Dear all Hello and Happy New Year,

I run a simulation at Multisim and Circuit Lab of a simple circuit with 3 equal capacitors and a DC voltage source. Why Multisim shows at probe(2) 0V, instead of 8V, and at probe(3) 0V, instead of 4V ?

Circuit Lab gives the expected results. Node(9) 8V, Node(10) 4V

The problem is that voltages at this circuit at the real workbench, can not be measured unless you have an electrometer

Attached the circuit lab and multisim simulations

Thanks for your help

 

What simulation mode and initial conditions are you using for the Multisim simulation?
What are the capacitor sizes different?

You can momentarily measure the voltages in a real circuit using a standard multimeter with larger capacitors (≥10μf).

 

Dear all Hello and Happy New Year,

I run a simulation at Multisim and Circuit Lab of a simple circuit with 3 equal capacitors and a DC voltage source. Why Multisim shows at probe(2) 0V, instead of 8V, and at probe(3) 0V, instead of 4V ?

Circuit Lab gives the expected results. Node(9) 8V, Node(10) 4V

The problem is that voltages at this circuit at the real workbench, can not be measured unless you have an electrometer

Attached the circuit lab and multisim simulations

Thanks for your help

If you look at the Multisim results, you'll see that there is a small leakage current in C1 but not in the other two. It's a bit troubling that they don't all show the same current, but simulators are, in general, non-charge conserving.

Most simulators do not like circuits that have nodes that don't have DC paths to ground because it makes it hard for them to come up with deterministic initial conditions. This is why you often have to add initial conditions to such nodes to even get the operating point calculation to converge for the simulation to start. If it's able to converge without initial conditions being specified, then the resulting values on DC-isolated nodes can be almost anything and this can really mess up further simulation results or, at the very least, require extremely long simulation times for them to work themselves out.

 

Thank you very much both of you.

Multisim needs care to perform simulations. I changed the initial condititions and works as it should be

wish the best for 2019

 

Thank you very much both of you.

Multisim needs care to perform simulations. I changed the initial condititions and works as it should be

wish the best for 2019

One thing to avoid is to draw the conclusion that this means that Circuit Lab is "better" than Multisim. It is likely the other way around -- Circuit Lab effectively has hard-coded things that resolve issues like this in a way that matches what most students expect to have happen. But this usually comes at the cost of not being able to handle the more general cases reasonably because it is too simple-minded.

 

I have thought so, that multisim is more demanding in, let ‘say in programming, thus professional, compared to Circuit Lab.

@crutschow, also I have managed to make a measurement with a simple circuit, voltage follower, with a high input impedance & very low input bias current OP AMP. In real circuit.

thanks again