中英文翻译传感器共14页Word下载.docx

1、transducer for measuring displacement is classified as aresistance displacementtransducer. Other classification examples are pressure bellows, force diaphragm, pressureflapper-nozzle, and so on.1. Transducer ElementsAlthough there are exception ,most transducers consist of a sensing element and acon

2、versionor control element. For example, diaphragms,bellows,strain tubes and rings,bourdon tubes,and cantilevers are sensing elements which respond to changes in pressureor force and convert these physical quantities into a displacement. This displacement maythen be used tochange an electrical parame

3、ter such as voltage, resistance, capacitance, orinductance. Such combination of mechanical and electrical elements formelectromechanical transducing devices or transducers. Similar combination can be madefor other energy input such as thermal. Photo, magnetic and chemical,givingthermoelectric, photo

4、electric,electromaanetic,and electrochemical respectively.2. Transducer SensitivityThe relationship between the measured and the transducer output signal is usuallyobtained bycalibration tests and is referred to as the transducer sensitivity Kl=output-signal increment /measured increment. In practic

5、e, the transducer sensitivity is usuallyknown, and, bymeasuring the output signal, the input quantity is determined from input =output-signal increment / Kl.3. Characteristics of an Ideal TransducerThe high transducer should exhibit the following characteristics.a high fidelity-the transducer output

6、 waveform shape be a faithfulreproduction of the measured; there should be minimum distortion. b There shouldbe minimum interference with the quantity being measured; the presence of thetransducer should not alter the measured in any way.c Size. The transducer must be capable of being placed exactly

7、 where it is needed.d There should be a linear relationship between the measured and the transducersignal.e The transducer should have minimum sensitivity to external effects, pressuretransducers,for example,are often subjected to external effects such vibration andtemperaturefThe natural frequency

8、of the transducer should be well separated from thefrequency and harmonics of the measurand.4. Electrical TransducersElectrical transducers exhibit many of the ideal characteristics. In addition they offerhigh sensitivity as well as promoting the possible of remote indication ormesdurement.Electrica

9、l transducers can be divided into two distinct groups:a variable-control-parameter types,which include:i resistanceii capacitanceiii inductanceiv mutual-inductance typesThese transducers all rely on external excitation voltage for their operation.b self-generating types,which includei electromagneti

10、cii photoemissiveiv piezo-electric typesThese all themselves produce an output voltage in response to the measurand inputand their effects are reversible. For example, a piezo-electric transducer normallyproduces an output voltage in response to the deformation of a crystalline material;however, if

11、an alternating voltage is applied across the material, the transducer exhibitsthereversible effect by deforming or vibrating at the frequency of the alternatingvoltage.5. Resistance TransducersResistance transducers may be divided into two groups, as follows: i Those whichexperience a large resistan

12、ce change, measured by using potential-divider methods.Potentiometers are in this group.ii Those which experience a small resistance change, measured by bridge-circuitmethods. Examples of this group include strain gauges and resistance thermometers.5.1 PotentiometersA linear wire-wound potentiometer

13、 consists of a number of turns resistance wirewound around a non-conducting former, together with a wiping contact which travelsover the barwires. The construction principles are shown in figure which indicate that thewiper displacement can be rotary, translational, or a combination of both to give

14、ahelical-type motion. The excitation voltage may be either a.c. or d.c. and the outputvoltage isproportional to the input motion, provided the measuring device has a resistancewhich is much greater than the potentiometer resistance. Such potentiometers suffer fromthe linked problem of resolution and electrical noise.Resolution is defined as the smallest detectable change in input and is dependent onthe cross-sectional area of the windings and the area of the sliding contact. The outputvoltage is thus a serials of steps as the