Tham khảo tài liệu 'gear noise and vibration episode 1 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 80 Chapter 6 Fig Simple circuit for fixed gain charge amplifier. Where consistency robustness and reliability matter these basic single purpose circuits can be preferable to the standard commercial boxes which must cater for an extremely wide range of operating conditions and are correspondingly much more complex. A standard die cast box will take the circuit with its mains adaptor or batteries rechargeable and can easily be sealed against showers so that it can operate outside in all weathers. Any high input impedance 100Mfì operational amplifier with a gain-times-frequency response 1 MHz can be used. It seems wasteful but a convenient amplifier to use is an LF444 or LF347 which have 4 op-amps on a single cfrcuit as single versions of this performance are not easily available and it is easier to use one amplifier for a range of requirements. Using a standard 2 very economical accelerometer of mass about 20 gram with a typical output of 27 pc g pico Coulombs of charge per g acceleration we have about 600 mV per g acceleration or 60 mV per m s2. As the frequency drops the acceleration which is proportional to frequency squared drops rapidly so that by 5 Hz an amplitude of 1 pm is only giving g and is well down into the electrical noise level unless special accelerometers are used. The electronics to deal with the small charges at low frequencies below 1 Hz start to become more complex. In addition at low frequencies the equal and opposite quasi-static forces at wheel and pinion bearings tend to cancel so there is negligible vibration to measure. None of this affects audible noise investigations since we cannot hear vibrations below 32Hz off the bottom of the piano unless they are incredibly powerful and they are then felt rather than heard. As mentioned previously users who think they hear 2 or 3 Hz noise are in fact hearing modulation of much higher frequencies. Copyright Marcel Dekker Inc. All rights reserved. Marcel Dekker Inc. 270 Madison Avenue New .
