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【正文】 such vibration and temperature. f) The natural frequency of the transducer should be well separated from the frequency and harmonics of the measurand. Electrical Transducers Electrical transducers exhibit many of the ideal characteristics. In addition they offer high sensitivity as well as promoting the possible of remote indication or mesdurement. Electrical transducers can be divided into two distinct groups: a) variablecontrolparameter types,which include: i) resistance ii) capacitance iii) inductance iv) mutualinductance types These transducers all rely on external excitation voltage for their operation. b) selfgenerating types,which include i) electromagic ii) thermoelectric iii) photoemissive iv) piezoelectric types These all themselves produce an output voltage in response to the measurand input and their effects are reversible. For example, a piezoelectric transducer normally produces an output voltage in response to the deformation of a crystalline material。 1 1 Basic knowledge of transducers A transducer is a device which converts the quantity being measured into an optical, mechanical, ormore monlyelectrical signal. The energyconversion process that takes place is referred to as transduction. Transducers are classified according to the transduction principle involved and the form of the measured. Thus a resistance transducer for measuring displacement is classified as a resistance displacement transducer. Other classification examples are pressure bellows, force diaphragm, pressure flappernozzle, and so on. Transducer Elements Although there are exception ,most transducers consist of a sensing element and a conversion or control element. For example, diaphragms,bellows,strain tubes and rings, bourdon tubes, and cantilevers are sensing elements which respond to changes in pressure or force and convert these physical quantities into a displacement. This displacement may then be used to change an electrical parameter such as voltage, resistance, capacitance, or inductance. Such bination of mechanical and electrical elements form electromechanical transducing devices or transducers. Similar bination can be made for other energy input such as thermal. Photo, magic and chemical,giving thermoelectric, photoelectric,electromaaic, and electrochemical transducers respectively. Transducer Sensitivity The relationship between the measured and the transducer output signal is usually obtained by calibration tests and is referred to as the transducer sensitivity K1= outputsignal increment / measured increment . In practice, the transducer sensitivity is usually known, and, by measuring the output signal, the input quantity is determined from input= outputsignal increment / K1. Characteristics of an Ideal Transducer The high transducer should exhibit the following characteristics a) high fidelitythe transducer output waveform shape be a faithful reproduction of the measured。 there should be minimum distortion. b) There should be minimum interference with the q
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