Optical Tachometer Research Articles

Active Vibration Isolation of a Diesel Generator in a Small Marine Vessel: An Experimental Study

An active vibration isolation system is retrofitted to a diesel generator set in a tugboat to determine the effectiveness of such a system in a realistic practical environment. The system consists of six bespoke inertial actuators chosen to make minimal modifications to the machinery arrangement, and a DSP-based controller. Six accelerometers are collocated with the actuators on the top of six isolators to act as error sensors, and six accelerometers are placed below the isolators to give a measure of the global vibration of the ships structure below the generator set. A hydrophone is also placed in the water to give an indication of the underwater noise due to the generator. The control strategy employed is six-input and six-output decentralized adaptive feedforward control with the reference signal being derived from the signal from an optical tachometer on shaft between the engine and the generator. To suppress the vibration at all the dominant forcing frequencies, an electrical circuit generated the half engine orders required from the measured reference signal. The experimental results show that the combination of the active control system and the passive isolators is effective in reducing the global vibration and the acoustic pressure at the hydrophone position.

Motor Current Signature Analysis for Speed Estimation

The induction motors are widely applied due to their low price and ruggedness. There are several methods for speed estimation in the literature. The optical tachometer is an expensive and less reliable method for the speed measurement. Hence sensor less method for speed estimation is an important topic of research. In this paper, speed estimation of induction motor using motor current signature analysis is done. The comparative study of different methods shows that the motor current signature analysis (MCSA) is more accurate in speed estimation. This technique is experimentally verified on a 5HP, 3.7kW, 1430rpm 415V, 50Hz, 7.5A, 3Ø squirrel cage induction motor using LabVIEW. The experimental and simulation results show that the overall speed estimation error is within 5 rpm.

Investigation on high rotational speed calibration device

This paper presents the novel implementation of a high rotational speed device for optical tachometer calibration based on brushless DC coreless micro motor and FPGA technology at National Institute of Metrology (NIM), China. The structure of the device and key technology involved were described. The dual closed-loop control solution was explained. For control algorithm, virtual instrument technology is used to build up FPGA hardware from National Instrument and calibration software developed by Lab VIEW. Some calibration results of a laser tachometer are shown in the measurement range from 40000 to 99999 r/min. The expanded calibration uncertainty is 1 × 10−4, k = 2. This high rotational speed calibration device is the first successful technical realization of the measurement unit of r/min (RPM) with resolution of 1 r/min for engineering applications in China and, therefore, used as an important working standard at NIM for the feasible traceability of high-precision optical tachometers national wide at high measurement range above 40000 r/min.

Development and Assessment of Planetary Gear Unit for Experimental Prototype of Vertical Axis Wind Turbine

Abstract The theoretical calculation for development of planetary gear unit of wind turbine (WT) and its experimental tests are presented in the paper. Development of experimental prototypes from composite materials is essential to determine capability of element and its impact on feature. Two experimental scale prototypes of planetary gear unit for WT were developed for such purposes. Hall transducer, servomechanisms and optical tachometers were used to obtain results, comparison analysis of theoretical and actual data was performed as well as quality assessment of experimental prototypes of planetary gear unit. After kinematic and load analysis as well as control of rotation frequency, it is possible to declare that the unit is able to operate at designated quality. Theoretical calculations and test results obtained are used for industrial WT prototype development.

Measurement of Air Flow Rate Sensitivity to the Differential Pressure Across a Server Rack in a Data Center

Presently, air cooling is the most common method of thermal management in data centers. In a data center, multiple servers are housed in a rack, and the racks are arranged in rows to allow cold air entry from the front (cold aisle) and hot air exit from the back (hot aisle), in what is referred as hot-aisle-cold-aisle (HACA) arrangement. If the racks are kept in an open room space, the differential pressure between the front and back of the rack is zero. However, this may not be true for some scenarios, such as, in the case of cold aisle containment, where the cold aisle is physically separated from the hot data center room space to minimize cold and hot air mixing. For an under-provisioned case (total supplied tile air flow rate < total rack air flow rate) the pressure in the cold aisle (front of the rack) will be lower than the data center room space (back of the rack). For this case, the rack air flow rate will be lower than the case without the containment. In this paper, we will present a methodology to measure the rack air flow rate sensitivity to differential pressure across the rack. Here, we use perforated covers at the back of the racks, which results in higher back pressure (and lower rack air flow rate) and the corresponding sensitivity of rack air flow rate to the differential pressure is obtained. The influence of variation and nonuniformity in the server fan speed is investigated, and it is observed that with consideration of fan laws, one can obtain results for different average fan speeds with reasonable accuracy. The measured sensitivity can be used to determine the rack air flow rate with variation in the cold aisle pressure, which can then be used as a boundary condition in computational fluid dynamics (CFD)/rapid models for data center air flow modeling. The measured sensitivity can also be used to determine the change in rack air flow rate with the use of different types of front/back perforated doors at the rack. Here, the rack air flow rate is measured using an array of thermal anemometers, pressure is measured using a micromanometer, and the fan speed is measured using an optical tachometer.

Design, Implementation and Performance Analysis of a Low-cost Optical Tachometer

Electrical and mechanical machineries are used in industrial and domestic applications. Measurement of speed of revolving machineries is necessary for their proper functioning and controlling. Tachometer is an instrument which is used to measure the speed of revolving shaft, gear and pulley. This paper describes the basic construction of a low cost optical tachometer and analyzes its performance. The basic tachometer circuit consists of two stages. In the first stage monostable wired around IC NE555 is used, and in the second stage a digital counter based 4-digit counter IC 74C926 is used for the construction of the tachometer. A 5V regulated power supply circuit and an infrared light source circuit are also used. The instrument can measure speed upto 9999 RPM. This speed measurement instrument performs well in terms of accuracy, and can be very useful due to its simplicity and low cost. DOI: http://dx.doi.org/10.3329/iiucs.v7i0.12263 IIUC Studies Vol.7 2011: 107-116

Eddy current braking experiment using brake disc from aluminium series of A16061 and A17075

The electromagnetic braking using eddy current was studied, focused on two series of aluminium as the brake disc which are A16061 and A17075. This paper presents the comparison for both series in a few varied parameters related to eddy current braking such as air-gap, number of turns and brake disc thickness. Optical tachometer has been used along with PULSE analyzer to capture the speed (rpm) and time (s). The findings shows that the smaller the air-gap, the larger of electromagnet turns and the thicker disc thickness is, will generate higher braking torque to stop the rotational motion of disc brake and give great performance for eddy current braking. Thos parameters that been evaluated also addressed a potential on expanding this knowledge to develop an electromagnetic braking system to replace the conventional braking system.

Non-contact strip speed measurement using electrostatic sensing and correlation signal-processing techniques

Accurate and reliable strip speed measurement is desirable in many manufacturing industries for both monitoring and control purposes. This paper presents the recent development in non-contact measurement of strip speed using electrostatic sensors in combination with correlation signal-processing techniques. A pair of metal electrodes is used to obtain signals from the moving strip. The speed of the strip is then determined from the known fixed spacing between the electrodes and the time delay between the two signals. Experimental tests were conducted on a motorized strip speed test rig under a range of conditions. An optical tachometer was used as a reference instrument to gauge the accuracy of the strip speed measurement system. The system design considerations, advantages and limitations are addressed. Results demonstrate that the system is capable of measuring strip speed robustly with a relative error not greater than ±1.8% and a repeatability of 2.5% over the speed range of 0.8 to 10 m s−1.

Plow Power Requirements for Forestry Site Preparation

In this field study, data were collected to determine power requirements required by a trailing site preparation plow and the magnitudes of dynamic forces experienced by a plow during normal operation and during impact with stumps or other obstructions. Drawbar pull data were collected from five different tillage treatments on a recently harvested loblolly pine (Pinus taeda) site in central Alabama. The five treatments were: 1) a coulter, ripping shank, and four bedding disks; 2) a coulter, ripping shank, and two bedding disks; 3) a coulter and ripping shank; 4) a coulter alone; and 5) a ripping shank alone. A 330 kN [75 000 lb] capacity tension load cell was used to measure the drawbar load, a GPS receiver recorded tractor speed, four direct current displacement transducers (DCDT’s) monitored the depth of the disks, and two optical tachometers measured the speed of the tractor’s front and rear drive shafts. Each treatment produced significantly different drawbar loads (to alpha levels less than 0.001). The resulting mean loads were 46.0 kN [10 300 lb], 33.5 kN [7530 lb], 31.5 kN [7080 lb], 15.8 kN [3560 lb], and 43.4 kN [9760 lb] for treatments one through five, respectively. Maximum recorded drawbar load during a collision with a stump was 338.9 kN [76 188 lb].

A hybrid active/passive exhaust noise control system for locomotives

A prototype hybrid system consisting of active and passive components for controlling far-field locomotive exhaust noise has been designed, assembled, and tested on a locomotive. The system consisted of a resistive passive silencer for controlling high-frequency broadband noise and a feedforward multiple-input, multiple-output active control system for suppressing low-frequency tonal noise. The active system used ten roof-mounted bandpass speaker enclosures with 2-12-in. speakers per enclosure as actuators, eight roof-mounted electret microphones as residual sensors, and an optical tachometer that sensed locomotive engine speed as a reference sensor. The system was installed on a passenger locomotive and tested in an operating rail yard. Details of the system are described and the near-field and far-field noise reductions are compared against the design goal.

An optical tachometer for short‐path measurement of flow speeds in shallow overland flows: improved alternative to dye timing

AbstractTracers, such as fluorescein dye, are widely employed to measure overland flow speeds by time‐of‐travel along measured flow paths. Among several disadvantages of this method are the involvement of human reaction time when using stop‐watches, and the relatively long travel path that is consequently needed for reliable timing. Long flow paths mean that local variability along the flow path cannot be detected.This paper describes a new optical tachometer that overcomes these limitations, as well as offering other advantages. It is based on the use of a small floating reflector target that is carried on the surface tension film, and which passes between two reflective sensors mounted above the flow. The new device allows virtual ‘spot’ measurements of surface flow speed over a path as short as 1 cm, and eliminates the influence of human reaction time. The new device is battery powered and portable, and provides an improved alternative to dye timing in many field and laboratory applications. Its use will allow the collection of more refined data than have hitherto been easily achievable. Copyright © 2003 John Wiley & Sons, Ltd.

Water‐soluble polymers. LXXXII. Shear degradation effects on drag reduction behavior of dilute polymer solutions

AbstractDrag reduction measurements were conducted on extensively characterized poly(ethylene oxide) and poly(acrylamide) utilizing a fully automated rotating disk rheometer equipped with an optical tachometer, torque transducer, and software allowing real‐time data acquisition. The instrument sensitivity allowed the study of concentrations as low as 0.1 ppm. In addition, previously immeasurable concentration‐ and time‐dependent shear degradation effects were readily observed. A power law equation was shown to adequately correlate the percentage of drag reduction and the volume fraction for each polymer. Furthermore, an empirical shift factor was utilized to superimpose data from all the systems that were studied. By conducting measurements in the proper concentration and time domains, it was possible to extract the minimal concentration for the maximum drag reduction efficiency in the absence of shear degradation. The resulting values were significantly higher than those previously reported by our laboratories for poly(ethylene oxide) and poly(acrylamide). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1211–1221, 2001

Fourier analysis of wing beat signals: assessing the effects of genetic alterations of flight muscle structure in Diptera

A method for determining and analyzing the wing beat frequency in Diptera is presented. This method uses an optical tachometer to measure Diptera wing movement during flight. The resulting signal from the optical measurement is analyzed using a Fast Fourier Transform (FFT) technique, and the dominant frequency peak in the Fourier spectrum is selected as the wing beat frequency. Also described is a method for determining quantitatively the degree of variability of the wing beat frequency about the dominant frequency. This method is based on determination of a quantity called the Hindex, which is derived using data from the FFT analysis. Calculation of the H index allows computer-based selection of the most suitable segment of recorded data for determination of the representative wing beat frequency. Experimental data suggest that the H index can also prove useful in examining wing beat frequency variability in Diptera whose flight muscle structure has been genetically altered. Examples from Drosophila indirect flight muscle studies as well as examples of artificial data are presented to illustrate the method. This method fulfills a need for a standardized method for determining wing beat frequencies and examining wing beat frequency variability in insects whose flight muscles have been altered by protein engineering methods.

Description and performance testing of a low friction, twin-propeller anemometer with wind vane

A twin air-bearing anemometer with wind vane has been developed for measuring vertical and horizontal wind speed. The configuration of the propellers and the use of air bearings and optical tachometers are the primary innovations leading to better sensitivity and dynamic response. The anemometer response is linear for a wind speed as low as 0.08 m s-1 and initiation of propeller rotation occurs at approximately 0.06 m s-1. The dynamic response of the anemometer with optical tachometer is approximately 20% faster than for commercially available propeller anemometers with tachogenerators. The wind vane orients the propellers into the wind at wind speeds greater than 0.2 m s-1 and its distance response ranged from 0.25 to 0.45 m. This wind sensor provides a low cost and reliable mechanical sensor for flux density measurements.

Analog Signal Processing for Tachometer, Accelerometer, and Torque-Speed Curve Plotting of Motors by Use of Silicon Solar Cells

An optical tachometer is developed by the analog processing of the signals obtained from the silicon solar cell displacement sensors. Differentiating the speed signal, satisfactorily smooth acceleration signal is obtained by simple filtering. The torque-speed curve plotting for small motors by the application of this technique and the effects of the filtering on the plot are described.

An Optical Tachometer for Measurement of the Wing-Beat Frequency of Free-Flying Insects

ABSTRACT The wing-beat frequency of flying insects has generally been measured by acoustic methods, but even with modern condenser microphones and frequency-selective amplification the signal available from smaller insects may be inadequate. A microphone had to be placed within 1 cm of the midge Smittia aterrima (Mg.) to produce a satisfactory signal and no signals could be obtained from Thrips sp. (Thysanoptera). Acoustic recordings of flying insects in the laboratory may also be degraded by the excited resonant frequencies of the cage material. The optical tachometer uses the minute changes in the intensity of ambient light reflected from an insect’s beating wings to produce an amplified electrical output at the wing-beat frequency, producing an adequate signal from a very much greater range than would be obtained by acoustic methods. With this device Smittia aterrima could be measured at a distance of 1 m, Drosophila melanogaster Mg, at 1·2 m, and larger insects from a much greater range: Calliphora vicina (R-D.) 7 m, and Bombus sp. 10 m. No difficulty is found when making measurements through the sides of transparent flight cages. The sensitivity of the device seems sufficient for recording Thrips, although this has not yet been tested.

Optical tachometry for monitoring nuclear magnetic resonance sample spinning rates

A simple optical tachometer utilizing fibre optics and solid state electronics has been designed and constructed in order to monitor sample turbine spin speeds on a Varian HA 100D nuclear magnetic resonance spectrometer. By use of a bifurcated fibre optical path, light is transmitted to the turbine strobe, modulated, and returned to the detector within the same plastic-sheated glass fibre bundle. Rotational information can thus be retrieved without disturbing the magnetic field or sample environment. The relation of sample spinning speed to spectral quality is discussed.