I have a HNC Lab assignment coming up. As part of the prep for the lab work we have been given an RLC series circuit for which we had to calculate some values such as volt drop , Wn, Q and Bs, which I've since done. We then have to use simulation software, in this case Multisim, to simulate the circuit and compare the values measured to the values calculated.

Currently I'm stuck on measuring q factor and bandwidth within Multisim. I'm assuming an oscilloscope should be used but I'm unsure where it should be connected and how to interpret the plot received. I've been searching google for a couple of days but cannot find any information.

The values of the circuit are R 500Ohms, L 56mH, C10nF, Vs 5Vpk @ 10KHz. I used Wn = 1/ Sqrt(LC) to calculate the resonant frequency, which came to 42.258k. I've confirmed this within multisim.

Any help would be much appreciated.

  • \$\begingroup\$ So basically you are asking how to do the work you have been assigned and was supposed to learn? Do you know what is special about resonant frequency in RLC? How can you detect it? \$\endgroup\$ – Eugene Sh. Jan 5 '16 at 15:40
  • \$\begingroup\$ The web of wonderful things is a really useful tool for students of all ages and abilities and should always be your first port of call - electronics-tutorials.ws/accircuits/series-resonance.html \$\endgroup\$ – JIm Dearden Jan 5 '16 at 15:59
  • \$\begingroup\$ Yes, I am asking for help for the work I have been assigned to do, as we where emailed the work after we broke off from college for xmas as the assignment had not been fully written, and it is to be completed for the 1st day we get back. We've not been shown how to do work and our tutor has not been too responsive due to it being the xmas period. Not sure what the problem is, this is a site for asking for assistance with problems is it not? \$\endgroup\$ – ShadyBaby Jan 5 '16 at 16:10
  • \$\begingroup\$ Does this help? electronics.stackexchange.com/a/28323/6383 \$\endgroup\$ – JimmyB Jan 5 '16 at 16:18
  • \$\begingroup\$ I have already calculated all of the values I need, I'm not asking people to do my work for me. Like I said in the original post, I'm asking for information on how to work out Q and Bandwidth using Multisim so I can compare the measured values to my calculated ones. I've the last 2 hours looking for information on the web but can't find anything that's helping, hence my post here whilst I continue to search. Not sure why the first couple of comments needed to be put so sarcasticly \$\endgroup\$ – ShadyBaby Jan 5 '16 at 16:22

Bandwidth is an AC parameter, so you should run an AC sweep to find it. I haven't used Multisim in years, but I seem to recall there being a Simulation menu, and it was in there. From there you can calculate Q using the definition \$Q=\dfrac{f_r}{\Delta f}\$.

  • \$\begingroup\$ This is exactly how to do it. Also note the df is from one -3dB point to the other. \$\endgroup\$ – MadHatter Jan 5 '16 at 16:55
  • \$\begingroup\$ Thank you very much for the info. Up until now we've only had a very limited use for Multisim, only using multimeters and oscilloscopes, so I'm not entirely sure what the sweep is, but I'll take a look, it's definitely a start. @MadHatter Out of curiosity do either of you know if there is any way to measure either of the values with components such as Multimeters or Oscilloscopes (as that's what our guidance notes from our tutor have suggested)? \$\endgroup\$ – ShadyBaby Jan 5 '16 at 17:27
  • \$\begingroup\$ @H.Buckton You could put a function generator in there and vary the frequency manually while looking at a scope. That will take more time than figuring out how to use the AC sweep. Here's a start. ni.com/tutorial/12690/en \$\endgroup\$ – Matt Young Jan 5 '16 at 18:35
  • \$\begingroup\$ @MattYoung I think the function generator might be the route I'd be expected to take... I'm not 100% sure but I think we're going to have to do all the stuff we've done in multisim with a physical oscilloscope in the lab too. Thanks a lot for the info \$\endgroup\$ – ShadyBaby Jan 5 '16 at 18:39

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