| 摘要 |
When calibrating mechanical resonators, consisting of a ferromagnetic material, for electromechanical filters by means of a sand blasting or laser erosion device, the resonators are excited into mechanical oscillations via the alternating field of a coil and the frequency of the oscillations of the resonators is measured with the aid of a microphone. To obtain an interference-free microphone output voltage which is as high as possible, the microphone (4) must be arranged in the area of the first anti-node of the air column located between resonator (1) and microphone, and thus closely adjacently to the resonator. To reduce the great wear of the microphone (4) and of the excitation coil (3), which therefore occurs during the calibration process due to reflected sand grains or ejected particles of material, a closed protective housing (9) is provided which exhibits a removable protective plate (5) consisting of insulating material and facing the holder for the resonator (1). Inside the protective housing (9), a sleeve (7) enclosing the microphone (4) and protruding with one end through a hole in the protective plate (5) and displaceable for moving this end close to the resonator (1) is arranged. Two ferrite core pieces (6) are guided through the protective plate (5). The excitation coil can be displaced inside the protective housing (9) so that its core (11) comes to rest against the two core pieces (6). <IMAGE> |
