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Multisim 10 RC circuit fails

ok, so i'm using the eval to determine what this product can/cannot do before i buy it, and i'm finding many things that are troublesome.
 
1. i made a simple RC circuit. R=500ohm, C=17k uF, 12vdc source. i drop a o-scope probe on the cap thinking i would see the voltage rise to Vcc over a period of 5t. the instant i click simulate the o-scope goes to Vcc.
 
2. then i throw in a momentary switch and a 50ohm resistor to ground from the cap, figure i could now dicscharge the cap and see it on the o-scope. i do see it decay on the o-scope but when i lift off the switch the voltage on the cap stays constant, no rise.
 
i dont get it. either i'm not using Multisim correctly or this program just doesnt work right.
 
anyone?

Message Edited by chuckyRose on 03-23-2007 04:10 AM

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What you see is due to the default settings for your interactive simulation. By default Multisim calculates the initial conditions automatically (not equal to a discharged cap).
To change the settings:
  1. Navigate to Menu Simulate > Interactive Simulation Settings
  2. Select from the drop down list Initial conditions "Set to zero"
  3. Click OK and restart the simulation
 
In addition, you can set specific initial condition for the cap if you want it to be pre-charged to a certain voltage.
  1. Right-click on the cap and select Properties
  2. Activate and set a initial voltage in the Additional SPICE Simulation Parameters section
 
 
Regards
Ingo Foldvari
Area Sales Manager - US West Academic
National Instruments
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Hi,

I was surprised that suppling an initial condition of 100 volts on an electrolytic cap resulted in a negative voltage at the positive terminal with the negative terminal connected to ground.

This seems a bit counter intuitive, and if a smaller voltage was set in a complex circuit, I think I could loose some time trying to find this.

Any opinion?

Regards,

Jim

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Jim,

you are right, I have the same behaviour with electrolytic caps (not with regular caps though) on my installation. I'll report this to our support team.

As there is no report, that lists all initial conditions for parts in a given circuit (I'll file this as a feature request), I came up with this workaround:

Export the circuit as a netlist (menu Transfer > Export Netlist) and search the expoprted text file for "IC=".

 

 

Regards
Ingo Foldvari
Area Sales Manager - US West Academic
National Instruments
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