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1、-Development of Sensor New TechnologySensor is one kind ponent which can transform the physical quantity, chemistry quantity and the biomass into electrical signal. The output signal has the different forms like the voltage, the electric current, the frequency, the pulse and so on, which can satisfy
2、 the signal transmission, processing, recording, and demonstration and control demands. So it is the automatic detection system and in the automatic control industry .If automatic Technology is used wider, then sensor is more important.Several key words of the sensor：1Sensor ElementsAlthough there a
3、re e*ception ,most sensor consist of a sensing element and a conversion or control element. For e*ample, 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 displacem
4、ent. 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 sensor. Similar bination can be made for other energy input such as the
5、rmal. Photo, magnetic and chemical,giving thermoelectric, photoelectric,electromaanetic, and electrochemical sensor respectively.2Sensor SensitivityThe relationship between the measured and the sensor output signal is usually obtained by calibration tests and is referred to as the sensor sensitivity
6、 K1= output-signal increment / measured increment . In practice, the sensor sensitivity is usually known, and, by measuring the output signal, the input quantity is determined from input= output-signal increment / K1.3 Characteristics of an Ideal SensorThe high sensor should e*hibit the following ch
7、aracteristics.(a)high fidelity-the sensor output waveform shape be a faithful reproduction of the measured; there should be minimum distortion.(b)There should be minimum interference with the quantity being measured; the presence of the sensor should not alter the measured in any way.(c)Size. The se
8、nsor must be capable of being placed e*actly where it is needed.(d)There should be a linear relationship between the measured and the sensor signal.(e)The sensor should have minimum sensitivity to e*ternal effects, pressure sensor,for e*ample,are often subjected to e*ternal effects such vibration an
9、d temperature.(f)The natural frequency of the sensor should be well separated from the frequency and harmonics of the measurand.Sensors can be divided into the following categories：1 Electrical SensorElectrical sensor e*hibit many of the ideal characteristics. In addition they offer high sensitivity
10、 as well as promoting the possible of remote indication or mesdurement.Electrical sensor can be divided into two distinct groups:(a)variable-control-parameter types,which include:(i)resistance(ii)capacitance(iii)inductance(iv)mutual-inductance typesThese sensor all rely on e*ternal e*citation voltag
11、e for their operation.(b)self-generating types,which include(i)electromagnetic(ii)thermoelectric(iii)photoemissive(iv)piezo-electric typesThese all themselves produce an output voltage in response to the measurand input and their effects are reversible. For e*ample, a piezo-electric sensor normally
12、produces an output voltage in response to the deformation of a crystalline material; however, if an alternating voltage is applied across the material, the sensor e*hibits the reversible effect by deforming or vibrating at the frequency of the alternating voltage.2 Resistance SensorResistance sensor
13、 may be divided into two groups, as follows:(i)Those which e*perience a large resistance change, measured by using potential-divider methods. Potentiometers are in this group.(ii)Those which e*perience a small resistance change, measured by bridge-circuit methods. E*amples of this group include stra
14、in gauges and resistance thermometers.3 Capacitive SensorThe capacitance can thus made to vary by changing either the relative permittivity, the effective area, or the distance separating the plates. The characteristic curves indicate that variations of area and relative permittivity give a linear r
15、elationship only over a small range of spacings. Thus the sensitivity is high for small values of d.Unlike the potentionmeter, the variable-distance capacitive sensor has an infinite resolution making it most suitable for measuring small increments of displacement or quantities which may be changed
16、to produce a displacement.4 Inductive SensorThe inductance can thus be made to vary by changing the reluctance of the inductive circuit.Measuring techniques used with capacitive and inductive sensor:(a)A.C. e*cited bridges using differential capacitors inductors.(b)A.C. potentiometer circuits for dynamic measurements.(c)D.C. circuits to give a voltage proportional to velocity for a capacitor.(d)Frequency-mo
