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1、Chapter 7 Measurement of velocity, acceleration and vibration,School of mechanical and power engineering/Henan polytechnic university,Contents 7.1 Overview 7.2 Measurement of Velocity 7.3 Measurement of Acceleration 7.4 Vibration test,Chapter Seven Measurement of velocity, acceleration and vibration
2、,7.1 Overview,Measurement of velocity and acceleration for vehicle, train, ship, plane, etc，and that of their moving attitude Rotational velocity for output shaft speed of engine and generator Velocity of rolled plate, strip, bar, tubing material Measurement of vibration for large devices and engine
3、ering Applications in inertial navigation,7.1 Overview,Velocity：a vector which shows the direction and rate of motion. 物体直线运动时单位时间内的位移量，m/s Acceleration：a vector which shows the direction and magnitude of changes in velocity.物体运动时单位时间内的速度增量，m/s2 Rotational Velocity：物体运动时单位时间内的转数，r/min Angular Veloci
4、ty：物体单位时间内转过的角度，rad/s,Contents 7.1 Overview 7.2 Measurement of Velocity 7.3 Measurement of Acceleration 7.4 Vibration test,Chapter Seven Measurement of velocity, acceleration and vibration,7.2 Measurement of Velocity,From motion form： measurement of linear velocity(线速度) and angular velocity(角速度) Fro
5、m reference: measurement of absolute velocity(绝对速度) and relative velocity(相对速度) From numerical feature: measurement of average velocity(平均速度) and instantaneous velocity(瞬时速度)The average velocity of an object is the total displacement during some extended period of time, divided by that period of tim
6、e.,Average velocity method,光束切断法(短距离平均速度法),Average velocity method,Correlation velocity measurement,Average velocity method,Correlation velocity measurement Strong anti-interference ability and make the measurement under complex interference conditions . Application: measurement of plane, ship, and
7、rolling mill strip, etc. In principle, two sensors is set in the direction of velocity of a moving object, and the velocity can be measured using cross-correlation principle.,Average velocity method,Average velocity method,Spatial filter velocity measurement(空间滤波器测速法) 利用可选择一定空间频率的空间滤波器件与被测物体同步运动，然后在
8、单位空间内测得相应的时间频率f，求得运动体的运动速度。,Pitot Tube velocity measurement,Bernoullis equation of ideal incompressible fluid 理想不可压缩流体在重力场中作定常流动时，具有三种形式的能量：位势能、压力势能和动能，在流线上任何一处三者能量之和保持恒定。,Pitot Tube velocity measurement,Measuring principle,误差来源： 皮托管的方向与流体方向不对准； 皮托管直径不为零，静压孔实际静压力降低； 流体受皮托管的滞止，使滞止点上游的静压力增大。,Pitot Tub
9、e velocity measurement,全静压管 静压孔距前端不小于8倍管径，可减小头部激波对静压的影响； 静压孔上部4个，下部6个，两侧没有，可在大仰角飞行时减小静压误差； 装有加温装置，防止在高空飞行时结冰,Pitot Tube velocity measurement,飞机空速表 开口膜盒（指示空速） 真空膜盒（真空速）,当外界气温T实与该气层标准气温T标不等时，应按下式进行修正：,Pitot Tube velocity measurement,皮托管测速装置利用了流体速度和流体动压力之间的关系；在测量时直接测量的是压力，然后再计算出速度，属于间接测量；测量了运动物体和流体的相对速
10、度。 皮托管装置的结构坚固耐用，稳定可靠。,Doppler velocity measurement,Doppler effect,Doppler velocity measurement,Doppler velocity measurement,多普勒测速的优点：用光的波长作基准，精度高；光电探测器输出频率信号，抗干扰能力强。,Doppler velocity measurement,Backscattering Doppler velocity measurement,光源与光电探测器放置于运动物体的一侧，仪器设计时结构紧凑,Doppler velocity measurement,Bac
11、kscattering difference Doppler velocity measurement,Doppler velocity measurement,Difference Doppler velocity measurement,For the beam O1,For the beam O2,Frequency difference is not concerned with the position of photo-electric detector, and it measures in any direction. 可使用大口径的接收透镜，使粒子散射的光能量极大地被利用，提
12、高信噪比。,Doppler velocity measurement,Optical fibre Doppler velocity measurement of blood,探头体积小，便于调整测量位置，可以深入到难以测量的角落；抗干扰能力强，可在高电压、强电磁感应等环境中使用。密封型的光纤探头可直接放入液体中使用。,Doppler velocity measurement,Satellite tracking system 电磁波多普勒效应,Gyroscope angular velocity measurement,Structure of gyroscope 2-DOF gyro Sin
13、gle-DOF gyro,Gyroscope angular velocity measurement,Support mode of gyroscope 液浮陀螺仪 气动陀螺仪 静电陀螺仪 挠性陀螺仪,Gyroscope angular velocity measurement,Basic characteristics of gyroscope Gyroscopic inertia(定轴性)：当陀螺仪的转子高速旋转时，如果不受任何外加力矩的作用，其主轴将稳定地保持在惯性空间初始方向上，这种特性称为陀螺仪定轴性或者稳定性。 角动量H越大，摩擦力矩越小，则主轴方向越稳定。,Gyroscope
14、angular velocity measurement,Basic characteristics of gyroscope Gyro-precession(进动性)：当转子高速旋转时，如果外加力矩M作用在陀螺仪的某一框架旋转轴上，迫使主轴绕另一框架的轴旋转，主轴以最短的途径向外力矩的方向靠拢。 在实际使用中如果内框架和外框架重合，陀螺仪将会失去了一个自由度，这种情况被称为“环架自锁”。 陀螺的进动是没有惯性滞后,Gyroscope angular velocity measurement,微分陀螺仪角速度测量,Gyroscope angular velocity measurement,F
15、ibre-optic gyroscope Invented with Sagnac effect 光纤陀螺对角速度的敏感轴是单轴，常使用三个或四个光纤陀螺构成惯性测量组合,Velocity measurement using timing method,Rotation speed measurement,Measuring method Expressed by revolution per minute. That is r/min,By measuring principle: 模拟法 计数法 同步法,By transforming mode： 机械式 电气式 光电式 频闪式,Centr
16、ifugal tachometer,离心式转速表具有测量结果显示直观、成本低、运行可靠、坚固耐用等优点，故在生产、维修现场使用较多。但是离心式转速表的测量原理简单，测量精度相对较低。,Photoelectric tachomer,接触式,非接触式,Magnetoelectric tachometer,随着转速下降输出感应电动势的幅值也随之减小，当转速低到一定程度时，电压幅值将会无法检测出来。这种传感器不适合于低转速测量。,Stroboscopic tachometer,Stroboscopic effect(频闪效应) 物体在人的视野中消失后，人眼视网膜上能在一段时间内保持视觉印象，即视后暂留现象。其维持时间，在物体平均亮度条件下，约为(1/51/20)s的范围。 Measuring principle 用一个频率连续可调的闪光灯照射被测旋转轴上的某一固定标记(如齿轮的齿，圆盘的辐条或在旋转轴上涂以黑白点)，并调节闪光频率f，直到旋转轴上出现一个单定像为止，即达到n=f的条件，这时便可以从电子计数器或圆刻度盘上读出被测的转速值。,
