Research On Precise Pneumatic-Electric Displacement Sensor With Large Measurement Range

Pneumatic measurement technique is a kind of non-contact measurement technique.Pneumatic measuring instrument has several advantages including simple construction,high accuracy,easy to use,good economy,high reliability,and good self-cleaning ability.Thus,it is applied widely to modern industry such as automobile,home appliance,weaponry and so on.Pneumatic measurement uses compressed air as its medium,and it transforms the variation of physical dimension of measured object to the change of gas pressure and quantity of flow.After that,measurement data would be given by drake device or dial instrument.Traditional pneumatic measurement technique has two disadvantages: 1.The nonlinearity of the principle of measurement,the accuracy cannot be compromised with measuring range.For example,when the measuring range is 50?m,accuracy is 1?m.However,when the measuring range is 250?m,accuracy can only reach 10?m.2.It cannot operate with automation equipment collaboratively.Pneumatic-electric measurement technique is developed from traditional pneumatic measurement technique,and it can overcome the shortcoming of traditional pneumatic measurement technique.The aim of the research is to achieve the high accuracy and wide range as well,so that gas measurement technique could be widely applied.Beyond that,it can complete on-line automatic measuring system combining with computer technique.Pneumatic-electric displacement sensor is the core of pneumatic-electric measurement technique with high accuracy and wide range as well.It requires good linearity with displacement and electric signal.This report begins with theoretical analysis of pneumatic-electric measurement technique.It analyzes the status and character of gas flow at first.Then it analyzes the operating characteristic of classical backpressure gas circuit.On this basis,it puts forward three sections transfer approach of pneumatic-electric displacement sensor.In the first section,differential pressure gas circuit system is applied.It can decrease passive error of gas pressure and increase the measuring accuracy at the same time.Thus,it can complete the transform from displacement signal to air pressure signal.In the second section,differential pressure sensor is used,and it transfers the variation of differential pressure to the variation of voltage signal.Finally,it can complete the transform from differential air pressure signal to voltage signal.The device composed of the gas circuit of the first section and the electric circuit of the second section is a pneumatic-electric transducer.The character of this kind of pneumatic-electric transducer is nonlinearity.Aiming to decrease this kind of nonlinearity,a section of corrector needs to be added to realize linearization and measuring range extension.Corrector is a nonlinearity correction arithmetic and it can be realized by software or hardware.In consideration of the interchangeability of pneumatic-electric transducer,hardware corrector is used in this project.On the basis of the theoretical analysis mentioned above,a precise pneumatic-electric displacement sensor system with large measurement range is developed composed of differential motion pneumatic system,differential pressure electronic transition system,and nonlinear electronic corrective system.This experiment precisely tests the input and output signals of this pneumatic-electric displacement sensor before and after nonlinearity correction.It also applies multilevel fold subsection linearization circuit to achieve the range enlargement and the index of measurement range of 180?m with accuracy of 1?m.At the same time,high repeatability and stability can be achieved so that it also has high practical value.