永豐商業銀行股份有限公司.ppt

Transducer,Device when activated from one form energy converted to another quantity or Device which converts one physical quantity or condition to another,Physical quantity heat , intensity of light, flow rate, liquid level, humidity etc Sensor : sense physical quantity,Classification of transducers,Based on principle of transduction Active & passive Analog & digital Inverse transducer,Based on principle used,Thermo electric Magneto resistive Electro kinetic Optical,Passive transducer,Device which derive power reqd. for transduction from auxiliary power source - externally powered Eg : resistive, inductive, capacitive Without power they will not work,Active transducer,No extra power reqd. to produce I/p Self generating Draw power from input applied Eg. Piezo electric xtal used for accelartion measurement,Analog transducer,convert I/p quantity into an analog o/p Analog o/p- a continuous fn. Of time Eg. Strain gauge, L VDT, thermocouple,Digital transducer,Converts I/p into an electrical o/p in the form of pulses,Inverse transducer,Which converts electrical signal to physical quantity,Transducer for pressure measurement,What is pressure? force/ unit area Unit (N/sq.m) Pa Pressure measured can be absolute , gauge or differential depending on type of reference,Types of pressure transducers,Gravitational eg : manometer Elastic force converted to strain eg. Diaphragm, capsule, bellows, bourdon tubes,Diaphragm,Common pressure sensing elastic element Thin circular plate stretched & fastened at its periphery Made of elastic alloys of bronze,phosphor bronze, stainless steel or alloys like Monel, Nickel span -C,Structure flat or corrugated,Top view of flat type,Top view of corrugated type,Flat type high natural frequency Corrugated for large deflections,Capsule,Capsule,Two corrugated metal diaphragms sealed together at periphery Forms a shell like structure One diaphragm has a port at centre to admit pressure to be measured Other diaphragm linked to a moveable mechanical part.,Capsule,Displacement proportional to difference b/w outer & inner pressure.,Bourdon tubes,curved or twisted metallic tubes with elliptical cross section Sealed at one end Tends to straighten when pressure applied. Angular sensitivity proportional to pressure applied,Spirial bourdon tubes,Bourdon tubes C type,Helical type,Tube in the form of helix,Bourdon tube,More sensitive to shock & vibrations Good repeatability,Bellows,Bellows,Thin walled cylindrical sheets with deep convolutions sealed at one end Sealed end moves axially when pressure is applied No. of convolution s vary from- 2 to 50 depends on range, operating temp Used for low pressure measurement,Bellows,displacement y = 2.n. A q P Rx 2 /( Et 2 .) where n no. of convolutions A q- effective area Et - youngs modulus of elasticity Rx radius of diaphragm P pressure ie, Y P,Resistive type,Eg. Strain gauge,Capacitive,Inductive type,Eg. LVDT,Measurement of velocity,Velocity linear or angular,Linear velocity,Electromagnetic transducers O/p voltage E = /t = N I/ R2 . dR/dt where N I/ R2 is a constant R- reluctance so E proportional to reluctance R proportional to air gap & air gap proportional to velocity,Types Moving coil Moving magnetic,Angular velocity,Tachometer - types Mechanical Electrical MHD sensor magneto hydrodynamic sensor highly sensitive High precision,Transducer for vibration,Vibrations give early warning of impending conditions which may develop &vlead to complete failure & destruction of equipment Used in power plants, turbines,Most vibrations are sinusodial in nature Got amp & freq. Amp gives displacement By measuring dis