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1、Progress in Materials ScienceVolume 46, Issues 34, 2001, Pages 461504The selection of sensorsJ Shieh, J.E Huber, N.A Fleck, , M.F AshbyDepartment of Engineering, Cambridge University, Trumpington Street, Cambridge CB2 1PZ, UKAvailable online 14 March 2001.http:/dx.doi.org/10.1016/S0079-6425(00)00011
2、-6, How to Cite or Link Using DOIPermissions & ReprintsAbstractA systematic method is developed to select the most appropriate sensor for a particular application. A wide range of candidate sensors exist, and many are based on coupled electrical and mechanical phenomena, such as the piezoelectric, m
3、agnetostrictive and the pyro-electric effects. Performance charts for sensors are constructed from suppliers data for commercially available devices. The selection of an appropriate sensor is based on matching the operating characteristics of sensors to the requirements of an application. The final
4、selection is aided by additional considerations such as cost, and impedance matching. Case studies illustrate the selection procedure.KeywordsSensors; Selection; Sensing range; Sensing resolution; Sensing frequency1. IntroductionThe Oxford English Dictionary defines a sensor as “a device which detec
5、ts or measures some condition or property, and records, indicates, or otherwise responds to the information received”. Thus, sensors have the function of converting a stimulus into a measured signal. The stimulus can be mechanical, thermal, electromagnetic, acoustic, or chemical in origin (and so on
6、), while the measured signal is typically electrical in nature, although pneumatic, hydraulic and optical signals may be employed. Sensors are an essential component in the operation of engineering devices, and are based upon a very wide range of underlying physical principles of operation.Given the
7、 large number of sensors on the market, the selection of a suitable sensor for a new application is a daunting task for the Design Engineer: the purpose of this article is to provide a straightforward selection procedure. The study extends that of Huber et al. 1 for the complementary problem of actu
8、ator selection. It will become apparent that a much wider choice of sensor than actuator is available: the underlying reason appears to be that power-matching is required for an efficient actuator, whereas for sensors the achievable high stability and gain of modern-day electronics obviates a need t
9、o convert efficiently the power of a stimulus into the power of an electrical signal. The classes of sensor studied here are detailed in the Appendices.2. Sensor performance chartsIn this section, sensor performance data are presented in the form of 2D charts with performance indices of the sensor a
10、s axes. The data are based on sensing systems which are currently available on the market. Therefore, the limits shown on each chart are practical limits for readily available systems, rather than theoretical performance limits for each technology. Issues such as cost, practicality (such as impedanc
11、e matching) and reliability also need to be considered when making a final selection from a list of candidate sensors.Before displaying the charts we need to introduce some definitions of sensor characteristics; these are summarised in Table1.1 Most of these characteristics are quoted in manufacture
12、rs data sheets. However, information on the reliability and robustness of a sensor are rarely given in a quantitative manner.Table 1. Summary of the main sensor characteristicsRangemaximum minus minimum value of the measured stimulusResolutionsmallest measurable increment in measured stimulusSensing
13、 frequencymaximum frequency of the stimulus which can be detectedAccuracyerror of measurement, in% full scale deflectionSizeleading dimension or mass of sensorOpt environmentoperating temperature and environmental conditionsReliabilityservice life in hours or number of cycles of operationDriftlong t
14、erm stability (deviation of measurement over a time period)Costpurchase cost of the sensor ($ in year 2000)Full-size tableIn the following, we shall present selection charts using a sub-set of sensor characteristics: range, resolution and frequency limits. Further, we shall limit our attention to se
15、nsors which can detect displacement, acceleration, force, and temperature.2 Each performance chart maps the domain of existence of practical sensors. By adding to the chart the required characteristics for a particular application, a subset of potential sensors can be identified. The optimal sensor
16、is obtained by making use of several charts and by considering additional tabular information such as cost. The utility of the approach is demonstrated in Section 3, by a series of case studies.2.1. Displacement sensorsConsider first the performance charts for displacement sensors, with axes of reso
17、lution versus range R, and sensing frequency f versus range R, as shown in Fig. 1andFig. 2, respectively.Fig. 1.Resolution versus sensing range for displacement sensors.View thumbnail imagesFig. 2.Sensing frequency versus sensing range for displacement sensors.View thumbnail images2.1.1. Resolution
18、sensing range chart (Fig.1)The performance regime of resolution versus range R for each class of sensor is marked by a closed domain with boundaries given by heavy lines (see Fig.1). The upper limit of operation is met when the coarsest achievable resolution equals the operating range =R. Sensors of
19、 largest sensing range lie towards the right of the figure, while sensors of finest resolution lie towards the bottom. It is striking that the range of displacement sensor spans 13 orders of magnitude in both range and resolution, with a large number of competing technologies available. On these log
20、arithmic axes, lines of slope +1 link classes of sensors with the same number of distinct measurable positions, . Sensors close to the single position line =R are suitable as simple proximity (on/off) switches, or where few discrete positions are required. Proximity sensors are marked by a single th
21、ick band in Fig.1: more detailed information on the sensing range and maximum switching frequency of proximity switches are summarised in Table2. Sensors located towards the lower right of Fig.1 allow for continuous displacement measurement, with high information content. Displacement sensors other
22、than the proximity switches are able to provide a continuous output response that is proportional to the targets position within the sensing range. Fig.1 shows that the majority of sensors have a resolving power of 103106 positions; this corresponds to approximately 1020 bits for sensors with a digi
23、tal output.Table 2. Specification of proximity switchesProximity switch typeMaximum switching distance (m)Maximum switching frequency (Hz)Inductive6104110155000Capacitive110361021200Magnetic31038.51024005000Pneumatic cylinder sensors (magnetic)Piston diameter 81033.21013005000Ultrasonic1.21015.2150P
24、hotoelectric31033002020,000Full-size tableIt is clear from Fig.1 that the sensing range of displacement sensors cluster in the region 105101 m. To the left of this cluster, the displacement sensors of AFM and STM, which operate on the principles of atomic forces and current tunnelling, have z-axis-s
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