1、Development of Sensor New Technology Sensor is one kind component 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 sati
2、sfy 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： 1 Sensor Elements Although
3、there are exception ,most sensor 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 di
4、splacement. This displacement may then be used to change an electrical parameter such as voltage, resistance, capacitance, or inductance. Such combination of mechanical and electrical elements form electromechanical transducing devices or sensor. Similar combination can be made for other energy inpu
5、t such as thermal. Photo, magnetic and chemical,giving thermoelectric, photoelectric,electromaanetic, and electrochemical sensor respectively. 2 Sensor Sensitivity The relationship between the measured and the sensor output signal is usually obtained by calibration tests and is referred to as the se
6、nsor sensitivity 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 Sensor The high sensor should exhibi
7、t the following characteristics. (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
8、 way. (c)Size. The sensor must be capable of being placed exactly 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 external effects, pressure sensor,for example,are often subjected to external ef
9、fects such vibration and 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 Sensor Electrical sensor exhibit many of the ideal characteristics. In addition
10、they offer high sensitivity 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 types These sensor all
11、rely on external excitation voltage for their operation. (b)self-generating types,which include (i)electromagnetic (ii)thermoelectric (iii)photoemissive (iv)piezo-electric types These all themselves produce an output voltage in response to the measurand input and their effects are reversible. For ex
12、ample, a piezo-electric sensor normally 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 exhibits the reversible effect by deforming or vibrating at the frequency of the alternating volt
13、age. 2 Resistance Sensor Resistance sensor may be divided into two groups, as follows: (i)Those which experience a large resistance change, measured by using potential-divider methods. Potentiometers are in this group. (ii)Those which experience a small resistance change, measured by bridge-circuit
14、methods. Examples of this group include strain gauges and resistance thermometers. 3 Capacitive Sensor The 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
15、area and relative permittivity give a linear relationship 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 d
16、isplacement or quantities which may be changed to produce a displacement. 4 Inductive Sensor The 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. excited bridges using differential capacit
17、ors 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-modulation methods, where the change of C or L varies the frequency of an oscillation circuit. Important features of capacitive and induct
18、ive sensor are as follows: (i)resolution infinite (ii)accuracy0.1% of full scale is quoted (iii)displacement ranges 25*10-6 m to 10-3m (iv)rise time less than 50us possible Typical measurands are displacement, pressure, vibration, sound, and liquid level. 5 Linear Variable-differential Ttransformer
19、6 Piezo-electric Sensor 7 Electromagnetic Sensor 8 Thermoelectric Sensor 9 Photoelectric Cells 10 Mechanical Sensor and Sensing Elements In information age, the information industry includes information gathering, transmission, process three parts, namely sensor technology, communication, computer technology. Because of ultra large scale integrated circuits rapid development after having been developed Modern computer technology and communication, not only requests sensor precision reliability, speed of
