potentiometer analyses

[Endy]

I have been trying to run a Parameter Sweep of a set up i have made but i can't seem to get the results I want. I tried to make it really simple, as to eliminate any errors and then make it harder as i went. Any way the results are still off. And i think i know why, I just want to make sure i got it. When i run the is is the total resistance i change right? So there is really no point in running a parameter sweep on a potentiometer, as when i change the value in the sweep it is the total resistance i change, and 20 % of x Ohm will always give the same voltage. Instead if i wanted to get my answers for a 20% potentiometer, lets say i use a 10 k Ohm potentiometer, I have to serial connect 2 resistors on at 10 k Ohm and the other at 8 k Ohm and then measure the voltage in between them to get the same answer, with its 30/70 k Ohm and so forth. My question, if all above is correct, is there a smarter way to do it in Multisim, or should i just use a math program to get the answers I want?

Regards

P.S English isn't my native language, I hope I made my self clear in my question. If not I will try and clarify it.

[yyao]

Hi Endy,

You can't perform a parameter sweep on a potentiometer the way you expect to. This is because a potentiometer is implemented as 2 resistors in series in Multisim. When performing a parameter sweep, you can only control one variable at a time. Thus, only one of the two resistor values change, which is probably not what you want.

You could be a little creative and try modeling a potentiometer with 2 VOLTAGE_CONTROLLED_RESISTOR_VIRTUAL's. This device changes its resistance based on an input voltage. You can set up the circuit so that as one control voltage increases, the other one decreases. Then, you can perform a parameter sweep and vary the control voltage.

Hope that helps.

[foobar617]

Can you provide a screenshot of the setup you have for the VOLTAGE_CONTROLLED_RESISTOR_VIRTUAL devices? I'm a newbie and I can't quite figure it out.

Thanks.

[yyao]

Hi there,

Take a look at the attached schematic. By varying V1, you are varying the resistance of U1 and U2 simultaneously, thus simulating a potentiometer. V1 should be swept between 0 and 5V for full range of the 5k potentiometer.

Hope that helps.

[tallfellow]

The example given to simulate a potentiometer is referenced to ground . Does it have to be as I want this in the feed back loop of a op-amp .