Figure 7: Chart recorder trace of the photodiode output at three different rotation rates. The mark/space ratio of each wave form indicates the displacement angle as a fraction of 360 degrees, while the period is that of the rotation.
| 4 Experiments and results |
|
4.1.1 Photo-diode Outout
The output from the photo-diode was monitored using a digital storage oscilloscope, and replayed slowly to a chart recorder, for the sarne fluid at three different rotation rates. The resulting graphs are shown in figure 7; note that the apparently slow rise and fall time is in fact due to the chant recorder, not the mechanism itself. The top graph shows the output while the motor is rotating at full speed, and the torque generated is sufficient to fully open the spring to an angular displacement of 180 degrees. The middle trace was taken about half way through me measurement when the rotation rate is such that the displacement is roughly 90 degrees. The lower wave form was obtained near the end of the measurement where the motor speed is low. Here there is only just enough torque to extend the spring, and the angle is very small.
From these graphs it can be seen clearly that the angular displacement of the two disks, indicated by the mark/space ratio of the wave forms, depends on the motor speed. Therefore these results provide some verification of the theory presented in section 2.3 and expectations of section 3.1.
Figure 7: Chart recorder trace of the photodiode output at three different rotation rates. The mark/space ratio of each wave form indicates the displacement angle as a fraction of 360 degrees, while the period is that of the rotation.
| 4 Experiments and results |
|