Applications for velocity measurement include: Controlling the speed at which metal stock is fed into a machine tool.

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2 Applications Applications for velocity measurement include: Controlling the speed at which metal stock is fed into a machine tool. Measuring the approach speed of a robotic tool onto its target. Monitoring the speed of a generator in an electric power station. An airport radar system measuring the speed of an approaching aircraft using the Doppler effect. Measuring an automobile s wheel speed in order to provide feedback to an antilock brake system.

3 Classification Linear Velocity Measurement Reference Based Measurement Seismic Devices Utilizing Differentiation of Displacement Linear Velocity Transducer (LVT) Conversion of Linear to Rotational Velocity Doppler Shift Light Interference Methods VISAR System Velocity Measurement Angular Velocity Measurement Absolute Velocity Relative Velocity Tachometers Counter Types Stroboscopy Gyroscopes Tachogenerator Photoelectric Tachometer Strain Gauge Tachometer Switch Tachometer Rotating Magnetic Sensor Optical Sensor Hall Effect Sensor Wiegand Sensor

4 Introduction Linear Velocity definition : Time rate of change of position of the object. Direction : direction of change in position Type: Vector quantity Magnitude : Speed Common units : m / s ; miles / h Angular Velocity definition : Time rate of change of angular position of the object. Direction : direction of the axis about which the object is turning Type : Vector quantity Magnitude : Rotational speed Common units : RPM (revolution per minute)

5 Measurement of Linear Velocity A precise theory y 2 v 1 v 2 average speed = y t 2 2 y t 1 1 = y t y 1 v y t y = t lim = 0 dy dt t 1 t 2 v y ( t) = vi + a y ( t) t ti dt Methods - Reference Based methods - Seismic devices

6 Reference Based Methods Definition : Measurements made in which the instrumentation has components on both the moving object and the reference frame for the measurement. Methods include measuring through: Differentiation of displacement LVT Conversion of Linear to angular velocity Doppler effect sensors Light interference methods VISAR system

7 Utilizing differentiation of displacement Method : Using some type of position transducer to record the position-time function of the moving object and then differentiate this function to get speed-time function. Example : Two pickups spaced a known distance apart; recording the time for the object edge to pass between the pickups. Result : average speed Application : Determining the muzzle speed of a projectile. Notes : Selection of an acceptable transducer; Range, Resolution and mass loading are important parameters. Because differentiation is a noise generating process, particular care must be exercised to minimize the noise of displacement.

8 Linear Velocity Transducer Basis : Linear Generator Theory : When a coil cuts the magnetic field lines around a magnet, a voltage is induced in it. Displacement range : 0.5 to 24 inches mv ips Typical sensitivity range : 40 to 600 e i BLV e i = induced voltage in the coil B = magnetic field strength L = length of wire in the coil V = speed of the coil relative to the Manufacturers : Trans-Tek Robinson Halpern Macro Sensors GE Co. magnet

9 Conversion of Linear to Rotational Velocity Method : Placing a rack on the moving object and having the rack drive a pinion gear Example : same principle is used in automobile s speedometer

10 Doppler Effect Sensors Theory : Doppler Shift Method : Transmitting a wave to moving object and receiving it back. 2 f D = V Cosθ λ Applications : Weather broadcast Automatic emergency break of car. (VORAD) Manufacturers : Canon Baron Services

11 Light Interference Methods Theory:classical Michelson Interferometer Method : a beam of monochromatic light is split into two beams; one is directed onto a stationary mirror, the other onto the target. The super position of reflected beams is directed to the lens, pin hole and then counter. Advantages : High accuracy Constraints : Target should have a highly polished surface and very little tilt during the test. Manufacturer : Polytech Device name : Laser Doppler Velocimeter

12 VISAR System Basis : Interferometry Range of work : 100 m to 10 s km s Sensitivity : 100 to 400 fringes per m s Advantages : -Highly accurate -working with specularly or diffusely reflecting surfaces -insensitive to target s tilting Applications : Weapon technology Mining technology Space technology Geophysical & planetary researches Manufacturer : Valyn International Controlled fusion energy researches

13 Seismic Devices Structure : a mass attached to the transducer base by a spring. The base is attached to the surface whose motion is desired. Approach : 1) A displacement transducer as the secondary transducer. 2) a velocity transducer as the secondary transducer. Applications : Earthquake studying Oil well logging and related works Manufacturers :Wilcoxon Research Inc Teledyne Brown Corp. Nanometrics Inc.

14 Measurement of Angular velocity Classification : Relative : measurements are taken with respect to the base of the item being Angular Velocity measured. Absolute : Reference of the measurement is the earth Idea : Generating a pulse train or sine wave whose frequency is proportional to angular velocity. Devices : Tachometers Counter Type Sensors Stroboscopes

15 Tachometers 1) Tachogenerator Basis : A rotating generator produces a voltage signal proportional to the rotational velocity of the input shaft. DC generator : produces a voltage level proportional to speed. AC generator : produces an ac output voltage with a frequency proportional to speed. Manufacturers : Manufacturers : GE Co. ; Kollmorgen motion Technologies ; Micro Mo Electronics ; Tamagava Sieki ; Hubner ; Magnetic SPA.

16 Tachometers 2) Photoelectric Tachometer Structure : A disk with reflecting markings attached to the shaft. A light source and a light detector. Output : a train of pulses whose frequency is proportional to shaft s RPM.

17 Tachometers 3) Strain Gauge Tachometer Structure : A thin rod with a bonded strain gauge attached. The end of the rod has a small wheel that rests on the dist attached to the shaft. Output : A sinusoidal waveform whose frequency is proportional to the RPM.

18 Tachometers 4) Switch Tachometer Structure : a rod and an offset disk attached to the shaft. Output : a train of pulses whose frequency is proportional to Rotational velocity.

19 Counter Type Sensors 1) Rotating Magnet Sensor Structure : A magnetic pickup and a rotating slotted disk of a ferromagnetic material. Advantage : No need of external power source Manufacturers : Smith Systems Optec Technology Balluf Daytronic Corp. Celduc Inc. Honeywell

20 Counter Type Sensors 2) Optical Sensor Structure : A light emitter and a light detector Note : The effect of external light sources Manufacturers : Banner Eng. Corp. Sharp Aromat Corp. Leuze electronic Co. Dinel Co.

21 Counter Type Sensors 3) Hall Effect Sensor IB V H = ne d Theory : Hall Effect Application : Wheel speed sensor for anti lock braking system Manufacturers : Optec Technology Inc. Allegro Micro Cherry Corp.

22 Counter Type Sensors 4) Wiegand Effect Sensor Theory : Wiegand Effect Structure : Wiegand wire ; an alternative magnetic field ; a coil Manufacturer : HID Corp.

23 Stroboscope description : A source of flash light with adjustable frequency Manufacturers : BBE Corp. Extech Instruments Corp. Monarch Instrument Co. Shimpo Instrument Co.

24 Conditioning Circuits For a Sensor whose output level is important For a sensor whose out put is a train of pulses or similar outputs.

25 Iran s s Market Available sensors in Market : Tachometer : Model DT2235A ; produced by Shenzhen Sampo Instrument Co.Ltd. ; for Tomant ; imported and sold by Landa Electronic. Hall Effect Sensor : Models UGN3503 for 1000 Tomans and UGN3113 for 500 Tomans ; produced by Allegro Micro ; imported and sold by Jahan Kit Co. Optical Sensor : Models 1s58 ; produced by sharp ; for 500 Tomans and SG23FF produced by Kodenshi of Korea ; the price is 500 Tomans and the importer and seller is Jahan Kit Co. Companies working in this field : Jahan Kit Persian Electronic Paya Electronic

26 Conclusion The problem of velocity measurement is somewhat different from that of measurement of other quantities in that there is not a large number of transducer types and transducer manufacturers from which to choose for a given problem. Frequently, the problem is such that the person must use his/her knowledge of measurement of other quantities and ingenuity to develop a velocity measurement method suitable for the problem at hand. Velocity is often obtained by differentiation of displacement or integration of acceleration. The most common idea for Velocity measurement is to generate a signal whose frequency is proportional to the velocity. Making use of the effects of a magnetic field is another idea. The other idea is to utilize the frequency shift or phase shift of waves caused by motion.

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