| 摘要 |
PURPOSE:To provide an endurance against contamination, by utilizing a sharp change in acoustic impedance as caused at one end of a sound tube as the edge of an object to be measured under the tube end with the traversal movement thereof when the end of the sound tube is placed facing the object. CONSTITUTION:The frequency of an oscillator 6 is fixed at omega=omega2n+1 (wherein omega is angular frequency and n=0, 1, 2...) and the object 3 being measured moved to the right. First, the sound pressure in the sound tube 1 is large in the amplitude with the sound tube 1 resonating having one end thereof open but it reduces sharply with the tube 1 shifting to the state of both ends closed as the edge 3 thereof 3 is passing under a flange 2. In other words, the relation between the coordinate value x of the edge 4 and the output E is as shown the solid line in the drawing B and hence, the position of the edge 4 can be detected by the size of the output E. Then, the frequency of the oscillator 6 is fixed at omega=omega2n. If so, since this is resonance frequency with both ends the tube closed, the sound pressure in the tube will increase as te end of the tube is closed with the passage of the edge 4 through the flange 2. As a result, the characteristic becomes as shown by the dotted line in the drawing B and also in this case, the position of the edge 4 can be detected from the size of the output E. |
