shmoseph
Newbie level 1
Hey
I've built a metal detector using a colpitts oscillator. I used two 1uF capacitors in series. I've been measuring the voltage output from the center tap of the two capacitors. When I bring metal close to the coil, the amplitude of the oscillations goes down to zero.
Can anyone please explain why this happens? Someone told me that it has the same effect as placing a resistor in parallel to the inductor, and in simulation this works very well..but i still don't understand the reason for this effect!
I've attached three pictures to help explain what i mean.The circuit without the parallel resistor shows the circuit and waveform before any metal is brought close to the coil. The other two show the effect on the waveform as metal is brought slowly closer to the coil.Please can someone explain how bringing metal close to the coil gives the same effect as adding a resistor in parallel.. I need to explain it in a project report today!
I've built a metal detector using a colpitts oscillator. I used two 1uF capacitors in series. I've been measuring the voltage output from the center tap of the two capacitors. When I bring metal close to the coil, the amplitude of the oscillations goes down to zero.
Can anyone please explain why this happens? Someone told me that it has the same effect as placing a resistor in parallel to the inductor, and in simulation this works very well..but i still don't understand the reason for this effect!
I've attached three pictures to help explain what i mean.The circuit without the parallel resistor shows the circuit and waveform before any metal is brought close to the coil. The other two show the effect on the waveform as metal is brought slowly closer to the coil.Please can someone explain how bringing metal close to the coil gives the same effect as adding a resistor in parallel.. I need to explain it in a project report today!
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