毕业设计外文翻译---传感器的基础知识(编辑修改稿)

毕业设计外文翻译---传感器的基础知识(编辑修改稿)内容摘要：

issipation P of the fine wires of the potentiometer winding and is given by V=(PRt)1/2 . Resistance Strain Gauges Resistance strain gauges are transducers which exhibit a change in electrical resistance in response to mechanical strain. They may be of the bonded or unbonded variety . a) bonded strain gauges Using an adhesive, these gauges are bonded, or cemented, directly on to the surface of the body or structure which is being examined. Examples of bonded gauges are i) fine wire gauges cemented to paper backing ii) photoetched grids of conducting foil on an epoxyresin backing iii) a single semiconductor filament mounted on an epoxyresin backing with copper or nickel leads. Resistance gauges can be made up as single elements to measuring strain in one direction only, or a bination of elements such as rosettes will permit simultaneous measurements in more than one direction. 4 4 b) unbonded strain gauges A typical unbondedstraingauge arrangement shows fine resistance wires stretched around supports in such a way that the deflection of the cantilever spring system changes the tension in the wires and thus alters the resistance of wire. Such an arrangement may be found in mercially available force, load, or pressure transducers. Resistance Temperature Transducers The materials for these can be divided into two main groups: a) metals such as platinum, copper, tungsten, and nickel which exhibit and increase in resistance as the temperature rises。 they have a positive temperature coefficient of resistance. b) semiconductors, such as thermistors which use oxides of manganese, cobalt, chromium, or nickel. These exhibit large nonlinear resistance changes with temperature variation and normally have a negative temperature coefficient of resistance. a) metal resistance temperature transducers These depend, for many practical purpose and within a narrow temperature range, upon the relationship R1=R0*[1+a*(b1b2)] where a coefficient of resistance in ℃ 1,and R0 resistance in ohms at the reference temperature b0=0℃ at the reference temperature range ℃ . The international practical temperature scale is based on the platinum resistance thermometer, which covers the temperature range ℃ to ℃ . b) thermistor resistance temperature transducers Thermistors are temperaturesensitive resistors which exhibit large nonliner resistance changes with temperature variation. In general, they have a negative temperature coefficient. For small temperature increments the variation in resistance is reasonably linear。 but, if large temperature changes are experienced, special linearizing techniques are used in the measuring circuits to produce a linear relationship of resistance against temperature. Thermistors are normally made in the form of semiconductor discs enclosed in glass vitreous enamel. Since they can be made as small as 1mm,quite rapid response times are possible. Photoconductive Cells The photoconductive cell , uses a lightsensitive semiconductor material. The resistance between the metal electrodes decrease as the intensity of the light striking the semiconductor inc。