Industrial instrumentation


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Industrial instrumentation

  1. 1. Shot Term Training Programme on Industrial Instrumentation11/26/12 1
  2. 2. SyllabusBasic concept of measurement, Transducers and theirclassification, Measurement of non-electrical quantitieslike Angular and Linear Displacement, Strain,Vibration, Pressure, Liquid flow, Temperature, Forceand Torque. Instrumentation amplifiers, Dataacquisition and conversion, Digital signal transmissionand processing, Microprocessor based instrumentation.Input and output devices and Displays. 11/26/12 2
  3. 3. INTRODUCTIONAn instrumentation system is an assembly ofvarious instruments and componentsinterconnected to measure analyse andcontrol the electrical, thermal hydraulic andother non-electrical physical quantities.11/26/12 3
  4. 4. Elements of Measurement System The whole operation can be described interms of three functional elements. Eachfunctional element is made up of a distinctcomponent or group of components, whichperforms required and definite steps inmeasurement. These may be taken as basicelements, whose scope is determined by theirfunctioning rather than their construction.11/26/12 4
  5. 5. Elements of Measurement System Primary sensing element Variable conversion element Data-presentation element Terminating stage Signal Conditioning Transmitting element11/26/12 5
  6. 6. Primary sensing element The quantity under measurement makes itsfirst contact with primary sensing element ofa measurement system. Immediately after thisa transducer converts measured into ananalogous electrical signal. This is true inmost of the cases but in many cases themeasured quantity is directly converted intoan electrical quantity by a transducer.11/26/12 6
  7. 7. Variable conversion element The output of the primary sensing element maybe any kind of electrical signal. It may be a voltage, afrequency or some other electrical parameter. Often thisoutput does not suit to the system. For the instrument toperform the desired function, it may be necessary toconvert this output to some other suitable form whileretaining the original signal. The function of variablemanipulation element is to manipulate the signal . 11/26/12 7
  8. 8. Data-presentation element The information about the quantity undermeasurement has to be conveyed to thepersonnel handling the instrument or thesystem for monitoring control, or analysispurposes. The information conveyed must bein a form intelligible to the personnel.11/26/12 8
  9. 9. Data-presentation element cont.. These devices may be analogue or digital indicating instruments like Ammeters Recorders like magnetic tapes, High speed camera Storage type CRT Printers Analogue and digital computers.11/26/12 9
  10. 10. Terminating stage The final stage in a measurement system isknown as terminating stage. When a control device is used for the finalmeasurement stage it is necessary to applysome feedback to the input signal toaccomplish the control objectives. 11/26/12 10
  11. 11. Signal Conditioning Many a times one has to perform certain operationson the signal before it is transmitted further. Theseprocesses may be linear like amplification, alternation,integration, differentiation addition and subtraction.Some non-linear processes like modulation, detection,sampling filtering, chopping and clipping etc. areperformed on the signal to bring to the desired form.This is called signal conditioning.In fact the element that follows the primary sensingelement in any instrument or instrumentation systemshould be called signal-conditioning element. 11/26/12 11
  12. 12. Transmitting elementWhen the elements of an instrument arephysically separated, it becomes necessary totransmit data from one to another.The element that performs this function iscalled a transmitting element.11/26/12 12
  13. 13. Typical Instrumentation SystemConsists of following operation.Monitoring processes: - An instrumentationsystem has an essential function of monitoringthe process. It simply indicates the value orcondition of parameter under the study in theprocess.11/26/12 13
  14. 14. Process ControlIn order to control the process variables liketemperature, pressure, humidity etc. these quantitiesmust be measured at the desired location in theprocessing plant. They are compared with the referenceor desired signal and the error signal is amplified tooperate the actuator in controlling the process. Thecorrective action goes on till the controlled output issame as the desired output, in that case the error signalwill be zero and the actuator will not operate. 11/26/12 14
  15. 15. TRANSDUCERS A device, which converts one form of energyinto another form of energy, is called transducer.For the field of electrical instrumentationtransducer is defined as a device, which convertsa physical quantity (or a physical condition) intoan electrical signal Transducer is often referredas pick-up. 11/26/12 15
  16. 16. Type of Transducers Primary Transducers Secondary Transducers11/26/12 16
  17. 17. Primary transducersPrimary transducers are detectors, which sensea physical phenomenon. The example of primary transducer is athermocouple, which senses the radiant energyand directly converts it into an analogouselectrical output, which is a voltage.11/26/12 17
  18. 18. Secondary transducers Secondary transducers convert the analogousoutput into on electrical signal.11/26/12 18
  19. 19. Classification of transducersThe transducers can be active, that is selfgenerating type or passive, that is externallypowered.Passive transducers derive the power requiredfor energy conversion from an external powersource. Potentiometers are the examples ofpassive transducers.11/26/12 19
  20. 20. Active transducers(i) Thermoelectric,(ii) Piezoelectric,(iii) Photovoltaic(iv) Magnatostrictive,(v) Electro kinetic(vi) Electrodynamic,(vii) Electromagnetic,(viii) Pyroelectric,(ix) Galvanic11/26/12 20
  21. 21. Passive transducers(i) Resistive (viii) Hall effect(ii) Inductive (ix) Synchro(iii) Capacitive (x) Gyro(iv) Photoconductive (xi) Radio active(v) Magneto resistive absorption(vi) Thermo resistive (xii) Ionic conduction(vii) Elastoresistive11/26/12 21
  22. 22. Basic requirements of Transducers 1. Ruggedness 2. Linearity 3. Repeatability 4. Convenient instrumentation 5. High stability & reliability 6. Good dynamic response 7. Excellent mechanical characteristics 8. Built-in integrated device with noise and other defects minimized11/26/12 22
  23. 23. Types of Detectors Electrical Transducers Pressure Transducers Piezzo-electric Transducers Oscillation transducers Inductive Transducer11/26/12 23
  24. 24. Advantages of Electrical transducerover mechanical transducers1. Minimized friction2. Minimized mass-inertia effect3. Easy Electrical amplification4. Very small power electrical/electronic system controlled5. The electrical output can be easily used, transmitted and processed for the purpose of measurement.6. Miniaturization due to integrated circuits and use of microprocessors.7. Easy Data transmission etc.11/26/12 24
  26. 26. Major electrical transducers fordisplacement measurement  Variable resistance- Potentiometric/strain gauge  Variable inductance-LVDT/ variable reluctance  Variable capacitance  Synchros and resolvers11/26/12 26
  27. 27. Advantages of Synchros and resolversi. Infinite resolutionii. No wear of rotation, except at slip ringsiii. System operating at much higher speediv. Relatively insensitive characteristics tostray cable capacitancesv. High reliability and accuracyvi. Useful operating angle of 360 degree andcapable of continuous rotations. 11/26/12 27
  28. 28. MEASUREMENT OF STRAIN11/26/12 28
  29. 29. Types of strain gauges Mechanical gauges Optical gauges Electrical strain gauges11/26/12 29
  30. 30. Types of electrical strain gauges  Wire gauges i. Flat grid type ii. Wrap around type iii. Single wire gauge iv. Woven type  Unbonded Strain gauges  Foil gauges  Semiconductor strain gauges  Thin film gauges11/26/12 30
  31. 31. MEASUREMENT OF PRESSURE11/26/12 31
  32. 32. Classification of transducers 1. Gravitational i.e. Manometer 2. Elastic type Diaphragms Capsule Bourdon tube Bellows11/26/12 32
  33. 33. Transduction methods: 1. Potentiometric Device 2. Strain Gauge transducer 3. Variable reluctance Sensor 4. LVDT type transducer 5. Variable capacitance Device 6. Thin Film Pressure transducer 7. Force Balance transducer 8. Piezoelectric Pressure Transducer11/26/12 33
  34. 34. MEASUREMENT OF FLOW11/26/12 34
  35. 35. Classification of Flow meters 1. Head type flow meter based on differential pressure measurement i.e.Orifice plate, Ventury tube, Flow nozzle and Pitot tube 2. Electromagnetic flow meter 3. Rotameter (Variable area meter) 4. Mechanical flow meter 5. Anemometer 6. Ultrasonic flow meter 7. Vortex flow meter11/26/12 35
  37. 37. Types of Temperature sensors 1. Mechanical temperature sensors i. Liquid in glass thermometer ii. Liquid filled systems iii. Vapour pressure thermometer 2. Resistance type temperature sensors 3. Platinum resistance thermometer 4. Thermocouples 5. Thermisters 6. Solid state sensors 7. Quartz thermometer 8. Radiation thermometer 9. Optical pyrometer11/26/12 37
  39. 39. Types of transducers 1. Force Measuring sensor – Load cell: i. Column type device ii. Proving rings iii. Cantilever beam iv. Shear type load cell v. Pressducer 2. Digital force transducer 3. Force balance device 4. Hydraulic load cell 5. Electronic weighing system11/26/12 39
  40. 40. Torque measuring transducers 1. Absorption type 2. Transmission type 3. Stress type 4. Deflection type11/26/12 40
  42. 42. Important features i. Selectable gain with high gain accuracy and gain linearity ii. Differential input capability with high common mode rejection, even with sources having unbalance high out put impedances iii. High stability of gain with low temperature coefficient iv. Low DC offset and drift errors referred to input v. Low out put impedance11/26/12 42