responded as expected.

[yyao]

The oscilloscope in Multisim has infinite internal resistance. Unfortunately, you will need to place a 1 megaohm resistor manually.

I apologize for this inconsistency.

Message Edited by yyao on 03-17-2009 12:14 PM

[yyao]

Hi F.Anderton,

I have placed a feature request to add input impedance customization to the oscilloscope. Hopefully, it will be incorporated into a future release of Multisim soon.

Thanks for the insight.

[Euler's_Identity]

Wow!  But I'm not so sure which is better.  I think I'd prefer the ideal such that I can tweak it to produce flaw -- I don't want Multisim intentionally breaking the parts on me.  (Yeesh!)  For example, I'd like to see (you didn't post your circuit) that I could measure the voltage using Multisim's meter, to read the voltage stored in the capacitor, but I'd like to see that voltage gradually drop based on the internal resistance of the meter discharging the cap, which can then be tweaked.  Does this make sense?

Let me give another example.  Years ago I was miffed that Multisim hosed up my op amp circuit by showing me unrealistic output.  Huffing and puffing I contacted EWB (Electronics Workbench) at the time.  They calmly told me to check the model I was using.  You see they, to make things easier for learning, incorporated an ideal op amp model and, unbeknownst to me, I was using it and expecting realistic results.  The solution was I learned there was a five terminal op amp model, and now I use them always.  The problem was solved and I learned from it.

I guess what I'm saying is, and I don't work for Multisim (they've likely wanted to shoot me several times [chuckle] over the years), don't throw out the baby for the bath water.  I personally have been using (and, yeah, on occasion cursing) EWB and Multisim for years.  It really is a top notch program when it comes to learning coupled with ease of use.  In fact, just the other day I was offered the "resources" of, I think it was, Altair, like it was the prize jewel.  Frankly, the only resources I'm really interested in is their models.  Multisim is lacking in the model department I've found, but, as I see it, given enough information, most anything can be simulated to some extent.  (After Multisim's burps, I even pulled off a synthesizer the other day!)  Frankly, were I in your class and I was just learning electronics, I believe I'd much prefer the ease of Multisim.  It's just a richer paradigm to work in.

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[Euler's_Identity]

"You are very much right. You should never completely trust any simulator as a replacement for any physical experiment in any field. SPICE is meant to be a method of rapidly testing circuits under different parameters. It is expected that the accuracy of the performance metrics of a circuit in SPICE and a circuit on a lab bench will differ by 20%, often times more. We are very far away from making simulations a complete substitute for bench top experiments."

However, I will say that on not just one occasion Multisim has made me forget! 🙂

The trick I'm finding is knowing when you can go with a simulator part and when the part needs flaws introduced.  I still blame Multisim right off the bat most of the time, but I'm learning not to do it so much now as compared to way back when.  For example, I had Multisim claim I could replace the power company with a circuit once.  Now when I see such things I try to step back and say, hmmm, how did the simulator get fooled?  It's a kinda love-hate relationship.