自动化专业外文文献

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 satisfy 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 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 displacement. 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 input 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 sensor 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 exhibit 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 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 effects 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 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 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 example, 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