| 摘要 |
PURPOSE: To enable a laser Doppler speed measuring instrument to detect the extremely small speed variation of an object to be measured by constituting the instrument so that the instrument can decide the wavelength or crossing angle of a laser beam in accordance with the average speed of the object and a required noise level. CONSTITUTION: The output of a light receiving sensor 5 is converted into the speed of an object 7 to be measured as a signal containing Doppler frequency through prescribed signal processing by means of an amplifier 9, BPF 10, counter 10a, and analyzer 10b. The Doppler frequency fD is expressed by fD=2v×sin(θ/2)/λ, where (v),λ, andθrespectively represent the moving speed of the object 7, wavelength of a laser beam, and crossing angle of the laser beam. What is understood from the analyzed results of noise components and the formula is that it is necessary to set at least theλorθto lower the noise level. When the wavelengthλand crossing angleθof the laser beam to be set are found by substituting the lower limit value of the Doppler frequency and average speed of the object 7 into the formula and measurement is performed in accordance with the set value of at least theλorθ, the moving speed of the object 7 can be measured with high accuracy at a required noise level. |
