Hello, Prof.S.K. Chakarvarti a écrit : > Has some one tried a mechanical Oscillator using a simple pendulum to > produce oscillations as low as faction of a Hertz(Can replace therefore > Wien Bridge Oscillator for low frequency) with the beauty that the traces > can be seen on an Oscilloscope and there is no need of amplification > required? In my high school (lycée Jean Bart, Dunkirk, France), we are using on a regular base a slow oscillator, which is made as follows: A heavy cylinder hangs under a flexible string, to provide low-freqency oscillations. Some additional threads are added to ensure a good electric conductivity from the top of the spring to the bottom of the cylinder, which is fitted with an insulated copper wire to extend it below. So, when you consider the copper wire below, it is surrounded by insulating stuff, excepted in its lower end, which acts as a small oscilating point, with excellent conductivity. This point is used as the cursor of a "liquid potentiometer". The body of the liquid potentiometer is made of copper sulphate dissolved in water (a very small concentration is enough). A graduated cylinder is filled with this solution. Two electrodes made of insulated copper are prepared; each of them is terminated by a non-insulated copper circle, which is bent at right angle relative to the insulated part of the wire. The longest wire is inserted in the cylinder, so that the bare circle defines an equipotential near the lower end of the cylinder. The shortest wire is inserted higher in order to define another equipotential near the surface of the solution. Both electrodes are submitted to a small regulated voltage. You must check that the electolysis current remains low enough (hence the low concentration of CuSO_4). Then the oscillating part is hung to let the bare copper tip which acts as the liquid potentiometer's cursor, to be in equilibrium near the middle equipotential (as far from the highest circle than from the lowest one). As soon as the oscillator is excited, you get an excellent electric signal by connecting your scope's input to the spring. Best regards, Georges.
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