Basic RC - why the difference?

[Bamber]

Greetings All,

It's a little embarrassing to be posting this low-level question but not knowing the answer as driven me to this last resort.  Forgive me!

I've drawn up a parallel rc circuit as attached.  I've done all the calculations as per text (yes,  I'm a beginner) and no matter what,  I come up with a different answer for the current as compared to multisim 12. I'm guessing that given this is such an extensive program, the error is due to my ignorance of settings, parameters, other formulae, and not a mere bug.   I've tried this in TINA and TINA's answer is the same as mine.   So,  why is Multisim different?  What am I missing?  Please help.

I've posted two files,   one ms12 and one jpg of same.

Regards.   

[johnsold]

I have no idea why Multisim (I do not have it) is producing those results.  I did a careful calculation including the nanohm resistance of the ammeters and got the same results you did.

Lynn

[Bamber]

Thanks, Lynn, for that verification.

Regards

[Tayyab_R · Accepted solution]

Hi Bamber,

I ran some tests with your circuit and the reason why the values are a bit off is because of the timestep being used. The time step determines when the readings should be taken. To solve this issue, go to Simulate -> interactive Simulation Settings and change the settings as shown in screen shot. 

Hope this helps.

[Bamber]

Many thanks for this investigation.   I made change you suggested and certainly the result was better. However,  there was still some error compared to the theoretical values.  Bumping the timestep down to 100 nano secs did improve the result even further.   Are there any guidelines for improving simulation accuracy when using higher frequencies?  

Regards

[Tayyab_R]

Hi,

Generally, the easiet thing to do is to reduce the timestep so that it takes more readings. There are also some advanced settings for the simulation in the Interactive Simulation Settings Analysis Options Tab. You can slect Use Custom Settings and try to modify them. This is usually not required for most circuits but sometimes, you need to modify these to make the simulation run.

Again this is circuit specific so there is no way to say change this setting and it will work. You have to look through these and see what you might need to change.

Hope this helps.