机械专业外文文献翻译--对振动侦查和测量的一种实用方法(编辑修改稿)

机械专业外文文献翻译--对振动侦查和测量的一种实用方法(编辑修改稿)内容摘要：

e devices depend on mechanical linkages and electromechanical transducers. Seismic Displacement Transducers. These devices, discussed in detail later, were once popular but now are seldom used. They tend to be large, heavy, and short lived. Double Integration of Acceleration. With the increasing availability and decreasing cost of digital signal processing, more applications are using the more rugged and more versatile accelerometers as sensors, then double integrating the acceleration signal to derive displacements. While older analog integration techniques tended to be noisy and inaccurate, digital processing can provide quite highquality, highaccuracy results. Measuring Vibratory Velocity Transducers. Some of the earliest highfrequency vibration measurements were made with electrodynamic velocity sensors. These are a type of seismic transducer that incorporates a mag supported on a soft spring suspension system to form the seismic (spring mass) system. The magic member is suspended in a housing that contains one or more multiturn coils of wire. When the housing is vibrated at frequencies well above the natural frequency of the spring mass system, the mass (mag) is isolated from the housing vibration. Thus, the mag is essentially stationary and the housing, with the coils, moves past it at the velocity of the structure to which it is attached. Electrical output is generated proportional to the velocity of the coil moving through the magic field. Velocity transducers are used from ~10 Hz up to a few hundred Hz. They tend to be large and heavy, and eventually wear and produce erratic outputs. Laser Vibrometers. Laser vibrometers or laser velocimeters are relatively new instruments capable of providing high sensitivity and accuracy. They use a frequencymodulated (typically around 44 MHz) laser beam reflected from a vibrating surface. The reflected beam is pared with the original beam and the Doppler frequency shift is used to calculate the velocity of the vibrating surface. Alignment and standoff distance are critical. Because of the geometric constraints on location, alignment, and distances, they are limited to laboratory applications. One version of laser vibrometer scans the laser beam across a field of vision, measuring velocity at each point. The posite can then be displayed as a contour map or a colorized display. The vibration map can be superimposed on a video image to provide the maximum amount of information about velocity variations on a large surface. 7 Integration of Acceleration. As with displacement measurements, lowcost digital signal processing makes it practical to use rugged, reliable, versatile accelerometers as sensors and integrate their output to derive a velocity signal. Measuring Vibratory Acceleration Most modern vibration measurements are made by measuring acceleration. If velocity or displacement data are required, the acceleration data can be integrated (velocity) or double integrated (displacement). Some accelerometer signal conditioners have builtin integrators for that purpose. Accelerometers (acceleration sensors, pickups, or transducers) are available in a wide variety of sizes, shapes, performance characteristics, and prices. The five basic transducer types are servo force balance。 crystaltype or piezoelectric。 piezoresistive or silicon strain gauge type。 integral electronics piezoelectric。 and variable capacitance. Despite the different electromechanical transduction mechanisms, all use a variation of the spring mass system, and are classified as seismic transducers. Seismic Accelerometer Principle. All seismic accelerometers use some variation of a seismic or proof mass suspended by a spring structure in a case (see Figure 3). When the case is accelerated, the proof mass is also accelerated by the force transmitted through the spring structure. Then the displacement of the spring, the displacement of the mass within the case, or the forcetransmitted by the spring is transduced into an electrical signal proportional to acceleration. Accelerometers. Transducers designed to measure vibratory acceleration are called accelerometers. There are many varieties including strain gauge, servo force balance, piezoresistive (silicon strain gauge), piezoelectric (crystaltype), variable capacitance, and integral electronic piezoelectric. Each basic type has many variations and trade names. Most manufacturers provide excellent applications engineering assistance to help the user choose the best type for the application, but because most of these sources sell only one or two types, they tend to bias their assistance accordingly. For most applications, my personal bias is toward piezoelectric accelerometers with internal electronics. The primary limitation of these devices is temperature range. Although they exhibit lowfrequency rolloff, they are available with extremely lowfrequency capabilities. They provide a preamplified lowimpedance output, simple cabling, and simple signal conditioning, and generally have the lowest overall system cost. Most important to the user are the performance and environmental specifications and the price. What39。 s inside the box is irrelevant if the instrument meets the requirements of the application, but when adding to existing instrumentation it is important to be sure that the accelerometer is patible with the signal conditioning. Each type of accelerometer requires a different type of signal conditioning. Accelerometer Types. The most mon seismic transducers for shock and vibration measurements are:  Piezoelectric (PE)。 highimpedance output  Integral electronics piezoelectric (IEPE)。 lowimpedance output 8  Piezoresistive (PR)。 silicon strain gauge sensor  Variable capacitance (VC)。 lowlevel, lowfrequency  Servo force balance Piezoelectric (PE) sensors use the piez。