Driven RLC Circuit (5L20.18)
/Driven_RLC_Circuit_(5L20.18).jpg)
/Driven_RLC_Circuit_(5L20.18)_2.jpg)
A RLC circuit is driven by a 30 VAC, 60 Hz transformer. The amplitude and phase of both the voltage and current for any component in the circuit is shown on an oscilloscope. The capacitance and inductance can be changed to show their effect on the resonance.
1) Slide the iron core of the inductor in or out until the light bulbs are the brightest.
/Bulbs_at_Resonance.jpg)
2) Place the two measurment leads across the source on the circuit board:
/Measurement_Source.jpg)
/Resonance_Scope_Source.bmp)
Note that there is less than half a degree of phase difference between channel 1 (the current in yellow) and channel 2 (the voltage in blue).
/Measurement_Resistor.jpg)
/Resonance_Scope_Resistor.bmp)
Like the source, the voltage and current are in phase.
/Measurement_Inductor.jpg)
/Resonance_Scope_Inductor.bmp)
In the inductor, the voltage leads the current. Also note that the RMS voltage across the inductor is much higher than the 28V (RMS) from the source!
/Measurement_Capacitor.jpg)
/Resonance_Scope_Capacitor.bmp)
In the capacitor, the voltage lags behind the current. Also note that the RMS voltage across the capacitor is much higher than the 28V (RMS) from the source!
Open a couple of the capacitor knife switches to take them out of the circuit. The light bulbs will dim showing that the current is not maximized anymore. Ask the class if the inductance has to increase or decrease to make the circuit resonant. Move the iron inductor core in to increase, or out to decrease the inductance.