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APPARATUS

This is a damped driven pendulum with an optical encoder wheel for monitoring angular position vs time.  The driver frequency and amplitude are adjustable.  Damping is controlled with the micrometer that sets the separation between the copper plate and the ring magnet.  The software graphs a phase plot and a Poincare section.

The software includes a simulation for which all parameters are user-controllable.

Sample graphs:

    
       

NOTES

 

Setup: 

The wide ribbon cable sends the drive signal from the driver control box to the pendulum.  The narrow ribbon cable transmits the optical encoder data from the pendulum to the computer interface.  A BNC cable from the "output sync" jacks of the driver to the interface sends a timing pulse at the beginning of each cycle for the Poincare section.  A USB cable connects the interface to a computer.  Currently only the Gateway laptop may be used with this because of a problem installing the device driver on the HP. 

It's also possible to drive the pendulum with an external signal via the "torque calibrate" input jacks on the driver box, with the drive button in the off position so the internal signal is disabled.  The "drive amplitude" output jacks allow you to display the drive signal on a scope.

The resonance frequency is 1.46 ± 0.02 Hz.

Sampling rate is 500 pts/sec.  Maximum number of points is 4x10⁶.

The "save orbit" command saves the next n points (not the currently displayed data) to a text file, with columns: time, angular position (radians), angular velocity (rad/sec), and winding number.  Angular position ranges from -π to +π; so angular displacement can be obtained from angular position + winding number * 2π. 

"Clear" will refresh the phase plot while preserving the poincare plot.

Occasionally the "Halt" command clears the screen.

To recover from the "runtime error:  overflow", disconnect then reconnect the USB cable.