Basic knowledge of transducers
A transducer is a device which converts the quantity being measured into an optical, mechanical, or-more commonly-electrical signal. The energy-conversion 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. Ot知识竞赛主持词
her classification examples are pressure bellows, force diaphragm, pressure flapper-nozzle, and so on.
1、Transducer Elements
Although there are exception ,most transducers consist of a nsing element and a conversion or control element. For example, diaphragms,bellows,strain tubes and rings, bourdon tubes, and cantilevers are nsing elements which respond to changes in pressure or force and convert the physical quantities into a displacement. This displacem
ent may then be ud to change an electrical parameter such as voltage, resistance, capacitance, or inductance. Such combination of mechanical and electrical elements form electromechanical transducing devices or transducers. Similar combination can be made for other energy input such as thermal. Photo, magnetic and chemical,giving thermoelectric, photoelectric,electromaanetic, and electrochemical transducers respectively.
2、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 nsitivity K1= output-signal increment / measured increment . In practice, the transducer nsitivity 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 Transducer
The high transducer should exhibit the following characteristic塞内加尔世界杯
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a) high fidelity-the transducer 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 prence of the transducer sho77天
uld not alter the measured in any way.
c) Size. The transducer must be capable of being placed exactly where it is needed.
d) There should be a linear relationship between the measured and the transducer signal.
e) The transducer should have minimum nsitivity to external effects, pressure transducers,for example,are often subjected to external effects such vibration and temperature.
f) The natural frequency of the transducer should be well parated from the frequency and harmonics of the measurand.
4、Electrical Transducers
Electrical transducers exhibit many of the ideal characteristics. In addition they offer high nsitivity as well as promoting the possible of remote indication or mesdurement.
Electrical transducers can be div收据怎么写样本
ided into two distinct groups:
a) variable-control-parameter types,which include:
i)resistance
ii) capacitance
iii) inductance
iv) mutual-inductance types
The transducers all rely on external excitation voltage for their operation.
b) lf-generating types,which include
i) electromagnetic
ii)thermoelectric
iii)photoemissive
iv)piezo-electric types
The all themlves produce an output voltage in respon to the measurand input and their effects are reversible. For example, a piezo-electric transducer normally produces an output voltage in respon to the deformation of a crystalline material; however, if an alternating voltage is applied across the material, the transducer exhibits the reversible effect by deforming or vibrating at the frequency of the alternating voltage.
5、Resistance Transducers
Resistance transducers may be divided into two groups, as follows:
i) Tho which experience a large resistance change, measured by using potential-divider methods. Potentiometers are in this group.
ii)Tho which experience a small resistance change, measured by bridge-circuit methods. Examples of this group include strain gauges and resistance thermometers.
5.1 Potentiometers
A linear wire-wound potentiometer consists of a number of turns resistance wire wound around a non-conducting former, together with a wiping contact which travels over the barwires. The construction principles are shown in figure which indicate that the wiper displacement can be rotary, translational, or a combination of both to give a helical-type motion. The excitation voltage may be or d.c. and the output voltage is proportional to the input motion, provided the measuring device has a resistance which is much greater than the potentiometer resistance.
Such potentiometers suffer from the linked problem of resolution and electrical noi. Resolution is defined as the smallest detectable change in input and is dependent on the cross-ctional area of the windings and the area of the sliding contact. The output voltage is thus a rials of steps as the contact moves from one wire to next.
