| 摘要 |
An rf oscillator comprising an electric circuit and an optical leg is used to measure physical variables capable of changing the length of the optical leg. In the circuitry, a beam of amplitude modulated radiation returning from the optical leg is converted to an electric signal, amplified, and used to modulate the drive of an LED which emits a beam of optical radiation. The beam is delivered to and returned from a reflective surface at the end of the optical path by waveguide means, phase shifts in the beam due to actual or effective changes in the pathlength of the optical leg are converted to corresponding shifts in the frequency of the oscillator. Details are given of using this in a fluid barometer, differential pressure sensor, fluid velocimeter, Pitot tube, shift position locator and in temperature sensors. Fig. 2 shows the barometer, where the modulated beam from LED 16 is passed to the reflective surface 60 of liquid 54 by fibre optic waveguide 44, the returning beam being separated by beam-splitter 26 and passed to detector 22 which modulates the LED via amplifier 20; the resonant frequency varies with the length of path 58 and hence with atmospheric pressure. <IMAGE> |
