AVS ENGINEERING COLLEGE, SALEM-3
Unit-I – Introduction
Functional Elements of Measurement System
Three main functional elements :
1. Primary sensing element
2. Variable conversion element
3. Data presentation element
Block Diagram of Functional Elements of Measurement System
Static Characteristics:
1. Accuracy, 2. Precision, 3.Sensitivity, 4.Resolution, 5. Static error ,
6.Range , 7.Span,8.Reproducibility,9.Repeatability,10.Drift , 11.
Dead zone, 12.Threshold, 13.Significant figures,14.Linearity ,
15.True value
Dynamic characteristics:
1. Speed of response , 2.Measuring lag, 3.Fidelity, 4.Dynamic error
Errors in measurement:
1. Gross errors
2. Systematic errors
3. Random errors
Statistical Evaluation of Data Measurement:
1. Arithmetic mean
2. Median
3. Mode
4. Deviation from the mean
5. Average deviation
6. Standard deviation
7. Variance
Standards & Calibration
Unit-II – Electrical and Electronics Instruments
Classification of Instruments
Analog Instruments:
Graduated scale with a pointer.
Must be adjusted to zero before use.
Here the output is a continuous function of time and bears a constant
relationship with the input
Digital Instruments:
Provides a reading in numbers.
Easier to read.
Provides a more accurate reading
Controlling Force
Deflection force : Air Friction Damping
Fluid Friction Damping:
Eddy Current Damping:
Permanent Magnet Moving Coil Instrument ( PMMC )
Moving Iron Instruments - MI
Moving Iron Repulsion Type Instrument
Basic D.C.Ammeter
Basic shunt resistance is calculated as:
Rm = Internal resistance Ω
Rsh = Shunt resistance Ω
Im = Full scale deflection current
of basic meter in A
Ish = Shunt current in A
I = Current to be measured in A
Vsh = Voltage drop across shunt resistance in V
Vm = Voltage drop across basic meter is V
Shunt resistance and basic meter are in parallel
Vsh = Vm and IshRsh = ImRm
D.C. Basic Voltmeter with Multiplier
Values of multiplier required to extend voltage range:
Im = Full scale deflection current of basic
meter in A
Rm = Internal resistance of basic meter in Ω
Rs = Multiplier resistance in Ω
v = Voltage across the basic meter for the
current Im in V
V = Full range voltage of the instrument
v = ImRm
V = Im(Rm + Rs)
Multiplying factor ‘m’ = V/v = 1 + Rs /Rm
Classification of Digital Voltmeter
Block Diagram of Servo Potentiometric Type DVM
Block Diagram of Successive Approximation Type DVM
Linear RampType DVM
Voltage to Time Conversion Waveform
Staircase RampType DVM
Block Diagram of Digital Multimeter
Types of Single Phase Wattmeter
(i) Electrodynamometer Wattmeter
(ii) Low Power Factor Wattmeter
(iii) Three Wattmeter Method
Unit –III - Comparison Methods of Measurements
Potentiometers:
Laboratory Type D.C. Potentiometer
Duo – range (Two Range ) Potentiometer
Vernier Potentiometer
Deflection Type Potentiometer
Bridge Circuit
Maxwell Bridge
unknown inductance
Hay Bridge
unknown inductance
Schering Bridge
unknown capacitance
Anderson Bridge
Wien Bridge
Transformer Ratio Bridge
Measurement of Resistance
Measurement of Capacitance
Measurement of Phase Angle
Self Balancing Bridges
Sources of Electromagnetic Interference
1. AC power circuits, Solenoids switching fluorescent lighting, radio
frequency transmitters
2. Welding equipment
3. Inductive or capacitive coupling
4. Earths of slightly different potential
Earth Loops
Electrostatic Interference and Screening
Unit – IV - Storage and Display Devices
Component's of Magnetic Tape Recorder
1. Recording Head
2. Magnetic Tape
3. Reproducing Head
4. Tape Transport Mechanism
5. Conditioning Devices
Recording Head
Direct Recording
Cathode Ray Oscilloscopes
Cathode-Ray Tube
Digital Storage Oscilloscope
Unit –V - Transducers and Data Acquisition Systems
Resistive Transducers
Passive transducer: Device which derive power reqd. for transduction from
auxiliary power source - externally powered
Example: Resistive, Inductive, Capacitive
Active Transducer: No extra power reqd. to produce I/p. Self generating
Example: Piezo electric used for acceleration measurement
Analog Transducer: Convert I/p quantity into an analog o/p. Analog o/p- a
continuous function of time.
Example: Strain gauge, L VDT, thermocouple
Digital Transducer: Converts I/p into an electrical o/p in the form of pulses
Inverse Transducer: Converts electrical signal to physical quantity
Wire Strain Gauges
Thermistors
Inductive Transducer
Linear Variable Differential Transformer (LVDT)
Characteristics of lvdt
Capacitive Transducers
Piezo Electric Transducers
Optical Sensor - Transducer
Schematic Diagram of Fiber Optic Transducer
Data Acquisition System
Architecture of Smart Sensor
