I have to build the below series RLC circuit , and output its bode diagram using NI ELVIS Instrument Launcher. It is for a bandpass filter, so the output is taken across the resistor. Before proceeding I simulated the circuit on Multisim, and it worked perfectly, however the implementation didn't give me quite the expected results. I measured the two cut-off frequencies, and they had high percentage errors. Any reason as to why this could happen? Does the software assume certain things?
In theory, theory and practice are the same. In practice they're not.
A simulator will happily crunch away on unrealistic values that make real components far from ideal. Some non-ideal characteristics may be simulated for, if you specified them and entered their values, but the real world will always be more complicated.
In your case, your impedances are very low. Consider the current required to drive a 3.3 Ω load. It's just numbers in a simulator that assumes V1 is a ideal voltage source, but V1 certainly isn't. If V1 is a function generator, then it may have output impedance of 50 Ω. That's still a lot higher than the 3.3 Ω load that will be presented to it at the center frequency.
Simulators can be useful, but there is no substitute for actually thinking about the circuit. Use a calculator or let the simulator determine the details of the numbers, but you have to think about the broad picture first. In this case, 3.3 Ω loading on the voltage source should have been a obvious consideration.
Make the input impedance of your filter several times the output impedance of the signal source. If the signal source has 50 Ω output impedance, then R1 should be 500 Ω minimum. Using common values, so 1 kΩ it is. Now the ESR of the cap and the DC resistance of the inductor will be effectively irrelevant, which they weren't when acting against a 3.3 Ω load. At 1 kΩ output impedance, it will also be easier to find realizable values for the inductor and capacitor.
32px - I think the problem with your circuit is the following: At resonance frequency the total load resistance will be approximately 3.5 ohms (neglecting copper wire resistance). This will require a current of app. 0.3 A. I think, this load will overload your signal generator. So - why not using a parallel RLC bandpass?
If you are required to use a series RLC circuit, use a larger ohmic resistor in aacordance with the required quality factor Q=midfrequency/bandwidth=(1/R)*SQRT(L/C).
Example: R=25 ohms, C=15.4µF, L=105mH.