One, capacitance sensor brief introduction

 

Capacitance sensor, english name is Capacitive Type Transducer, the commutation that is a kind of will other amount reflects the instrument that come out with the change of capacitance. Its are main by fluctuation two electrode, dielectric, underlay is formed, below pressure action, film produces certain deformation, the distance between fluctuation class produces change, bring about capacitance to change, but capacitance is not followed extremely span leaves change and linear change, its still need to measure circuit to undertake to outputting capacitance certain nonlinear compensation.

 

 

2, capacitance sensor classification

 

Capacitance type sensor is formed by two parallel electrode commonly, in its medium serves as with air between two electrode, below the premise that takes no account of edge effect, its capacitance can express to be C=εS/d, among them, ε represents the medium between two electrode (namely air) dielectric constant, s represents the area that covers each other between two electrode, d shows the distance between two electrode, capacitance suffers effect of these 3 parameter, the change of one parameter meets random make capacitance is able to change. Accordingly, can divide capacitance sensor the qualitative change that it is interpose to change model (the change of ε because the change of this C) , area change (the change of S because the change of this C) change with polar distance model (the change of D accordingly of C change.

 

 

3, capacitance sensor principle

 

Capacitance sensor also calls capacitance thing plan, its capacitance detecting element is based on principle of cylinder form capacitor to have the job, the coaxial and columnar plate that cylinder form capacitor basically is isolated from each other by two is formed, between two plate fill medium, criterion the capacity of this capacitor is C=2∏eL/lnD/d namely, among them, ε expresses the dielectric constant of the medium between two plate, l expresses two plate between the length of mutual coincide, d expresses outside cylindrical the diameter of plate, d expresses inside cylindrical the diameter of plate, when because be below fixed circumstance,undertaking metrical, its D, D, e3 parameter won’t change, can be informed its fluid according to measured capacitance accordingly height.

 

 

4, capacitance sensor actors or actress defect

 

Capacitance type sensor has definite advantage resistor type sensor, inductance type sensor relatively, but its also are not apple-pie, its also exist faultily, we are opposite below the actor defect of capacitance type sensor undertakes conformity:

 

Advantage: Low-cost, substantial; Sensitivity tall, accuracy is good; The structure is simple; Below harsh environment also applicably; Temperature stability is good; Have average effect; It is good that trends answers a gender; Overload capability is strong.

 

Defect: Output is nonlinear; The sensitivity of parasitism capacitance, distributinging capacitance, measure accuracy accessible, not stable; Connector is more complex.