INSTRUMENTATION & SENSORS (3ET4)

1. INSTRUMENTATION & SENSORS(3ET4) LECTURE 1: INTRODUCTION Kamlesh T. Kahar Faculty of Elect. & Telecommunication Engineering SSGMCE

2. Definition • Instrumentation • It is the branch of engineering that deals with measurement & control of process variables within a production/manufacturing area. • Measurement • A method to obtain information regarding the physical values of the variable.

3. Terminologies • Physical quantity: variable such as pressure, temperature, mass, length, etc. • Data: Information obtained from the instrumentation/measurement system as a result of the measurements made of the physical quantities • Information: Data that has a calibrated numeric relationship to the physical quantity. • Parameter: Physical quantity within defined (numeric) limits.

4. Purpose of a measurement system measurand Sensor, signal conditioning, display Man, tracking control etc

5. Terminology • Measurand: Physical quantity being measured. • Calibration: Implies that there is a numeric relationship throughout the whole instrumentation system and that it is directly related to an approved national or international standard. • Test instrumentation: It is a branch of instrumentation and most closely associated with the task of gathering data during various development phases encountered in engineering, e.g. flight test instrumentation for testing and approving aircraft.

6. Terminologies • Transducer: A device that converts one form of energy to another. • Electronic transducer: It has an input or output that is electrical in nature (e.g., voltage, current or resistance). • Sensor: Electronic transducer that converts physical quantity into an electrical signal. • Actuator: Electronic transducer that converts electrical energy into mechanical energy.

7. Why measurement? • In the case of process industries and industrial manufacturing… • To improve the quality of the product • To improve the efficiency of production • To maintain the proper operation.

8. Why instrumentation? • To acquire data or information (hence data acquisition) about parameters, in terms of: • putting the numerical values to the physical quantities • making measurements otherwise inaccessible. • producing data agreeable to analysis (mostly in electrical form) • Data Acquisition Software (DAS) – data is acquired by the instrumentation system.

9. Types of measurements • Direct comparison • Easy to do but… less accurate • e.g. to measure a steel bar • Indirect comparison • Calibrated system; consists of several devices to convert, process (amplification or filtering) and display the output • e.g. to measure force from strain gages located in a structure

10. Generalised measuring system • Stage 1: A detection-transducer or sensor-transducer, stage; e.g. Bourdon tube • Stage 2: A signal conditioning stage; e.g. gearing, filters, bridges • Stage 3: A terminating or readout-recording stage; e.g. printers, oscilloscope General Structure of Measuring System

11. Types of instruments in measurements • Passive Instruments • the quantity being measured simply modulates (adapts to) the magnitude of some external power source. • Active Instruments • the instrument output is entirely produced by the quantity being measured • Difference between active & passive instruments is the level of measurement resolution that can be obtained.

12. Active Instruments • e.g. Float-type petrol tank level indicator

13. Petrol tank level indicator • The change in petrol level moves a potentiometer arm, and the output signal consists of a proportion of the meter reading which varies according to the position of float.

14. Passive Instruments • e.g. Pressure-measuring device

15. Passive pressure gauge • The pressure of the fluid is translated into a movement of a pointer against scale. • The energy expanded in moving the pointer is derived entirely from the change in pressure measured: there are no other energy inputs to the system.

16. Analogue Instruments • An analogue instrument gives an output that varies continuously as the quantity being measured; e.g. Deflection-type of pressure gauge

17. Digital Instruments • A digital instrument has an output that varies in discrete steps and only have a finite number of values; e.g. Revolution counter

18. Application • Home • Thermometer • Barometer • Watch • Road vehicles • speedometer • fuel gauge • Industry • Automation • Process control • Boiler control

19. Syllabus Unit-I : Basics of Transducers • Transducer: Definition, Classification, Selection criteria. Errors, loading effects, Transducer Specifications, calibration, Generalized Instrumentation diagram. • Static characteristics: Accuracy, Precision, Sensitivity, Threshold, Resolution, Repeatability and Hysteresis. • Errors: Gross error, Systematic error, Random error, Limiting error. • Statistical Parameters: Arithmetic mean Average deviation Standard deviation. Probable error, Histogram, Normal & Gaussian curve of errors.

20. Syllabus Unit-II: Measurement of Displacement, Liquid Level • Measurement of Displacement: Resistive, Capacitive, Inductive • Measurement of Liquid Level: Resistive, Capacitive, Inductive, Ultrasonic, Gamma Rays.

21. Syllabus Unit-III: Measurement of Temperature Measurement of Temperature: Resistance temperature detector (RTD):Principle, types, Configurations, construction and working of RTD, Material for RTD, advantages, disadvantages and applications of RTD. Thermistors: Principle, types (NTC and PTC), characteristics, Construction and working of Thermistor, Materials, specifications of Thermistor, applications. Thermocouples: Principle, thermoelectric effect, See beck effect, Peltier effect, laws of thermocouple, cold junction Compensation method, thermopile, thermocouple emf measurement method. Pyrometers: Principle, Construction and working of Radiation and optical pyrometers and its Applications, LM 335.

22. Syllabus Unit-IV: Measurement of Pressure, Flow, Humidity. • Measurement of Pressure: Primary pressure sensors - elastic elements like bourdon tube, diaphragm, and bellows. Electrical/Secondary Pressure • Transducers: Capacitive, piezo-electric and its material, variable reluctance, LVDT. • Differential pressure measurement: Capacitive. Low Pressure (Vacuum): Pirani gauge, thermocouple gauge, hot cathode ionization gauge. • Flow Measurement: ultrasonic, electromagnetic & hotwire Anemometer. • Flow Measurement: ultrasonic, electromagnetic & hotwire Anemometer.

23. Syllabus Unit-V: Measurement of Velocity, Strain & Miscellaneous Sensors Velocity Measurement: Using photo detectors (both linear & angular velocity), Stroboscope. Strain Measurement: Introduction, types of strain gauge, gauge factor calculation, materials for strain gauge, resistance strain gauge bridges, temperature compensation and applications of strain gauges. Miscellaneous Sensors: Noise (sound) Sensors Characteristics of sound, levels of sound pressure, sound power and sound intensity. Smart sensors: Objective, block diagram, advantages and disadvantages.

24. Syllabus Unit-VI: Data acquisition and applications of Electronic Instruments • Analog & Digital data acquisition system.: Generalized block diagram of data acquisition system(DAS), objective of DAS, signal conditioning of inputs, single channel DAS, Multichannel DAS, computer based DAS • Digital transducer: optical encoders, shaft encoders • pH and blood pressure measurement.

25. Books Recommended