Multisim 10 - problem

[whiz115]

Hi

i'm not familiar with multisim i got the demo yesterday so i can test some circuits without actually build them... but before that i had to learn Multisim a bit, so i had to start with simple ones as the photo shows.

But i'm facing difficulties... the multimeter doesn't always measures and also the oscilloscope.

in the photo i'm posting i was able only to use the oscilloscope but the multimeter shows nothing no matter how i'm connecting it.

and i'm also having the impression that sometimes the multimeter gives false readings...

 

[techie]

Oscilloscope doesn't work because you didn't connect the - of A channel. Connect it to your circuits ground.

I used to use Multisim and all i have are bad experiences with it. It's performance is slow when simulating circuits and if there is any active elements it tends to be vary inaccurate and mostly produce false results. I tried simulating the vary basic transistor circuits as well as more complex circuits with integrated circuits and >2 active elements.
I switched to LTSpice VI and it is A LOT better. It is fast and so far accurate.
You can get LTSpice here:
Linear Technology - Design Simulation and Device Models

 

[whiz115]

Oscilloscope doesn't work because you didn't connect the - of A channel. Connect it to your circuits ground.

In the above photo the oscilloscope works fine!! exactly as you see it connected...but the multimeter doesn't.

 

[Mikebits]

What freq is you signal gen? Are you trying to measure AC or DC? Try meter on top side of R3.

 

[whiz115]

What freq is you signal gen? Are you trying to measure AC or DC? Try meter on top side of R3.

it does nothing...either on DC or AC i had to redesign the circuit so i can make the multimeter work, but then the oscilloscope doesn't work!

can i count on this program or not?


Ltspice is known to me long time now...but it's not so friendly as multisim.

 

[microtexan]

Try placing a ground in the circuit. I have found that to be a problem on numerous occasions.

 

[whiz115]

Try placing a ground in the circuit. I have found that to be a problem on numerous occasions.

did nothing...

does it worth spending more time on it or it is only good on drawing circuits?

can somebody draw my circuit and then tell me if everything goes allright?

 

[whiz115]

nobody?

 

[techie]

I tried and everything is working. Oscilloscope is working and multimeter gives all readings. Works fine. As i said in my post before. YOU NEED GROUND !

 

[Roff]

I tried and everything is working. Oscilloscope is working and multimeter gives all readings. Works fine. As i said in my post before. YOU NEED GROUND !

View attachment 24313

Why does the generator not have a ground? Is it implied? What if you want a floating source? Does Multisim have one?

 

[whiz115]

I tried and everything is working. Oscilloscope is working and multimeter gives all readings. Works fine. As i said in my post before. YOU NEED GROUND !

View attachment 24313

as i said it does nothing, check my photo...

if it is my mistake i need to know..cuz if i fix it then this program can help solve many problems i got with some circuits.

 

[Roff]

as i said it does nothing, check my photo...

if it is my mistake i need to know..cuz if i fix it then this program can help solve many problems i got with some circuits.

What do you mean,"it does nothing"? Your scope seems to show an output. That indicates that Multisim is working. It may not be what you expect. That is generally a problem with you circuit, not with the software.
What were you expecting?

 

[whiz115]

What do you mean,"it does nothing"? Your scope seems to show an output. That indicates that Multisim is working. It may not be what you expect. That is generally a problem with you circuit, not with the software.
What were you expecting?

first of all it's not about the scope it's about the multimeter it doesn't show anything either on AC or DC... that's what i'm saying on my posts.


then after i uploaded the last photo i've noticed that the value of the output capacitor is wrong... i wanted it 4.7uF and accidentaly choosed 4.7pF

and i'm asking... is that how the ouput waveform look like if the input is 50Hz and passes through a 4.7pF output capacitor?

 

[Roff]

first of all it's not about the scope it's about the multimeter it doesn't show anything either on AC or DC... that's what i'm saying on my posts.


then after i uploaded the last photo i've noticed that the value of the output capacitor is wrong... i wanted it 4.7uF and accidentaly choosed 4.7pF

and i'm asking... is that how the ouput waveform look like if the input is 50Hz and passes through a 4.7pF output capacitor?

I was wondering about the 4.7pF cap. If the scope has infinite input impedance, then it doesn't matter what value the cap is. Personally, I would get rid of the cap and connect the scope directly to the collector.
I don't know why the multimeter doesn't work.

I think this statement of yours is ironic:

Ltspice is known to me long time now...but it's not so friendly as multisim.

Friendly, huh? Yeah, riiiiiiight.
I use LTspice, and it works. I have seen many complaints about Multisim on various forums.

 

[whiz115]

Personally, I would get rid of the cap and connect the scope directly to the collector.

i don't want any dc offset! ok?

Friendly, huh? Yeah, riiiiiiight.
I use LTspice, and it works. I have seen many complaints about Multisim on various forums.

the case proves you're right on that...

but for some reason i think that i must be doing something wrong and that's why it behaves like that! i can't believe that it can't work correctly with such simple circuits.

 

[Roff]

i don't want any dc offset! ok?

Put the cap back in after you figure out why you are getting pulses on the output (I'm assuming you were expecting a sine wave).
PS I know why. Do you?

 

[techie]

That generator your using i never used anywhere.
So i tried with it and with an AC source. Results were the same.




Considering multimeter, it takes time for it to start displaying values (5-10 sec).
Also values oscillate from 40mV - 350mV (it doesn't oscillate for ac source).

 

[audioguru]

The generator voltage of 1V is way too high.
The transistor has a voltage gain more than 100 so it is badly clipping.

 

[whiz115]

Put the cap back in after you figure out why you are getting pulses on the output (I'm assuming you were expecting a sine wave).
PS I know why. Do you?

i'm getting pulses no matter what i do with the capacitors! the difference without capacitor is that dc offset exists.

i guess the signal is clipping... but that's minor... while i don't know wht's wrong! maybe i should change vesion of multisim?! to be exact it's not 10 it's 10.1.............................................

 

[Roff]

i'm getting pulses no matter what i do with the capacitors! the difference without capacitor is that dc offset exists.

i guess the signal is clipping... but that's minor... while i don't know wht's wrong! maybe i should change vesion of multisim?! to be exact it's not 10 it's 10.1.............................................

You get pulses because the gain is too high for your signal amplitude, as Audioguru said. Make the input voltage lower, or put a resistor between the signal generator and the input capacitor.