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oscilloscope flickering

Hi all!

I am new to Multisim and this one thing has been very annoying - how to stop my oscilloscope screen from flickering when it collects data?
I tried changing the trigger and when it's on "Norm" it keeps drawing the same signal again and again (at some 3-4 times/sec). When it's on "Sing" it draws the signal only once but the background keeps flickering over and over.
A regular, "physical" scope has no flickering screen (or at least not a visible one) Smiley Happy  

What can I do?

Thank you all !!

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Message 1 of 7

I don't think there is anything that you can do to prevent this. You have to realize that the simulation is not in real time and is naturally slower. This is why the scope flickers. You could try to speed up the simulation by ajusting the TMAX under the Default Instrument Settings in the Simulate Tab. This will help but won't cure it. Try setting it to 1E-03. The only drawback is the introduction of minor errors in the simulations calculation process. This isn't significant but can produce singnals that just don't look like they should (i.e Square waves that are not totally square, Sine waves that are more triangular in shape, etc).

One other option is to use the Transient Analysis function under The Analysis Menu. This by-passes the scope but produces the same results that are viewable through the Grapher. The only thing is that you have to set the time and ouput variables manually with the dialog boxes within the Anaylsis Window. The result is diplayed on the Grapher just like a trace on the scope.

I hope I answered your question and ddn't confuse you. If there is another way. other than what I have suggested, I would like to know too.

Kittmaster's Component Database

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Message 2 of 7
Could TMAX setting also be the reason why it takes 3min for the scope to "collect" one period from 1Hz sine signal??
Or is there a better way to "speed it up" ??

Thanks a bunch!
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Message 3 of 7

I am not sure exactly how you mean "3 min". It took mine only 1 second of "simulator time" which represents what the real circuit timing would be. In "real world time" it took the simulator 25 secs to actually simulate this using all default settings. I am not sure why it would take yours 3 minutes to do this. You could try adjusting TMAX to a lower value to increase the speed, but it seems that there may be something else that is causing your problem with this 1 hz signal.. 

My set up for this was to use the AC_VOLTAGE_SOURCE alone connected to the O-scope. If your using anything else like the 555 timer or another component to generate your signal then this would lengthen the "real world" time it takes to simulate this significantly and TMAX adjustment would definely improve the situation.

That's about all I have. If soemone else has any suggestions please post them. 

P.S.. If your wanting just to generate a signal, use the function generator. I just tested it and it is extremely fast (almost real time). It flies compared to the AC_Voltage_Source that I used in my test. This is something I didn't know so I learned something here too.

Kittmaster's Component Database

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Message 4 of 7
It's something like this: 0.1sec "simulator time" = 15sec "real-world time" (i.e. my waiting to see the results). Everything is on default and i have the function generator directly connected to the simplest scope (function generator makes 1Hz signal)  
How to change this? And, sorry for asking again, what does TMAX really stand for?

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Message 5 of 7
TMAX  stands for Maximum Timesteps (I know this is backwards it should be called Timesteps Maximum). Basically this is the time resolution of the simulator. The lower this number is the slower the simulation runs but the higher the accuracy of the results. The higher this number the faster the simulator runs and the lower the accuracy of the results. So, the default is set to 1E-05. If you change this to 1E-03 you are actually increasing this number and lowering the resolution of the simulator.
This sounds strange but if you think 1E-05=.00001 and 1E-03 =.001 then you can visualize how this works. It took me a while to understand this relationship because it seems backwards in scientific notation.
I am not real sure as to the relationship between these numbers and real time. But I assume that the closer this number is to 0 the closer to real time you would be. I am not sure you could actually get to zero because the simulator needs a certain amount of time to do calculations to converge to a solution for the circuit. This would result in the simulator returning "timestep too small" errors. Most of the time I don't go below 1E-03 to avoid these errors. It doesn't hurt to play with this, if your results don't match what you expect or the simulator starts returning error messages, then you can always go back to the default of 1E-05.
I hope I explained this so you can understand it. I am not the best at explaining things like this. I know it in my head but putting it down it down in print is a a challenge.
Kittmaster's Component Database

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Message 6 of 7

On my previous post I just want add a disclaimer. The explaination I gave is the way I understand it. If it isn't correct or I have misunderstood the way things work please let me know. Multisim is a program that is tough to master and something that you will always be a student of. I think I learn something new about it every day and I have had mine for over 5 years (Multisim 2001 Power Pro).

Anyway, I thought I would just put that in there so everyone would know that even though I am experienced with Multisim , I am nowhere near an expert.

Kittmaster's Component Database

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Message 7 of 7